Name

    ARB_shader_objects

Name Strings

    GL_ARB_shader_objects

Contributors

    Kurt Akeley
    Allen Akin
    Dave Baldwin
    Bob Beretta
    Pat Brown
    Matt Craighead
    Cass Everitt
    Mandar Godse
    Evan Hart
    Phil Huxley
    Deron Dann Johnson
    James Jones
    Dale Kirkland
    John Kessenich
    Steve Koren
    Jon Leech
    Bill Licea-Kane
    Barthold Lichtenbelt
    Kent Lin
    Benjamin Lipchak
    Rob Mace
    Michael McCool
    Teri Morrison
    Jeremy Morris
    Glenn Ortner
    Ian Romanick
    Randi Rost
    Jeremy Sandmel
    Folker Schamel
    Mik Wells

Contact

    Barthold Lichtenbelt, 3Dlabs, Inc. (barthold 'at' 3dlabs.com)
    Randi Rost, 3Dlabs, Inc. (rost 'at' 3dlabs.com)

Notice

    Copyright (c) 2003-2013 The Khronos Group Inc. Copyright terms at
        http://www.khronos.org/registry/speccopyright.html

Specification Update Policy

    Khronos-approved extension specifications are updated in response to
    issues and bugs prioritized by the Khronos OpenGL Working Group. For
    extensions which have been promoted to a core Specification, fixes will
    first appear in the latest version of that core Specification, and will
    eventually be backported to the extension document. This policy is
    described in more detail at
        https://www.khronos.org/registry/OpenGL/docs/update_policy.php

IP Status

    As described in the Contributor License, which can be found at
    http://www.3dlabs.com/support/developer/ogl2/specs/3dlabs_contributor.pdf.

Status

    Complete. Approved by the ARB on June 11, 2003.
    Updated revision 0.89 approved by the ARB on June 17, 2004.

Version

    Last Modified Date: December 14, 2009
    Author Revision: 0.90

Number

    ARB Extension #30

Dependencies

    OpenGL 1.0 is required.

    This extension is written against version 1.10 of the OpenGL Shading
    Language Specification.

    The extension is written against the OpenGL 1.4 Specification.

Overview

    This extension adds API calls that are necessary to manage shader
    objects and program objects as defined in the OpenGL 2.0 white papers by
    3Dlabs.

    The generation of an executable that runs on one of OpenGL's
    programmable units is modeled to that of developing a typical C/C++
    application. There are one or more source files, each of which are
    stored by OpenGL in a shader object. Each shader object (source file)
    needs to be compiled and attached to a program object. Once all shader
    objects are compiled successfully, the program object needs to be linked
    to produce an executable. This executable is part of the program object,
    and can now be loaded onto the programmable units to make it part of the
    current OpenGL state. Both the compile and link stages generate a text
    string that can be queried to get more information. This information
    could be, but is not limited to, compile errors, link errors,
    optimization hints, etc. Values for uniform variables, declared in a
    shader, can be set by the application and used to control a shader's
    behavior.

    This extension defines functions for creating shader objects and program
    objects, for compiling shader objects, for linking program objects, for
    attaching shader objects to program objects, and for using a program
    object as part of current state. Functions to load uniform values are
    also defined. Some house keeping functions, like deleting an object and
    querying object state, are also provided.

    Although this extension defines the API for creating shader objects, it
    does not define any specific types of shader objects. It is assumed that
    this extension will be implemented along with at least one such
    additional extension for creating a specific type of OpenGL 2.0 shader
    (e.g., the ARB_fragment_shader extension or the ARB_vertex_shader
    extension).

Issues

    1) What to do if part of a shader pair is not present?

    DISCUSSION: There are several shader types that go together. For
    example, a VERTEX_SHADER and a FRAGMENT_SHADER form a pair that is part
    of the geometry pipeline. It is not required to supply both shader types
    of a pair in a program object.

    RESOLUTION: If one or the other of a pair is not present in the program
    object, OpenGL will substitute the standard 1.4 OpenGL pipeline for the
    one not present. The most likely place for this substitution to happen
    is the link stage. Note that it is defined elsewhere exactly what part
    of the OpenGL 1.4 pipeline a shader replaces.

    2) Should source code string passed to ShaderSourceARB be null
       terminated?

    DISCUSSION: Source code strings should not be required to end with the
    byte 0. This is a programming language dependent concept, and interferes
    with loading source code out of files. (Memory mapping read-only files
    leaves no ability to add a 0 at the end without an extra copy).
    Development of shaders can be from files, not necessarily from embedded
    source. If null termination was required a shader's source code would be
    read from a file, based on an address and a length, then get copied to
    add a 0 on, then are passed to the compiler which promptly goes and
    finds the 0, in order to get back to an address and a length. That is
    all useless work.

    RESOLUTION: It is allowed, but not required, to have a null termination
    at the end of the string. If the string is null terminated, OpenGL can
    find out the length of the string, and the length parameter passed in
    can be set to negative one.

    3) Should the string passed in to GetUniformLocationARB be null
       terminated?

    DISCUSSION: It is not very likely that this will be a memory mapped
    file, therefore null termination can be assumed.

    RESOLUTION: Yes.

    4) Should the string returned by GetInfoLog be null terminated?

    DISCUSSION: In this case it is useful to have the info string be null
    terminated, so it can be passed to printf() directly. All other strings
    returned by the GL are also null terminated.

    RESOLUTION: YES

    5) Should GetInfoLog also return the length of the string?

    DISCUSSION: This applies to an older version of GetInfoLog, but is no
    longer applicable.

    RESOLUTION: N/A

    6) Do we need a new GLcharARB data type to handle input strings?

    DISCUSSION: Currently there is no precedence of passing in strings into
    OpenGL. This exposes a deficiency in OpenGL data types. In C++ a literal
    string is of type char. OpenGL only has GLubyte and GLbyte data types,
    defined as being unsigned char and signed char respectively. This means
    that it is not possible to pass a literal string to OpenGL using either
    GLubyte or GLbyte. For example, GetUniformLocationARB(programObj,
    "Offset") needs to have the prototype GetUniformLocationARB(handleARB
    obj, const char *string).

    RESOLUTION: YES

    7) Do we load uniforms using their string representation?

    DISCUSSION: Loading uniforms is still performance sensitive, although
    not as much as vertex attributes. Passing in a string into the load
    uniform command seems too big of a performance hit. Every time the load
    is called the string needs to be parsed and the location for the data
    computed. It is better to move this performance cost outside the load
    uniform command into GetUniformLocationARB.

    RESOLUTION: NO.

    8) Should Uniform*ARB take a program object as a parameter?

    DISCUSSION: Again, this is a performance issue. If it does, the object
    passed in needs to be validated for every uniform loaded. Instead, move
    this validation cost outside the uniform command, and have the uniform
    command modify uniforms for the currently in use program object (Set by
    UseProgramObjectARB). The validation cost is now much lower. The program
    object is validated once, when calling UseProgramObjectARB.

    RESOLUTION: NO.

    9) Should uniform values be state per program object?

    DISCUSSION: Should values loaded for uniforms be kept in a program
    object, so that they are retained across program object switches? This
    is application friendly. However, loading uniforms becomes a bit more of
    a heavy weight operation because the OpenGL implementation now has to
    store its values with the program object, and reload when the program
    object is made current, even if the previous program object already had
    the same uniform values loaded.

    RESOLUTION: YES. We don't want to force an application to re-load its
    uniforms every time a program object is used.

    10) Should the name space for uniforms be global per program object?

    DISCUSSION: If one shader object references a uniform called "foo" and
    another shader object, attached to the same program object, also
    references "foo", are those shaders referencing the same uniform? If
    they do not reference the same uniform values, uniforms now need to be
    state per shader object and loaded per shader object. Also, if a vertex
    shader references "foo" and the accompanying fragment shader also
    references "foo", it would make sense to expect those to be the same
    uniform reference.

    RESOLUTION: YES.

    11) What to do if no value is loaded for a uniform?

    DISCUSSION: A program object can be used and rendering commenced without
    loading values for all the uniforms referenced in its shader objects.
    What to do in this case? Note that the values of the uniforms are state
    belonging to the program object. Once loaded, these values are reused
    whenever the program object is in use again. Should uniforms have an
    initial value?

    RESOLUTION: Uniforms are initialized to zero.

    12) Should it be allowed to load uniforms in a display list?

    DISCUSSION: Doing so will make the display list tied to a program
    object. The location passed in to the load uniform commands is program
    object specific. However, this can still be useful for some
    applications. If a program object is in use at CallList time which does
    not match that display list, then all bets are off. See also issue 30.

    RESOLUTION: YES

    13) Do we need uniforms that are local to a program object and uniforms
        that are globally accessible by all program objects?

    DISCUSSION: ARB_vertex_program has this functionality. It seems
    convenient to be able to set a uniform once, and have its value be
    accessible across many shaders (for example, a uniform used to set a
    light position). This type of global uniform could be a performance win
    as well, its value does not have to be cached by OpenGL per program
    object, and re-loaded at every program object switch.

    RESOLUTION: This is useful, but for this version of the spec this
    functionality is deferred.

    14) Do we need INT, FLOAT and BOOL versions of the load uniform
        commands?

    DISCUSSION: There are two types to keep separate. The type the uniform
    is declared in the shader, and the type of the data the application uses
    for uniform values. There are three basic uniform types that can be
    declared in a shader: Float, Int and Bool. Thus one can envision an API
    where the uniform type is encoded in the API name, besides the
    application's data type. For example, UniformInt3iv(). Where the word
    'Int' encodes the uniform type, and 'iv' the user input data type. On
    the other hand, the uniform type information is known to the GL, and
    therefore encoding it in the API name is redundant.

    RESOLUTION: We won't encode the uniform type in the API name.

    15) There is the potential for a huge explosion of load uniform
        commands, what to do?

    DISCUSSION: We need to be able to load a vec1, vec2, vec3, or vec4, or
    arrays of vec1, arrays of vec2, arrays of vec3 or arrays of vec4.
    Furtheremore, there is a need to also load 2x2, 3x3 and 4x4 matrices,
    and arrays of 2x2, arrays of 3x3 and arrays of 4x4 matrices. The input
    values to the load uniforms commands can (traditional OpenGL) come in
    bytes, shorts, ints, floats, doubles and unsigned bytes, unsigned shorts
    and unsigned ints.

    RESOLUTION: A suggested subset is in the New Procedures and Functions
    section below.

    16) Should a special INVALID_HANDLE for the data type handleARB be
        provided, or is 0 sufficient?

    DISCUSSION: 0 is fine. There are less code defects if code compares to
    zero than some invalid handle that is defined to zero anyway.
    Applications should not compare to NULL, since NULL is not necessarily
    defined to be zero in C, only in C++. Besides, a handleARB is an
    integer.

    RESOLUTION: YES.

    17) What happens if the currently in use program object is re-linked by
        calling LinkProgramARB?

    DISCUSSION: Consider that the currently in use program object has a
    uniform named "foo". The application changed some code around in that
    program object, and still has a uniform named "foo", then calls
    LinkProgramARB. After this link call the location of "foo" does not have
    to be the same as before the link call. If LinkProgramARB does not imply
    a call to UseProgramObjectARB, then a call to Uniform*ARB to load a
    value for "foo" is ill defined. In this case, does the application use
    the old location of "foo" or the new location?

    It is consistent with other parts of OpenGL to have updates to an object
    take effect after the update without issuing another command to make the
    update active, for example the TexSubImage* commands.

    RESOLUTION: The re-linked program will be used automatically, without
    requiring a new call to UseProgarmObjectARB.

    18) Should object handles be allocated by the application or by OpenGL?

    DISCUSSION: For current OpenGL objects such as textures and display
    lists, object Ids can be assigned by the application. The Id name space
    is unique for texture objects and display lists. This resulted in a
    different API for generating and managing texture Ids or Display List
    Ids.

    It is not desirable to keep the same mechanism for general object
    management. It prevents the definition of generic operations on objects
    such as deletion and querying. It prevents the OpenGL implementation
    from managing the name space the way it sees fit. It is much more common
    for the underlying library to allocate and manage handles and thereby
    keep control of the name space. It can make using a third party supplied
    library harder or even impossible.

    RESOLUTION: Object handles should be allocated and its name space
    managed by OpenGL, not by the application.

    19) Should a handle be opaque to the application?

    DISCUSSION: A handle is only read and written by OpenGL. Therefore the
    interpretation of the value of the handle does not need to be exposed to
    the application. However, we will expose how a handle is implemented.
    Certain implementation choices for handles, like a pointer, are
    discouraged. The practical solution seems to be to make a handle an
    integer.

    RESOLUTION: YES.

    20) Do we need a way to get the source code back from a shader object?

    DISCUSSION: To stay with the OpenGL philosophy that any state that can
    be set also be queried, we need such a get. This function will return
    the last set of strings stored in a shader object. Note that this set of
    strings is not necessarily the same as the set of strings that compiled
    and linked into program object currently in use.

    RESOLUTION: YES, this is achieved through GetShaderSourceARB.

    21) Are the limits on all resources an executable uses queriable and
        known to the application?

    DISCUSSION: Various proposals have been discussed. One very important
    consideration is to end up with a specification that provides
    application portability (e.g., ISVs do not need to support multiple
    rendering back ends in order to run on all the different flavors of
    hardware). ISVs definitely would prefer the specification to say that
    the OpenGL Shading Language implementation is responsible for ensuring
    that all valid shaders must run.

    RESOLUTION: Resources that are easy to count (number of uniforms
    available to a vertex shader, number of uniforms available to a fragment
    shader, number of vertex attributes, number of varyings, number of
    texture units) will have queriable limits. The application is
    responsible for working within these externally visible limits. The
    OpenGL Shading Language implementation is responsible for virtualizing
    resources that are not easy to count (for example, the number of machine
    instructions in the final executable, number of temporary registers used
    in the final executable, etc.). The expectation is that for any
    practical application an executable (generated by the link stage) will
    run.

    22) Should a higher level shading language be layered on top of OpenGL
        instead of being designed to fit within OpenGL?

    DISCUSSION: In the current design, the OpenGL Shading Language is
    integrated into OpenGL and just provides alternative methods to the
    state controlled pipeline of OpenGL 1.4. The Stanford approach is to
    layer their shading language on top of OpenGL. This has some advantages
    and disadvantages that will become apparent when the differences are
    examined.

    The Stanford approach uses a higher abstraction level. This helps with
    writing some kinds of programs where the abstractions match the problem
    domain. For example treating lights and surfaces as abstract entities
    makes some 3D graphics operations easier, however OpenGL is now being
    used for video and image processing where this abstraction is largely
    irrelevant. Similarly many games have shunned lighting via traditional
    means and use textures (light maps) instead.

    There is nothing in the OpenGL Shading Language or bindings that prevent
    higher levels of abstractions from being layered on top of a
    programmable OpenGL. We also wish to keep the overall abstraction level
    of OpenGL at its current level.

    The Stanford approach also provides for different computational
    frequencies. By having the higher levels of abstraction where one
    program defines the current graphics operation in total allows the
    compiler to separate out the parts that need to run at the primitive
    group level, primitive level, vertex level and fragment level. The
    compiler can therefore generate the code to run on the CPU, vertex
    processor and fragment processor as appropriate. This is obviously more
    complicated to implement than having the programmer specify the programs
    to run on each part of the pipeline (although some hints are still
    required by the Stanford language), although this does make the
    virtualization of the hardware easier as the compiler has the overall
    view.

    The major disadvantage of this is that it forces more intrusive changes
    to OpenGL to support the clear delineation of the primitives, vertices
    and fragment operations. Many of the core OpenGL features have been
    replaced.

    An advantage of the current approach is that the look and feel of OpenGL
    1.4 is maintained and it allows a graceful mix and match approach during
    the transition period from fixed functionality to full programmability.

    This is not a criticism of the Stanford work, as they had no choice but
    to layer on top of OpenGL.

    RESOLUTION: The OpenGL Shading Language should be built into OpenGL, and
    not layered on top. It is also noted that if this is not the case,
    OpenGL should still have a standard shading language.

    23) Should an error be set if a glUseProgramObjectARB call is made on a
        program object that has not been successfully linked?

    DISCUSSION: This was an issue when UseProgramObject returned a Boolean
    indicating success or failure. However, it no longer does, thus an error
    has to be generated.

    RESOLUTION: YES

    24) Do we need a way to get object code back, just like the model of C
        on host processors?

    DISCUSSION: Lots in email on the arb-gl2 mailing list. This is about
    lowest-level, machine specific code that may not even be portable within
    a family of cards from the same vendor. One main goal is to save
    compilation time. There seems to be general consensus that this has
    merit.

    RESOLUTION: This is an interesting capability to have, but will be
    deferred to the next release or could be added as a separate extension.

    25) How are samplers used to access textures?

    DISCUSSION: Samplers are special uniforms used in the OpenGL Shading
    Language to identify the texture object used for each texture lookup.
    The value of a sampler indicates the texture image unit being accessed.
    The type of the sampler identifies the target on that texture image
    unit. The texture object bound to that texture image unit's target is
    then used for the texture lookup. For example, a variable of type
    sampler2D selects target TEXTURE_2D on its texture image unit. Binding
    of texture objects to targets is done as usual with BindTexture.
    Selecting the texture image unit to bind is done as usual with
    ActiveTexture.

    The location of a sampler needs to be queried with
    GetUniformLocationARB, just like any uniform variable, and its value
    needs to be set by calling Uniform1i{v}ARB.

    In the future, sampler types might allow for binding a texture object
    directly, instead of binding to a texture image unit first, to get to a
    texture object.

    RESOLUTION: Resolved

    26) Do we need a validation command as a developers aid?

    DISCUSSION: The LinkProgramARB command will check if the code in all
    shaders in the program object will link. It will catch things like
    having too many active samplers, a mismatch between varyings in a vertex
    and fragment shader, etc. However, it will not check for any errors
    related to the values of uniforms or inconsistent OpenGL state that
    would result in undefined behavior or worse, prevent a program object
    from executing. A validation command could check for things like a
    mismatch between a shadow texture lookup and no TEXTURE_COMPARE_MODE
    set. Or check for values of samplers being out of range. Or check for
    samplers of different types being used to access the same texture image
    unit, etc. This validate command will at least do all the validation
    that needs to occur at render time, and it could do anything extra that
    might help the developer understand their shader(s) better. Note that it
    is not necessary to call validate, it only is a development tool.

    RESOLUTION: YES, this is a desirable feature.

    27) Should there be an info log per object?

    DISCUSSION: To store the info log per object created is consistent with
    the whole object model. However, it might not be useful to keep an info
    log around till the object is deleted. It does take resources away from
    the system. Hence we could keep one info log per object type (shader or
    program objects) as not to take too many resources.

    Alternatively, the specification could say that at least one info log is
    kept per object type, but that the GL implementation is free to keep
    more. This was considered in an earlier version of this specification,
    but broke down when considering the life time of an info log in a
    multi-context situation.

    Note that in either case the API definition for GetInfoLogARB does not
    change. The application passes in a handle for the object, and if the
    info log does not exist it returns an empty string.

    RESOLUTION: We will have an info log per object, and not worry about the
    resource usage.

    28) Is there a need to have a command to append source code to a shader
        object?

    DISCUSSION: AppendShaderARB facilitates applications that generate
    shaders on the fly. Developers can pass parts of a shader source to
    OpenGL this way. However, the application can do the same thing in its
    own memory buffer, and then pass the whole shader to OpenGL using
    ShaderSourceARB. The application usually doesn't have to copy or
    concatenate strings together. It can build a list of strings and pass
    those to OpenGL all at once using ShaderSourceARB.

    RESOLUTION: No, this is deemed not necessary.

    29) Should loading the source code into a shader object automatically
        invoke a compilation?

    DISCUSSION: Keeping the loading of source and compilation of the source
    as two distinctive API commands makes it possible for the application to
    control when an expensive operation like a compile is done. For example,
    it could first load all source for all its shaders at startup, and
    compile them as needed through the execution of the application. Keeping
    it separate leaves the most control to the application.

    RESOLUTION: No.

    30) What happens if an application tries to load more values in a
        uniform than its declared extent?

    DISCUSSION: It is possible to run off the end of a uniform, which could
    potentially corrupt other uniforms, or any data that is stored by OpenGL
    at the position next to the uniform.

    Since it is not known, nor desirable to dictate, where an implementation
    stores its uniforms, it cannot be defined what happens when a load
    uniform command runs off the end. While enforcing bounds checking is
    potentially expensive and can cost a good deal of performance, the
    safety provided by bounds checking is considered more important than the
    highest possible uniform loading performance.

    Note also that the OpenGL Shading Language states that it is undefined
    when a shader references an array element outside the array bounds.

    RESOLUTION: The GL implementation must do whatever bounds checking is
    necessary while loading uniforms. Applications that would like the
    highest API performance should strongly consider using vertex attributes
    for a small number of frequently changing values.

    31) Should UseProgramObjectARB be display-list-able?

    DISCUSSION: Consider a geometric object consisting of multiple
    primitives. The primitives within this geometric object are rendered
    using different shaders. The only way to encapsulate this into one
    display list is by allowing UseProgramObjectARB to be compiled into a
    display list. If this is not allowed, then the geometric object has to
    be broken up in potentially many display lists, creating a management
    nightmare for ISVs.

    ARB_vertex_program allows BindProgramARB to be compiled into a display
    list. Thus when using ARB_vertex_program it is possible to achieve the
    scenario described above.

    UseProgramObjectARB will generate a GL error if its operation failed, so
    that applications can still check if it succeeded.

    RESOLUTION: Yes

    32) Can you explain how uniform loading works?

    DISCUSSION: Uniform variables, including samplers, are named and
    declared in a shader. This name is a string and needs to be used in
    GetUniformLocationARB to retrieve a location ID. Once this location ID
    has been retrieved it won't change until the next call to
    LinkProgramARB. After LinkProgramARB has been issued, the application
    will have to query the location IDs of uniform variables again.
    LinkProgramARB will initialize all uniforms to zero. Note that
    GetUniformLocationARB will only return a location ID if the uniform is
    part of the set of active uniforms, else it will return -1. The set of
    active uniforms, for a given program object, can be queried with
    GetActiveUniformARB.

    Once the location ID is obtained, it can be used in the Uniform*ARB
    commands to load value(s) for the uniform. Note that the Uniform*ARB
    command used has to match the size and the type of the uniform variable.

    GetUniformLocationARB can only retrieve location IDs for uniforms
    declared as a basic type (float, int, bool and vectors thereof) and
    arrays of basic types. It is not possible to query the location ID of a
    structure, for example. The application will have to break down the
    structure into its fields until it has reached a basic type or an array
    of basic type. It does this by using the "." (dot) and "[]" operations
    in the name string passed to GetUniformLocationARB. It is possible to
    query the location ID of an element K in an array. It is possible to use
    that location ID to load multiple values into an array starting at that
    location K. However, it is not possible to take that location ID and add
    an integer N to that location ID to advance to element K + N in that
    array. The application will have to query the location ID of array
    element K + N separately.

    For example, consider the following structure:

    struct {
        struct {
            float a;
            float b[10];
        } c[2];
        vec2 d;
    } e;

    loc1 = GetUniformLocationARB(programObject, "e.d") is a valid command.
    loc2 = GetUniformLocationARB(programObject, "e.c[0]") is not valid.
    loc3 = GetUniformLocationARB(programObject, "e.c[0].b") is a valid command.
    loc4 = GetUniformLocationARB(programObject, "e.c[0].b[2]") is a valid command.

    The location loc2 cannot be retrieved because "e.c[0]" references a
    structure.

    Uniform2fARB(loc1, 1.0f, 2.0f) is a valid command.
    Uniform2iARB(loc1, 1, 2) is not. loc1 references a vec2, not an ivec2.
    Uniform1fARB(loc1, 1.0f) is not. loc1 references a vec2, not a float.
    Uniform1fvARB(loc3, 10, floatPtr) is a valid command.
    Uniform1fvARB(loc4, 10, floatPtr) is not. It runs off the end of the array.
    Uniform1fvARB(loc4, 8, floatPtr) is a valid command.

    RESOLUTION: Yes

    33) Should automatic conversion of input data types be done when loading
        uniforms?

    DISCUSSION: In other words, if the application passes an integer to the
    uniform loading commands, and the uniform is declared as a float, should
    automatic type conversion of that integer to a float occur? The vertex
    attribute loading commands do this, for example.

    OpenGL specifies that this kind of type conversion is dependent on the
    usage of the data. Color, normals and depth components are normalized
    and converted to floats as specified in Table 2.6. Other components are
    not normalized before conversion to float. However, generally it is not
    known what a uniform is used for.

    It is hard to imagine that it is useful for an application to pass in
    data that is declared as a different type in the shader. In that case
    the type of the uniform in the shader could be matched to the
    application's data type instead.

    RESOLUTION: NO. If the basic type of the uniform is float, then
    Uniform*f{v}ARB will have to be used. If the basic type of the uniform
    is integer, then Uniform*i{v}ARB will have to be used. If the basic type
    of the uniform is a sampler, then Uniform1i{v}ARB will have to be used.

    Since there is no Boolean type in C (and we are defining C bindings) but
    there is a Boolean type in the OpenGL Shading Language, type conversion
    needs to be done. It is allowed to either pass in floats or integers if
    the uniform is declared as a boolean. If the basic type of the uniform
    is a Boolean, then either Uniform*f{v}ARB or Uniform*i{v}ARB can be
    used.

    Note that the uniform loading API can later be extended to allow for
    automatic type conversion, with and without normalization, if it turns
    out that is desired.

    34) Why introduce the new terms "Use" and "Create"?

    DISCUSSION: This question refers to glUseProgramObjectARB,
    glCreateShaderObjectARB and glCreateProgramOBjectARB. We could have
    defined glNewShaderObjectARB, glNewProgramObjectARB and left off the
    "Use" in glUseProgramOBjectARB, resulting in glProgramObjectARB.

    RESOLUTION: "New" is used for an existing function name (glNewList) that
    takes a name as input, instead of returning a handle. We deliberately
    chose "Create" for functions that return handles. Similarly "Use" is
    used in a function name that takes a handle as input. Different names
    make it clear to the developer that there are different semantics.

    35) How is a uniform array treated when only some of the array elements
        are actually used?

    DISCUSSION: We have two goals in mind:

      1) To be able to always load a uniform array starting from offset 0
         into the array.
      2) To keep the list of active uniforms as small as possible.

    RESOLUTION: For a uniform array declared in a shader,
    GetActiveUniformARB() will return the name of the array, its basic type
    and a count. This count is determined by the highest element used in the
    shader (as determined by the linker / compiler). If the shader doesn't
    use the array at all, then the GL should obviously not report it as an
    active uniform. Loading more data for the array, using Uniform*ARB, than
    the count returned by GetActiveUniformARB is allowed. The extra data is
    silently ignored (sent to the bit-bucket).

    For example, consider the array:

        uniform vec3 a[10];

    Which is used in a shader that uses elements 3 and 7 in this array.
    GetActiveUniformARB will return:

        "a" - the name of the array
        8 - The size of the array (based on the highest element used, 7)
        FLOAT_VEC3_ARB - The type

    Since array elements 0 through 7 are active, the application can query
    the locations for elements 0, 1, 2, 3, 4, 5, 6, 7 using
    GetUniformLocationARB().

    Loading data for this array using a count of 10 (not 8) is allowed. Thus
    it is legal to issue:

        location = GetUniformLocation(progObj, "a");
        LoadUniform3fv(location, 10, dataPtr);

    This will load data into array elements 0 through 7, since only array
    elements 0 through 7 are active, and will ignore the rest of the data.

    Array data is queried one element at a time. In order to query any
    uniform, a location needs to be provided by the application. Therefore,
    in this example, the application can query data for array elements 0
    through 7, but not for elements 8 and 9.

    This makes array loading portable, independent of the smartness of the
    compiler / linker. It also encourages shader writers to start using
    array elements starting at zero, and work their way upwards, to get
    maximum resource efficiency from the OpenGL implementation. It also
    works nicely with auto-sized uniform arrays (an array declared with
    empty brackets "[]" and indexed only with compile time constants).

    36) Should a location of -1 passed in to Uniform*ARB generate a GL error?

    DISCUSSION: The Uniform*API commands will set an INVALID_OPERATION error
    when passing in a location that does not exist. GetUniformLocationARB
    will return -1 if the string passed in is not an active uniform, or if
    it starts with the prefix "gl_". (This means you cannot get a location
    for active built-in uniforms, for example gl_ModelviewMatrix).

    If you're looping over GetUniformLocationARB and passing the result to
    one of the Uniform*ARB commands, and if any -1 location passed to
    Uniform*ARB will generate a GL error, then this means that you should
    really bracket your Uniform*ARB command with a 'if (location != -1)
    statement. It seems desireable to not generate a GL error when -1 is
    passed in as a location to Uniform*ARB. The data passed in should then
    be silently ignored.

    RESOLUTION. NO. Note that this has changed since the version 0.87 (which
    was published in the extension registry). That version did set an error
    when passing in a location of -1.

    37) What should the behavior of glDeleteObject(0) be?

    DISCUSSION: It would be desirable to allow 0 as a valid input value, and
    not raise an error.

    RESOLUTION: glDeleteObject() will silently ignore deleting the value 0.
    This is consistent with glDeleteTextures() that also silently ignores
    deleting the value 0.

    38) It is unclear how GetUniform*ARB works for matrices. Is the data
        returned in column or row major order?

    DISCUSSION: glGet(MODEL_VIEW_MATRIX) returns data in column major order.
    It was discussed, but rejected, to add two new commands to return
    matrices in column or row major order:

    void GetUniformMatrixfvARB(handleARB programObj, int location,
                               boolean transpose, float *params)
    void GetUniformMatrixivARB(handleARB programObj, int location,
                               boolean transpose, float *params)

    RESOLUTION: GetUniformARB will return data in column major order,
    regardles of the transpose flag used to set the matrix in the
    LoadUniform*ARB commands.

    39) Do "const" qualified variables consume uniform word storage, or not?

    RESOLUTION: They do not.

    40) What happens when a program object currently in use is re-linked,
        and this re-link fails?

    DISCUSSION: This should not affect the executable(s), part of the
    current rendering state. As opposed to revert to fix pipeline for
    example.

    RESOLUTION: The currently active executable code will be kept until
    changed or the program has been linked successfully.

    41) What happens when an empty program object (one with no shader
        objects attached) is linked?

    DISCUSSION: Linking a program object with just a vertex shader will get
    you fixed- function fragment processing. Vice versa, linking a program
    object with just a fragment shader gets you fixed-function vertex
    processing.

    RESOLUTION: This will succeed and in this case you get the fixed
    pipeline for both vertex and fragment processing if UseProgramObject()
    is issued for this program object.

    42) How to indicate the first element of an array when requesting a
        uniform location?

    DISCUSSION: There is a desire to have the location of the first element
    of an array be indicated either using the name of the uniform array, or
    by using the name appended with "[0]".

    That would mean the following:

        uniform s a[1]; // Where 's' is some struct with a field 'f' that is a float.

    The following string combinations could be formed to pass into
    GetUniformLocation:

        a[0].f
        a.f

    If 'f' is an array float f[1] then the following string combinations
    could be formed to pass into GetUniformLocation:

        a[0].f[0]
        a[0].f
        a.f[0]
        a.f

    RESOLUTION: The spec is changed so that in the middle of a string it is
    mandatory to use [0]. Thus that means that only the following two
    strings are valid to pass to GetUniformLocation:

        a[0].f
        a[0].f[0]

    43) What does GetActiveUniformARB() report for the following two
        uniforms?

    DISCUSSION: Consider shader code with:

        uniform float a[1];
        uniform float a;

    The size reported by GetActiveUniformARB() will be '1', and the type
    reported will be float. The string reported can be 'a' in both cases, or
    can be 'a[0]' in the array case. In other words, from this data it is
    not clear to the application if 'a' is an array of size one or a scalar.
    Reporting 'a[0]' is the recommended way for the array case. Technically
    it doesn't really matter, since it is legal to address the first element
    of an array with 'a' or 'a[0]' and pass either string into
    GetUniformLocation.

    RESOLUTION: The GL implementation can report either string. However, it
    is recommended to return 'a[0]'.

    44) Do GL enables affect the built-in state available to a shader?

    DISCUSSION: The lighting state, for example, is still tracked and kept
    current even when lighting, or a specific light, is disabled. This goes
    for all built-in state listed in Chapter 7.5 of the OpenGL Shading
    Language Specification. Do realize that the enables
    VERTEX_PROGRAM_POINT_SIZE and VERTEX_PROGRAM_TWO_SIDE do need to be
    enabled by the application, to get their desired effect.

    RESOLUTION: Enable state is a piece of orthogonal state that is not
    available to a shader. The enable state does not affect the built-in
    state that is available to a shader, which is listed in Chapter 7.5 of
    the OpenGL Shading Language specification.

    45) Please give an example of using the uniform API.

    DISCUSSION: Below are two examples. The first one queries each active
    uniform, then loads a value for it. The second example works of a list
    of uniforms, and queries their locations. Some of the uniforms in that
    list might not be active.

    //
    // Example code that queries active uniforms, then loads their values
    //
    void
    example1(GLhandleARB programObject)
    {
        int    i, count, size, type, linked, location;
        char   uniformName[1000];

        // Link the program object and make sure it succeeded.
        glLinkProgramARB(programObject);
        glGetObjectParameterivARB(programObject, GL_OBJECT_LINK_STATUS_ARB, &linked);

        if (!linked) {
            return;
        }

        // Install the executables in the program object as part of current state.
        glUseProgramObjectARB(programObject);

        // Check for GL Errors

        // Setup uniform values in the array 'colorInterior'.

        // Query the number of active uniforms
        glGetObjectParameterivARB(programObject, GL_OBJECT_ACTIVE_UNIFORMS_ARB,
                                  &count);

        // Loop over each of the active uniforms, and set their value
        for (i = 0; i < count; i++)
        {
            glGetActiveUniformARB(programObject, i, 1000, NULL, &size, &type,
                                  uniformName);
            printf("active uniform: %s\n",uniformName);

            location = glGetUniformLocationARB(programObject, uniformName);

            if (type == GL_FLOAT_VEC3_ARB) {
                float  *data;

                // Allocate data based on 'size'
                // do some kind of hash lookup on the uniform name to get the
                // data to load for the uniform.
                lookupUniformData(uniformName, data);

                // This a vec3, therefore need to use the '3f' or '3fv' version
                // of the uniform loading commands.
                glUniform3fvARB(location, size, data);
            } // else : Setup more types here
        }
    }


    //
    // Example code that has a list of uniforms, and loads values for each uniform
    // in the list. Not all uniforms have to be active ones.
    //
    void
    example2(GLhandleARB programObject)
    {
        int     i, count, linked, location;
        char  **uniformName;
        float  *data;

        // Link the program object and make sure it succeeded.
        glLinkProgramARB(programObject);
        glGetObjectParameterivARB(programObject, GL_OBJECT_LINK_STATUS_ARB, &linked);

        if (!linked) {
            return;
        }

        // Install the executables in the program object as part of current state.
        glUseProgramObjectARB(programObject);

        // Check for GL Errors

        // Setup uniform values in the array 'data'.
        // Setup 'count' and the array 'uniformName'

        // Loop over the list of uniforms in uniformName, and set their value
        for (i = 0; i < count; i++)
        {
            // Location will be -1 if the uniform is not active, but that is OK
            // the uniform loading commands will silently ignore a location of -1.
            location = glGetUniformLocationARB(programObject, uniformName[i]);

            // This a a vec3, therefore need to use the '3f' or '3fv' version of
            // the uniform loading command.
            glUniform3fvARB(location, 1, &data[i * 3]);
        }
    }

    46) Should we add capability to query if an object is dirty?

    DISCUSSION: Specifically, do we add a way to query if a program object
    needs relinking? Do we add a way to query if a shader object needs
    re-compilation?

    RESOLUTION: No, the application can keep track of this information as
    well. Mipmap state consistency is not queriable either, for example.

New Procedures and Functions

    void DeleteObjectARB(handleARB obj)

    handleARB GetHandleARB(enum pname)

    void DetachObjectARB(handleARB containerObj, handleARB attachedObj)

    handleARB CreateShaderObjectARB(enum shaderType)

    void ShaderSourceARB(handleARB shaderObj, sizei count, const charARB **string,
                         const int *length)

    void CompileShaderARB(handleARB shaderObj)

    handleARB CreateProgramObjectARB(void)

    void AttachObjectARB(handleARB containerObj, handleARB obj)

    void LinkProgramARB(handleARB programObj)

    void UseProgramObjectARB(handleARB programObj)

    void ValidateProgramARB(handleARB programObj)

    void Uniform1fARB(int location, float v0)
    void Uniform2fARB(int location, float v0, float v1)
    void Uniform3fARB(int location, float v0, float v1, float v2)
    void Uniform4fARB(int location, float v0, float v1, float v2, float v3)

    void Uniform1iARB(int location, int v0)
    void Uniform2iARB(int location, int v0, int v1)
    void Uniform3iARB(int location, int v0, int v1, int v2)
    void Uniform4iARB(int location, int v0, int v1, int v2, int v3)

    void Uniform1fvARB(int location, sizei count, const float *value)
    void Uniform2fvARB(int location, sizei count, const float *value)
    void Uniform3fvARB(int location, sizei count, const float *value)
    void Uniform4fvARB(int location, sizei count, const float *value)

    void Uniform1ivARB(int location, sizei count, const int *value)
    void Uniform2ivARB(int location, sizei count, const int *value)
    void Uniform3ivARB(int location, sizei count, const int *value)
    void Uniform4ivARB(int location, sizei count, const int *value)

    void UniformMatrix2fvARB(int location, sizei count, boolean transpose, const float *value)
    void UniformMatrix3fvARB(int location, sizei count, boolean transpose, const float *value)
    void UniformMatrix4fvARB(int location, sizei count, boolean transpose, const float *value)

    void GetObjectParameterfvARB(handleARB obj, enum pname, float *params)
    void GetObjectParameterivARB(handleARB obj, enum pname, int *params)

    void GetInfoLogARB(handleARB obj, sizei maxLength, sizei *length, charARB *infoLog)

    void GetAttachedObjectsARB(handleARB containerObj, sizei maxCount, sizei *count,
                              handleARB *obj)

    int GetUniformLocationARB(handleARB programObj, const charARB *name)

    void GetActiveUniformARB(handleARB programObj, uint index, sizei maxLength,
                             sizei *length, int *size, enum *type, charARB *name)

    void GetUniformfvARB(handleARB programObj, int location, float *params)
    void GetUniformivARB(handleARB programObj, int location, int *params)

    void GetShaderSourceARB(handleARB obj, sizei maxLength, sizei *length,
                            charARB *source)

New Tokens

    Accepted by the <pname> argument of GetHandleARB:

        PROGRAM_OBJECT_ARB                              0x8B40

    Accepted by the <pname> parameter of GetObjectParameter{fi}vARB:

        OBJECT_TYPE_ARB                                 0x8B4E
        OBJECT_SUBTYPE_ARB                              0x8B4F
        OBJECT_DELETE_STATUS_ARB                        0x8B80
        OBJECT_COMPILE_STATUS_ARB                       0x8B81
        OBJECT_LINK_STATUS_ARB                          0x8B82
        OBJECT_VALIDATE_STATUS_ARB                      0x8B83
        OBJECT_INFO_LOG_LENGTH_ARB                      0x8B84
        OBJECT_ATTACHED_OBJECTS_ARB                     0x8B85
        OBJECT_ACTIVE_UNIFORMS_ARB                      0x8B86
        OBJECT_ACTIVE_UNIFORM_MAX_LENGTH_ARB            0x8B87
        OBJECT_SHADER_SOURCE_LENGTH_ARB                 0x8B88

    Returned by the <params> parameter of GetObjectParameter{fi}vARB:

        SHADER_OBJECT_ARB                               0x8B48

    Returned by the <type> parameter of GetActiveUniformARB:

        FLOAT                                           0x1406
        FLOAT_VEC2_ARB                                  0x8B50
        FLOAT_VEC3_ARB                                  0x8B51
        FLOAT_VEC4_ARB                                  0x8B52
        INT                                             0x1404
        INT_VEC2_ARB                                    0x8B53
        INT_VEC3_ARB                                    0x8B54
        INT_VEC4_ARB                                    0x8B55
        BOOL_ARB                                        0x8B56
        BOOL_VEC2_ARB                                   0x8B57
        BOOL_VEC3_ARB                                   0x8B58
        BOOL_VEC4_ARB                                   0x8B59
        FLOAT_MAT2_ARB                                  0x8B5A
        FLOAT_MAT3_ARB                                  0x8B5B
        FLOAT_MAT4_ARB                                  0x8B5C
        SAMPLER_1D_ARB                                  0x8B5D
        SAMPLER_2D_ARB                                  0x8B5E
        SAMPLER_3D_ARB                                  0x8B5F
        SAMPLER_CUBE_ARB                                0x8B60
        SAMPLER_1D_SHADOW_ARB                           0x8B61
        SAMPLER_2D_SHADOW_ARB                           0x8B62
        SAMPLER_2D_RECT_ARB                             0x8B63
        SAMPLER_2D_RECT_SHADOW_ARB                      0x8B64

Additions to Chapter 2 of the OpenGL 1.4 Specification (OpenGL Operation)

    Add two new rows to Table 2.2, page 9.

          GL Type     Minimum        Description
                      Bit Width
          -------     -------        -------------
           charARB      8            characters that make up strings
           handleARB    32           identifier for generic objects

    Modify Section 2.5, GL Errors, p. 11

    (modify the last paragraph, p. 11) Four error generation conditions are
    implicit...

    (modify the first paragraph, p. 12) ...the error INVALID_VALUE results.
    Third, the error INVALID_VALUE is generated by any command that takes
    one or more handles as input, and one or more of these handles are not a
    generic object handle generated by OpenGL. Finally, if memory is
    exhausted...

    Modify Section 2.6.1 Begin and End Objects, p. 13

    Remove the term "objects" from this section.

    Add a new section 2.14 Generic Objects, p.60

    The currently existing object types in OpenGL, texture objects (see
    Section 3.8.12) and display lists (see Section 5.4), each have their own
    management API and object ID name space. Rather than designing a new API
    for each new object type added to OpenGL, this section introduces a more
    generic object API, which is initially applied to shader objects
    (Section 2.14.1) and program objects (Section 2.14.2).

    In OpenGL, a "generic object" is an OpenGL-managed opaque data
    structure. The data stored in such a generic object may be quite large,
    so applications are given control over how objects are managed. Generic
    objects are given handles (names) by OpenGL at object creation time.
    Applications can specify the data that is to be stored in objects and
    can modify that data through function calls. Generic objects can be
    created, deleted, modified, attached, detached and used as part of the
    current rendering state.

    Some types of generic objects act as containers for other objects.
    Linking an object to another is called "attaching" and unlinking an
    object is called "detaching".

    To attach an object to a container object, use the command:

        void AttachObjectARB (handleARB containerObj, handleARB obj)

    The error INVALID_OPERATION is generated if <obj> is not a type that can
    be attached to a container object or if <containerObj> is not a
    container object. The same error is generated if an attempt is made to
    attach the same object more than once to the same container object.

    To detach an object from the container object it is attached to, use the
    command:

        void DetachObjectARB(handleARB containerObj, handleARB attachedObj)

    If the object <attachedObj> is not attached to any other container
    object in any rendering context, and the object is flagged for deletion,
    the information for <attachedObj> and the data for <attachedObj> is
    deleted. If <attachedObj> is not attached to <containerObj>, the error
    INVALID_OPERATION is generated. The error INVALID_OPERATION is also
    generated if <containerObj> is not a container object.

    Generic objects can be deleted with the following command:

        void DeleteObjectARB(handleARB obj)

    This command will either delete the object, or flag it for deletion. An
    object that is attached to a container object is not deleted until it is
    no longer attached to any container object, for any context. If it is
    still attached to at least one container object, the object is flagged
    for deletion. If the object is part of the current rendering state, it
    is not deleted until it is no longer part of the current rendering state
    for any context. If the object is still part of the rendering state of
    at least one context, it is flagged for deletion.

    if an object is flagged for deletion, its Boolean status bit
    OBJECT_DELETE_STATUS_ARB is set to true. The value of
    OBJECT_DELETE_STATUS_ARB can be queried with GetObjectParameter{fi}vARB
    (see Section 6.1.12).

    DeleteObjectARB will silently ignore the value zero.

    When a container object is deleted, it will detach each attached object
    as part of the deletion process. When an object is deleted, all
    information for the object referenced is lost. The data for the object
    is also deleted. One bit of state is needed to indicate if a delete
    request for an object was made. The default is no request.

    Add Subsection 2.14.1 Shader Objects

    Subsequent sections of this specification will define stages of the GL
    pipeline that are programmable. The source code that makes up a program
    that gets executed by one of the programmable stages is encapsulated in
    one or more "shader objects". To create a shader object use the
    following command:

        handleARB CreateShaderObjectARB(enum shaderType)

    The shader object is empty when it is created. The <shaderType> argument
    specifies the type of shader object to be created, and should be one of
    < >. (This list to be augmented by other extensions.) If the shader
    object is created successfully, a handle that can be used to reference
    it is returned, and its object specific parameter OBJECT_TYPE_ARB is set
    to SHADER_OBJECT_ARB. The object specific parameter OBJECT_SUBTYPE_ARB
    is set to the actual type of the shader object created. The value of
    OBJECT_TYPE_ARB and OBJECT_SUBTYPE_ARB can be queried with
    GetObjectParameter{fi}vARB (see Section 6.1.12). If the creation failed
    the handle returned will be 0.

    Source code for the shader is specified with the command:

        void ShaderSourceARB(handleARB shaderObj, sizei count,
                             const charARB **string, const int *length)

    The <string> argument is an array of pointers to one or more, optionally
    null terminated, character strings that make up the source code. The
    <length> argument is an array with the number of charARBs in each string
    (the string length). Each element in this array can be set to negative
    one (or smaller), indicating that its accompanying string is null
    terminated. If <length> is set to NULL, all strings in the <string>
    argument are considered null terminated. The ShaderSourceARB command
    sets the source code for the specified shader object <shaderObj> to the
    text strings in the <string> array. If the object previously had source
    code loaded into it, it is completely replaced. The number of strings in
    the array is given in <count>. Any length passed in excludes the null
    termination in its count. If <shaderObj> does not reference a shader
    object, the error INVALID_OPERATION is generated.

    The strings that are loaded into a shader object are expected to form
    the source code for a valid shader as defined in the OpenGL Shading
    Language Specification. Once the source code for a shader has been
    loaded, the shader object can be compiled with the following command:

        void CompileShaderARB(handleARB shaderObj)

    This function will compile <shaderObj>. Each shader object has a Boolean
    status, OBJECT_COMPILE_STATUS_ARB, that is modified as a result of
    compilation. This status can be queried with GetObjectParameter{fi}vARB
    (see Section 6.1.12). This status will be set to TRUE if the shader
    <shaderObj> was compiled without errors and is ready for use, and FALSE
    otherwise. Compilation can fail for a variety of reasons as listed in
    the OpenGL Shading Language Specification. If CompileShaderARB failed,
    any information about a previous compile is lost and is not restored.
    Thus a failed compile does not restore the old state of <shaderObj>. If
    <shaderObj> does not reference a shader object, the error
    INVALID_OPERATION is generated.

    Note that changing the source code of a shader object, through
    ShaderSourceARB, does not change its compile status
    OBJECT_COMPILE_STATUS_ARB.

    Each shader object has an information log that is modified as a result
    of compilation. This information log can be queried with GetInfoLogARB
    to obtain more information about the compilation attempt (see Section
    6.1.12).

    Add Subsection 2.14.2 Program Objects

    The shader objects that are to be used by the programmable stages of
    OpenGL are collected together to form a "program object". The programs
    that are executed by these programmable stages are called "executables".
    All information necessary for defining an executable is encapsulated in
    a program object. A program object is created with the following
    command:

        handleARB CreateProgramObjectARB(void)

    Program objects are empty when they are created. If the program object
    is created successfully, a handle that can be used to reference it is
    returned and its attribute OBJECT_TYPE_ARB is set to PROGRAM_OBJECT_ARB.
    If the creation failed the handle returned will be 0.

    A program object is a container object. Shader objects are attached to a
    program object with the command AttachObjectARB. It is permissible to
    attach shader objects to program objects before source code has been
    loaded into the shader object, or before the shader object has been
    compiled. It is permissible to attach multiple shader objects of the
    same type to a single program object, and it is permissible to attach a
    shader object to more than one program object.

    In order to use the shader objects contained in a program object, the
    program object must be linked. This is accomplished with the following
    command:

        void LinkProgramARB (handleARB programObj)

    This function will link <programObj>. Each program object has a Boolean
    status, OBJECT_LINK_STATUS_ARB, that is modified as a result of linking.
    This status can be queried with GetObjectParameter{fi}vARB (see Section
    6.1.12). This status will be set to TRUE if a valid executable is
    created, and FALSE otherwise. Linking can fail for a variety of reasons
    as specified in the OpenGL Shading Language Specification. Linking will
    also fail if one or more of the shader objects, attached to
    <programObj>, are not compiled successfully, or if more active uniform
    or active sampler variables are used in <programObj> than allowed (see
    Sections 2.14.3 and 2.14.4). If LinkProgramARB failed, any information
    about a previous link is lost and is not restored. Thus a failed link
    does not restore the old state of <programObj>. If <programObj> is not
    of type PROGRAM_OBJECT_ARB, the error INVALID_OPERATION is generated.

    Each program object has an information log that is modified as a result
    of a link operation. This information log can be queried with
    GetInfoLogARB to obtain more information about the link operation (see
    Section 6.1.12).

    If a valid executable is created, it can be made part of the current
    rendering state with the following command:

        void UseProgramObjectARB(handleARB programObj)

    This command will install the executable code as part of current
    rendering state if the program object <programObj> contains valid
    executable code, i.e. has been linked successfully. If
    UseProgramObjectARB is called with the handle set to 0, it is as if the
    GL had no programmable stages and the fixed functionality paths will be
    used instead. If <programObj> cannot be made part of the current
    rendering state, an INVALID_OPERATION error will be generated and the
    current rendering state left unmodified. This error will be set, for
    example, if <programObj> has not been linked successfully. If
    <programObj> is not of type PROGRAM_OBJECT_ARB, the error
    INVALID_OPERATION is generated.

    While a program object is in use, applications are free to modify
    attached shader objects, compile attached shader objects, attach
    additional shader objects, and detach shader objects. This does not
    affect the link status OBJECT_LINK_STATUS_ARB of the program object.
    This does not affect the executable code that is part of the current
    state either. That executable code is only affected when the program
    object has been re-linked successfully. After such a successful re-link,
    the LinkProgramARB command will install the generated executable code as
    part of the current rendering state if the specified program object was
    already in use as a result of a previous call to UseProgramObjectARB. If
    this re-link failed, then the executable code part of the current state
    does not change.

    Add Subsection 2.14.3 Uniform Variables

    Shaders can declare and name "uniform variables" as discussed in the
    OpenGL Shading Language Specification. Values for these uniforms are to
    remain constant over a primitive, and typically they are constant across
    many primitives. Uniforms are program object specific state. They retain
    their values once loaded, and their values are restored whenever a
    program object is used, as long as the program object has not been
    re-linked. A uniform is considered "active" if it is determined by the
    compiler and linker that the uniform will actually be accessed when the
    executable code is executed. In cases where the compiler and linker
    cannot make a conclusive determination, the uniform will be considered
    active.

    As a result of a successful link all active uniforms belonging to the
    program object are initialized to zero. A successful link will also
    generate a location for each active uniform. The values of active
    uniforms can be changed using this location and the appropriate
    Uniform*ARB command (see below). These locations are invalidated and new
    ones assigned after each successful re-link.

    The following function can be used to find the location of an active
    uniform variable within a program object:

        int GetUniformLocationARB(handleARB programObj, const charARB *name)

    This command will return the location of uniform variable <name>. <name>
    has to be a null terminated string, without white space. The value of -1
    will be returned if <name> does not correspond to an active uniform
    variable name in <programObj> or if <name> starts with the reserved
    prefix "gl_". If <programObj> has not been successfully linked, or if
    <programObj> is not of type PROGRAM_OBJECT_ARB, the error
    INVALID_OPERATION is generated. The location of a uniform variable does
    not change until the next link command is issued.

    A valid <name> cannot be a structure, an array of structures, or a
    subcomponent of a vector or a matrix. In order to identify a valid
    <name>, the "." (dot) and "[]" operators can be used in <name> to
    operate on a structure or to operate on an array.

    The first element of a uniform array is identified using the name of the
    uniform array appended with "[0]". Except if the last part of the string
    <name> indicates a uniform array, then the location of the first element
    of that array can be retrieved by either using the name of the uniform
    array, or the name of the uniform array appended with "[0]".

    To determine which of the declared uniform variables are active and to
    determine their sizes and types, use the command:

        void GetActiveUniformARB(handleARB programObj, uint index,
                                 sizei maxLength, sizei *length, int *size,
                                 enum *type, charARB *name)

    This command provides information about the uniform selected by <index>.
    The <index> of 0 selects the first active uniform, and <index> of
    OBJECT_ACTIVE_UNIFORMS_ARB-1 selects the last active uniform. The value
    of OBJECT_ACTIVE_UNIFORMS_ARB can be queried with
    GetObjectParameter{if}vARB (see Section 6.1.12). If <index> is greater
    than or equal to OBJECT_ACTIVE_UNIFORMS_ARB, the error INVALID_VALUE is
    generated.

    The parameter <programObj> is a handle to a program object for which the
    command LinkProgramARB has been issued in the past. It is not necessary
    for <programObj> to have been linked successfully. The link could have
    failed because the number of active uniforms exceeded the limit. If
    <programObj> is not of type PROGRAM_OBJECT_ARB, the error
    INVALID_OPERATION is generated.

    If an error occurred, the return parameters <length>, <size>, <type> and
    <name> will be unmodified.

    For the selected uniform, the uniform name is returned into <name>. The
    string <name> will be null terminated. The actual number of characters
    written by the GL into <name> is returned in <length>. This count
    excludes the null termination. If <length> is NULL then the GL ignores
    this parameter. The maximum number of characters the GL is allowed to
    write into <name> is passed in by <maxLength>. The returned uniform name
    can be the name of built-in uniform state as well. The complete list of
    built-in uniform state is described in section 7.5 of the OpenGL Shading
    Language specification. The length of the longest uniform name in
    <programObj> is given by OBJECT_ACTIVE_UNIFORM_MAX_LENGTH_ARB, which can
    be queried with GetObjectParameter{if}vARB (see Section 6.1.12).

    Each uniform variable, declared in a shader, is broken down into one or
    more strings using the "." (dot) and "[]" operators, if necessary, to
    the point that it is legal to pass each string back into
    GetUniformLocationARB. Each of these strings constitutes one active
    uniform, and each string is assigned an index.

    For the selected uniform, the type of the uniform is returned into
    <type>. The size of the uniform is returned into <size>. The value in
    <size> is in units of the type returned in <type>. The type returned can
    be any of FLOAT, FLOAT_VEC2_ARB, FLOAT_VEC3_ARB, FLOAT_VEC4_ARB, INT,
    INT_VEC2_ARB, INT_VEC3_ARB, INT_VEC4_ARB, BOOL_ARB, BOOL_VEC2_ARB,
    BOOL_VEC3_ARB, BOOL_VEC4_ARB, FLOAT_MAT2_ARB, FLOAT_MAT3_ARB,
    FLOAT_MAT4_ARB, SAMPLER_1D_ARB, SAMPLER_2D_ARB, SAMPLER_3D_ARB,
    SAMPLER_CUBE_ARB, SAMPLER_1D_SHADOW_ARB, SAMPLER_2D_SHADOW_ARB,
    SAMPLER_2D_RECT_ARB or SAMPLER_2D_RECT_SHADOW_ARB.

    If one or more elements of an array are active, GetActiveUniformARB will
    return the name of the array in <name>, subject to the restrictions
    listed above. The type of the array is returned in <type>. The <size>
    parameter contains the highest array element index used, plus one. The
    compiler or linker determines the highest index used. There will be only
    one active uniform reported by the GL per uniform array.

    This command will return as much information about active uniforms as
    possible. If no information is available, <length> will be set to zero
    and <name> will be an empty string. This situation could arise if
    GetActiveUniformARB is issued after a failed link.

    The following commands are used to load values into the uniform
    variables of the program object that is currently in use.

        void Uniform{1234}fARB(int location, T value)
        void Uniform{1234}iARB(int location, T value)

        void Uniform{1234}fvARB(int location, sizei count, T value)
        void Uniform{1234}ivARB(int location, sizei count, T value)

        void UniformMatrix(234}fvARB(int location, sizei count,
                                     boolean transpose, T value)

    These commands will load the given values into the uniform variable
    location identified by <location>.

    The Uniform{1234}f{v}ARB commands will load one or more floating-point
    values <count> times into a uniform location defined as a float or
    floating-point vector or an array of floats or an array of
    floating-point vectors.

    The Uniform{1234}i{v}ARB commands will load one or more integer values
    <count> times into a uniform location defined as a sampler, integer or
    integer vector or an array of integers or an array of integer vectors.
    Only the Uniform1i{v}ARB commands can be used to load sampler values.
    See section 2.14.4.

    The UniformMatrix{234}fvARB commands will load a 2x2, 3x3 or 4x4 matrix
    (corresponding to 2, 3, or 4 in the command name) of floating-point
    values <count> times into a uniform location defined as a matrix or an
    array of matrices. If <transpose> is FALSE, the matrix is specified in
    column major order, otherwise in row major order.

    When loading values for a uniform declared as a Boolean, a Boolean
    vector or an array of Booleans or an array of Boolean vectors, both the
    Uniform*i{v} and Uniform*f{v} set of commands can be used to load
    Boolean values. Type conversion is done by the GL. The uniform is set to
    FALSE if the input value is 0 or 0.0f, and set to TRUE otherwise. The
    Uniform*ARB command used must match the size of the uniform, as declared
    in the shader. For example, to load a uniform declared as a bvec2,
    either Uniform2i{v}ARB or Uniform2f{v}ARB can be used. An
    INVALID_OPERATION error will be generated if an attempt is made to use a
    non-matching Uniform*ARB command. In this example using Uniform1ivARB
    would generate an error.

    For all other uniform types the Uniform*ARB command used must match the
    size and type of the uniform, as declared in the shader. No type
    conversions are done. For example, to load a uniform declared as a vec4,
    Uniform4f{v}ARB must be used. To load a 3x3 matrix,
    UniformFloatMatrix3fvARB must be used. An INVALID_OPERATION error will
    be generated if an attempt is made to use a non-matching Uniform*ARB
    command. In this example, using Uniform4i{v}ARB would generate an error.

    When loading N elements starting at an arbitrary position k in a uniform
    declared as an array, elements k through k + N - 1 in the array will be
    replaced with the new values. Values for any array element that exceeds
    the highest array element index used, as reported by
    GetActiveUniformARB, will be ignored by the GL.

    If the value of <location> is -1, the Uniform*ARB commands will silently
    ignore the data passed in. The current uniform values will therefore not
    be changed.

    The following applies to errors that can be generated when loading
    uniforms:

      - If the size indicated in the name of the Uniform*ARB command used
        does not match the size of the uniform declared in the shader, an
        INVALID_OPERATION error is generated and the uniform's value is not
        changed.
      - If a uniform not of type Boolean is loaded, then if the type
        indicated in the name of the Uniform*ARB command used does not match
        the type of the uniform declared in the shader, an INVALID_OPERATION
        error is generated and the uniform's value is not changed.
      - If <location> is not -1 and <location> does not exist for the program
        object currently in use, the error INVALID_OPERATION is generated.
      - The error INVALID_OPERATION is generated by any of the Uniform*ARB
        commands if there is no program object in use.

    Add Subsection 2.14.4 Samplers

    Samplers are special uniforms used in the OpenGL Shading Language to
    identify the texture object used for each texture lookup. The value of a
    sampler indicates the texture image unit being accessed. Setting a
    sampler's value to i selects texture image unit number i. The values of
    i range from zero to the maximum supported number of texture image
    units. This maximum is implementation dependent, and defined in other
    specifications.

    The type of the sampler identifies the target on the texture image unit.
    The texture object bound to that texture image unit's target is then
    used for the texture lookup. For example, a variable of type sampler2D
    selects target TEXTURE_2D on its texture image unit. Binding of texture
    objects to targets is done as usual with BindTexture. Selecting the
    texture image unit to bind to is done as usual with ActiveTexture.

    The location of a sampler needs to be queried with
    GetUniformLocationARB, just like any uniform variable. Sampler values
    need to be set by calling Uniform1i{v}ARB. Loading samplers with any of
    the other Uniform*ARB entry points is not allowed and will result in an
    INVALID_OPERATION error.

    It is not allowed to have variables of different sampler types pointing
    to the same texture image unit within a program object. This situation
    can only be detected at the next rendering command issued, and an
    INVALID_OPERATION error will then be generated.

    Active samplers are samplers actually being used in a program object.
    The LinkProgramARB command determines if a sampler is active or not. The
    LinkProgramARB command will attempt to determine if the active samplers
    in the shader(s) contained in the program object exceed the maximum
    allowable limits. If it determines that the count of active samplers
    exceeds the allowable limits, then the link fails. (These limits are
    determined by other extensions, and can be different for different types
    of shaders.) If this cannot be determined at link time, for example if
    the program object only contains a vertex shader, then this will be
    determined at the next rendering command issued, and an
    INVALID_OPERATION error will then be generated.

    Add Subsection 2.14.5 Resource Limits

    A shader should not fail to compile and a program object to link due to
    lack of instruction space or lack of temporary variables.
    Implementations should ensure that all valid shaders and program objects
    could be successfully compiled, linked and executed.

    Add Subsection 2.15 Validation

    It is not always possible to determine at link time if a program object
    actually will execute. Therefore validation is done when the first
    rendering command is issued, to determine if the currently active
    program object can be executed. If it cannot be executed then no
    fragments will be rendered, and Begin, RasterPos, or any command that
    performs an explicit Begin will generate the error INVALID_OPERATION.

    This error is generated by Begin, RasterPos, or any command that
    performs an explicit Begin if:

      * One or more samplers of different types in the current program
        object access the same texture image unit.
      * If more than the maximum allowable texture image units are accessed
        based on the count of active samplers and the rest of the GL state.
        Note that LinkProgramARB can normally resolve this, except for the
        case where an ARB_vertex_shader shader is mixed with an
        ARB_fragment_program shader or mixed with fixed-function fragment
        processing.

    The INVALID_OPERATION error reported by these rendering commands does
    not provide enough information to find out why the currently active
    program object would not execute. No information at all is available
    about a program object that would still execute, but is inefficient or
    sub optimal given the current GL state. As a development aid, use the
    command

        void ValidateProgramARB(handleARB programObj)

    to validate the program object <programObj> against the GL state at that
    moment. Each program object has a Boolean status,
    OBJECT_VALIDATE_STATUS_ARB, that is modified as a result of validation.
    This status can be queried with GetObjectParameter{if}vARB (see Section
    6.1.12). If validation succeeded this status will be set to TRUE,
    otherwise it will be set to FALSE. If validation succeeded the program
    object is guaranteed to execute, given the current GL state. If
    validation failed, the program object is guaranteed to not execute,
    given the current GL state. If <programObj> is not of type
    PROGRAM_OBJECT_ARB, the error INVALID_OPERATION is generated.

    ValidateProgramARB will validate at least as much as is done when a
    rendering command is issued, and it could validate more. For example, it
    could give a hint on how to optimize some piece of shader code.

    ValidateProgramARB will store its information in the info log. This
    information will either be an empty string or it will contain validation
    information.

    ValidateProgramARB is typically only useful during application
    development. An application should not expect different OpenGL
    implementations to produce identical information.

    2.16 Undefined Behavior

    By addressing arrays or matrices in a shader it is possible to index
    outside the declared extent of a uniform. Thus it could be possible to
    overwrite critical GL data that is stored next to the uniform in memory.
    What this data could be is GL implementation specific. The OpenGL
    Shading Language states that it is undefined what happens in this case.

    The system environment the OpenGL implementation runs in can set certain
    rules, or good practices, that restrict certain behavior. For example,
    on a modern OS it is not allowed to overwrite data in someone else's
    address space. Similarly it would therefore not be allowed to overwrite
    GL data that belongs to another process. This could be further
    restricted by disallowing the ability to overwrite data belonging to
    another context within the same process. The GL implementation, in
    combination with the system environment, decides what is acceptable
    behavior; hence the specification leaves results undefined.

    2.17 Required State

    The state required to support shader objects consists of:

      * The state that must be maintained to indicate which handles are
        currently in use as shader object names.

    The state required per shader object consists of:

      * A handleARB indicating the shader object name.
      * An array of arrays of type charARB containing the shader strings,
        initially empty.
      * An integer holding the length of the concatenation of the shader
        strings, including one null termination.
      * An array of unsigned integers holding the length of the shader
        strings, initially zero.
      * An integer holding the value of OBJECT_TYPE_ARB
      * An integer holding the value of OBJECT_SUBTYPE_ARB
      * A Boolean holding the status of the last compile.
      * A Boolean holding the delete status.
      * An array of type charARB containing the info log, initially empty.
      * An integer holding the length of the info log, including a null
        termination.

    Initially, no shader objects exist.

    The state required to support program objects consists of:

      * The state that must be maintained to indicate which handles are
        currently in use as program object names.
      * One handleARB to store the handle of the program object currently in
        use.

    The state required per program object consists of:

      * A handleARB indicating the program object object name.
      * A list of handleARB to keep track of shader objects attached.
      * An integer holding the number of attached shader objects.
      * A Boolean indicating if the program object has been successfully
        linked.
      * A Boolean holding the status of the last validation attempt.
      * A Boolean holding the delete status.
      * An integer holding the value of OBJECT_TYPE_ARB.
      * An array of type charARB containing the info log, initially empty.
      * An integer holding the length of the info log, including a null
        termination.
      * An array of type charARB for each active uniform containing its
        name, initially empty.
      * An integer holding the length of the longest active uniform name,
        including a null termination.
      * An integer holding the number of active uniforms.
      * An integer for each active uniform, containing its size.
      * An integer for each active uniform, containing its type.
      * An integer for each active uniform, holdings its location.

    Initially, no program objects exist.

Additions to Chapter 3 of the OpenGL 1.4 Specification (Rasterization)

        None

Additions to Chapter 4 of the OpenGL 1.4 Specification (Per-Fragment
Operations and the Frame Buffer)

        None

Additions to Chapter 5 of the OpenGL 1.4 Specification (Special Functions)

    Add to section 5.4, Display Lists.

    Commands that are used to create and manage objects are not included in
    display lists, but are executed immediately. These include
    DeleteObjectARB, DetachObjectARB, CreateShaderObjectARB,
    ShaderSourceARB, CompileShaderARB, CreateProgramObjectARB,
    AttachObjectARB, and LinkProgramARB.

    Commands that are used to query various pieces of object state are not
    included in display lists, but are executed immediately. These include
    GetHandleARB, GetObjectParameterfvARB, GetObjectParameterivARB,
    GetInfoLogARB, GetUniformfvARB, GetUniformivARB, GetUniformLocationARB,
    GetShaderSourceARB, GetActiveUniformARB, GetAttachedObjectsARB and
    ValidateProgramARB.

Additions to Chapter 6 of the OpenGL 1.4 Specification (State and State Requests)

    Add a new section just after section 6.1.11 (p. 214) called 6.1.12
    "Generic Object Queries" and renumber section 6.1.12 as 6.1.13.

    The command

        handleARB GetHandleARB(enum pname)

    returns the handle to an object that is in use as part of current state.
    <pname> specifies the state item for which the current object is to be
    returned and can be one of PROGRAM_OBJECT_ARB. (This list is augmented
    by other extensions.) If <pname> is not a valid state item, 0 is
    returned.

    The commands

        void GetObjectParameterfvARB(handleARB obj, enum pname, float *params)
        void GetObjectParameterivARB(handleARB obj, enum pname, int *params)

    return object specific parameter values for object <obj> in <params>.
    The parameter value to return is specified by <pname>.

    If <pname> is OBJECT_TYPE_ARB, GetObjectParameter{if}vARB returns
    PROGRAM_OBJECT_ARB if <obj> references a program object. It returns
    SHADER_OBJECT_ARB if <obj> references any shader object. If <obj> is not
    of type PROGRAM_OBJECT_ARB or SHADER_OBJECT_ARB, the error
    INVALID_OPERATION is generated.

    If <pname> is OBJECT_SUBTYPE_ARB, GetObjectParameter{if}vARB returns the
    subtype of a shader object. If <obj> is not of type SHADER_OBJECT_ARB,
    the error INVALID_OPERATION is generated.

    If <pname> is OBJECT_DELETE_STATUS_ARB, GetObjectParameter{if}vARB
    returns 1 or 1.0f if status is TRUE and 0 or 0.0f if status is FALSE. If
    <obj> is not of type PROGRAM_OBJECT_ARB or SHADER_OBJECT_ARB, the error
    INVALID_OPERATION is generated.

    If <pname> is OBJECT_LINK_STATUS_ARB, GetObjectParameter{if}vARB returns
    1 or 1.0f if status is TRUE and 0 or 0.0f if status is FALSE. If <obj>
    is not of type PROGRAM_OBJECT_ARB, the error INVALID_OPERATION is
    generated.

    If <pname> is OBJECT_VALIDATE_STATUS_ARB, GetObjectParameter{if}vARB
    returns 1 or 1.0f if status is TRUE and 0 or 0.0f if status is FALSE. If
    <obj> is not of type PROGRAM_OBJECT_ARB, the error INVALID_OPERATION is
    generated.

    If <pname> is OBJECT_COMPILE_STATUS_ARB, GetObjectParameter{if}vARB
    returns 1 or 1.0f if status is TRUE and 0 or 0.0f if status is FALSE. If
    <obj> is not of type SHADER_OBJECT_ARB, the error INVALID_OPERATION is
    generated.

    If <pname> is OBJECT_INFO_LOG_LENGTH_ARB, GetObjectParameter{if}vARB
    returns the length of the info log, including a null termination. If
    there is no info log, 0 or 0.0f is returned. If <obj> is not of type
    PROGRAM_OBJECT_ARB or SHADER_OBJECT_ARB, the error INVALID_OPERATION is
    generated.

    If <pname> is OBJECT_ATTACHED_OBJECTS_ARB, GetObjectParameter{if}vARB
    returns the number of objects attached. If no objects are attached, 0 or
    0.0f is returned. If <obj> is not of type PROGRAM_OBJECT_ARB the error
    INVALID_OPERATION is generated.

    If <pname> is OBJECT_ACTIVE_UNIFORMS_ARB, GetObjectParameter{if}vARB
    returns the number of active uniforms. If no active uniforms exist, 0 or
    0.0f is returned. If <obj> is not of type PROGRAM_OBJECT_ARB the error
    INVALID_OPERATION is generated.

    If <pname> is OBJECT_ACTIVE_UNIFORM_MAX_LENGTH_ARB,
    GetObjectParameter{if}vARB returns the length of the longest active
    uniform name, including a null termination. If no active uniforms exist,
    0 or 0.0f is returned. If <obj> is not of type PROGRAM_OBJECT_ARB the
    error INVALID_OPERATION is generated.

    If <pname> is OBJECT_SHADER_SOURCE_LENGTH_ARB,
    GetObjectParameter{if}vARB returns the length of the concatenation of
    the source strings making up the shader source, including a null
    termination. If no source exists, 0 or 0.0f is returned. If <obj> is not
    of type SHADER_OBJECT_ARB the error INVALID_OPERATION is generated.

    If an error occurred, the return parameter <params> will be unmodified.

    The command

        void GetAttachedObjectsARB(handleARB containerObj, sizei maxCount,
                                   sizei *count, handleARB *obj)

    returns the handles of objects attached to <containerObj> in <obj>. The
    actual number of object handles written by the GL into <obj> is returned
    in <count>. If no objects are attached, <count> is set to zero. If
    <count> is NULL then the GL ignores this parameter. The maximum number
    of handles the GL is allowed to write into <obj> is passed in by
    <maxCount>. The number of objects attached to <containerObj> is given by
    OBJECT_ATTACHED_OBJECTS_ARB, which can be queried with
    GetObjectParameter{if}vARB. If <containerObj> is not of type
    PROGRAM_OBJECT_ARB, the error INVALID_OPERATION is generated. If an
    error occurred, the return parameters <count> and <obj> will be
    unmodified.

    A string that contains information about the last link or validation
    attempt and last compilation attempt are kept per program or shader
    object. This string is called the info log and can be obtained with the
    command:

        void GetInfoLogARB(handleARB obj, sizei maxLength, sizei *length,
                           charARB *infoLog)

    This command returns the info log string in <infoLog>. This string will
    be null terminated. The actual number of characters written by the GL
    into <infoLog> is returned in <length>, excluding the null termination.
    If <length> is NULL then the GL ignores this parameter. The maximum
    number of characters the GL is allowed to write into <infoLog> is passed
    in by <maxLength>. The number of characters in the info log is given by
    OBJECT_INFO_LOG_LENGTH_ARB, which can be queried with
    GetObjectParameter{fi}vARB. If <obj> is a shader object, the returned
    info log will either be an empty string or it will contain information
    about the last compilation attempt for that object. If <obj> is a
    program object, the returned info log will either be an empty string or
    it will contain information about the last link attempt or last
    validation attempt for that object. If <obj> is not of type
    PROGRAM_OBJECT_ARB or SHADER_OBJECT_ARB, the error INVALID_OPERATION is
    generated. If an error occurred, the return parameters <length> and
    <infoLog> will be unmodified.

    The info log is typically only useful during application development and
    an application should not expect different OpenGL implementations to
    produce identical info logs.

    The command

        void GetShaderSourceARB(handleARB obj, sizei maxLength,
                                sizei *length, charARB *source)

    will return in <source> the string making up the source code for the
    shader object <obj>. The string <source> will be null terminated. The
    actual number of characters written by the GL into <source> is returned
    in <length>, excluding the null termination. If <length> is NULL then
    the GL ignores this parameter. The maximum number of characters the GL
    is allowed to write into <source> is passed in by <maxLength>. The
    string <source> is a concatenation of the strings passed to OpenGL using
    ShaderSourceARB. The length of this concatenation is given by
    OBJECT_SHADER_SOURCE_LENGTH_ARB, which can be queried with
    GetObjectParameter{if}vARB. If <obj> is not of type SHADER_OBJECT_ARB,
    the error INVALID_OPERATION is generated. If an error occurred, the
    return parameters <length> and <source> will be unmodified.

    The commands

        void GetUniformfvARB(handleARB programObj, int location, float *params)
        void GetUniformivARB(handleARB programObj, int location, int *params)

    return the value or values of the uniform at location <location> for
    program object <programObj> in the array <params>. The type of the
    uniform at <location> determines the number of values returned. The
    error INVALID_OPERATION is generated if <programObj> is not of type
    PROGRAM_OBJECT_ARB or if <programObj> has not been linked successfully
    or if <location> is not a valid location for <programObj>. In order to
    query the values of an array of uniforms a GetUniform*ARB command needs
    to be issued for each array element. If the uniform queried is a matrix,
    the values of the matrix are returned in column major order. If an error
    occurred, the return parameter <params> will be unmodified.

    Add to Table 6.3: State Variable Types (p. 217)

        H    Object handle

Additions to Appendix A of the OpenGL 1.4 Specification (Invariance)

        None

Additions to the AGL/GLX/WGL Specifications

    Analogous to sharing display lists and texture objects, it is possible
    to share the name space for handles for all objects across a set of
    contexts, as long as the server sides of the contexts share the same
    address space. No change is made to the AGL/GLX/WGL API. If handles are
    shared across contexts the data belonging to those objects are shared as
    well. Changes to objects shared between multiple rendering contexts will
    be serialized (i.e., the changes will occur in a specific order).

    Changes to a program object made by one rendering context are not
    guaranteed to take effect in another rendering context until the other
    calls UseProgramObjectARB for that object.

    When a program object is deleted by one rendering context, the object
    itself is not destroyed until it is no longer the current program object
    in any context.

    When a shader object is deleted by one rendering context, the object
    itself is not destroyed until it is no longer attached to any program
    object in any context.

GLX Protocol

    The following rendering commands are sent to the server as part of a
    glXRender request:

    DeleteObjectARB

        2           8                rendering command length
        2           238              rendering command opcode
        4           CARD32           obj

    DetachObjectARB

        2           12               rendering command length
        2           239              rendering command opcode
        4           CARD32           containerObj
        4           CARD32           attachedObj

    CompileShaderARB

        2           8                rendering command length
        2           240              rendering command opcode
        4           CARD32           shaderObj

    AttachObjectARB

        2           12               rendering command length
        2           241              rendering command opcode
        4           CARD32           containerObj
        4           CARD32           obj

    LinkProgramARB

        2           8                rendering command length
        2           242              rendering command opcode
        4           CARD32           programObj
    
    UseProgramObjectARB

        2           8                rendering command length
        2           243              rendering command opcode
        4           CARD32           programObj

    ValidateProgramARB

        2           8                rendering command length
        2           244              rendering command opcode
        4           CARD32           programObj

    Uniform1fARB

        2           12               rendering command length
        2           245              rendering command opcode
        4           INT32            location
        4           FLOAT32          v0

    Uniform2fARB

        2           16               rendering command length
        2           246              rendering command opcode
        4           INT32            location
        4           FLOAT32          v0
        4           FLOAT32          v1

    Uniform3fARB

        2           20               rendering command length
        2           247              rendering command opcode
        4           INT32            location
        4           FLOAT32          v0
        4           FLOAT32          v1
        4           FLOAT32          v2

    Uniform4fARB
        2           24               rendering command length
        2           248              rendering command opcode
        4           INT32            location
        4           FLOAT32          v0
        4           FLOAT32          v1
        4           FLOAT32          v2
        4           FLOAT32          v3

    Uniform1iARB

        2           12               rendering command length
        2           249              rendering command opcode
        4           INT32            location
        4           INT32            v0 

    Uniform2iARB

        2           16               rendering command length
        2           250              rendering command opcode
        4           INT32            location
        4           INT32            v0
        4           INT32            v1

    Uniform3iARB

        2           20               rendering command length
        2           251              rendering command opcode
        4           INT32            location
        4           INT32            v0
        4           INT32            v1
        4           INT32            v2

    Uniform4iARB

        2           24               rendering command length
        2           252              rendering command opcode
        4           INT32            location
        4           INT32            v0
        4           INT32            v1
        4           INT32            v2
        4           INT32            v3

    The following rendering commands are sent to the server as part of a
    glXRender request or as a glXRenderLarge request:

    ShaderSourceARB

        2           12+(count*4)+n+p rendering command length
        2           253              rendering command opcode
        4           CARD32           shaderObj
        4           CARD32           count
        4*count     LISTofINT32      length
        n           LISTofBYTE       string.  n is described below
        p                            unused, p=pad(n)

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           16+(count*4)+n+p rendering command length
        4           253              rendering command opcode

    n is the sum of the length of all the strings in the array passed
    in as <string>.  The length of each string i, where i = [0, <count>),
    is strlen(<string[i]>) if <length> is NULL or if <length[i]> is
    negative.  Otherwise, the length of string i is <length[i]>.  If
    <count> is 0, n is 0.

    Uniform1fvARB

        2           12+count*4       rendering command length
        2           254              rendering command opcode
        4           INT32            location
        4           CARD32           count
        4*count     LISTofFLOAT32    value

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           16+count*4       rendering command length
        4           254              rendering command opcode

    Uniform2fvARB

        2           12+count*4*2     rendering command length
        2           255              rendering command opcode
        4           INT32            location
        4           CARD32           count
        4*count*2   LISTofFLOAT32    value

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           16+count*4*2     rendering command length
        4           255              rendering command opcode

    Uniform3fvARB

        2           12+count*4*3     rendering command length
        2           256              rendering command opcode
        4           INT32            location
        4           CARD32           count
        4*count*3   LISTofFLOAT32    value

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           16+count*4*3     rendering command length
        4           256              rendering command opcode

    Uniform4fvARB

        2           12+count*4*4     rendering command length
        2           257              rendering command opcode
        4           INT32            location
        4           CARD32           count
        4*count*4   LISTofFLOAT32    value

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           16+count*4*4     rendering command length
        4           257              rendering command opcode

    Uniform1ivARB

        2           12+count*4       rendering command length
        2           258              rendering command opcode
        4           INT32            location
        4           CARD32           count
        4*count     LISTofINT32      value

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           16+count*4       rendering command length
        4           258              rendering command opcode

    Uniform2ivARB

        2           12+count*4*2     rendering command length
        2           259              rendering command opcode
        4           INT32            location
        4           CARD32           count
        4*count*2   LISTofINT32      value

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           16+count*4*2     rendering command length
        4           259              rendering command opcode

    Uniform3ivARB

        2           12+count*4*3     rendering command length
        2           260              rendering command opcode
        4           INT32            location
        4           CARD32           count
        4*count*3   LISTofINT32      value

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           16+count*4*3     rendering command length
        4           260              rendering command opcode

    Uniform4ivARB

        2           12+count*4*4     rendering command length
        2           261              rendering command opcode
        4           INT32            location
        4           CARD32           count
        4*count*4   LISTofINT32      value

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           16+count*4*4     rendering command length
        4           261              rendering command opcode

    UniformMatrix2fvARB

        2           16+4*count*2*2   rendering command length
        2           262              rendering command opcode
        4           INT32            location
        4           CARD32           count
        1           CARD8            transpose
        3           CARD8            unused
        4*count*2*2 LISTofFLOAT32    value

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           20+4*count*2*2   rendering command length
        4           262              rendering command opcode

    UniformMatrix3fvARB

        2           16+4*count*3*3   rendering command length
        2           263              rendering command opcode
        4           INT32            location
        4           CARD32           count
        1           CARD8            transpose
        3           CARD8            unused
        4*count*3*3 LISTofFLOAT32    value

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           20+4*count*3*3   rendering command length
        4           263              rendering command opcode

    UniformMatrix4fvARB

        2           16+4*count*4*4   rendering command length
        2           264              rendering command opcode
        4           INT32            location
        4           CARD32           count
        1           CARD8            transpose
        3           CARD8            unused
        4*count*4*4 LISTofFLOAT32    value

    If the command is encoded in a glXRenderLarge request, the
    command opcode and command length fields above are expanded to
    4 bytes each:

        4           20+4*count*4*4   rendering command length
        4           264              rendering command opcode


    The following non-rendering commands are added.

    GetHandleARB

        1           CARD8            opcode (X assigned)
        1           167              GLX opcode
        2           3                request length
        4           GLX_CONTEXT_TAG  context tag
        4           ENUM             pname
      =>
        1           1                reply
        1                            unused
        2           CARD16           sequence number
        4           0                reply length
        4           CARD32           return value
        20                           unused

    CreateShaderObjectARB

        1           CARD8            opcode (X assigned)
        1           168              GLX opcode
        2           3                request length
        4           GLX_CONTEXT_TAG  context tag
        4           ENUM             shaderType
      =>
        1           1                reply
        1                            unused
        2           CARD16           sequence number
        4           0                reply length
        4           CARD32           return value
        20                           unused

    CreateProgramObjectARB

        1           CARD8            opcode (X assigned)
        1           169              GLX opcode
        2           2                request length
        4           GLX_CONTEXT_TAG  context tag
      =>
        1           1                reply
        1                            unused
        2           CARD16           sequence number
        4           0                reply length
        4           CARD32           return value
        20                           unused

    GetObjectParameterfvARB

        1           CARD8            opcode (X assigned)
        1           170              GLX opcode
        2           4                request length
        4           GLX_CONTEXT_TAG  context tag
        4           CARD32           obj
        4           ENUM             pname
      =>
        1           1                reply
        1                            unused
        1           CARD16           sequence number 
        4           m                reply length, m = ((n == 1) ? 0 : n)
        4                            unused
        4           CARD32           n

        if (n = 1) this follows:

        4           FLOAT32          params
        12                           unused

        otherwise this follows:

        16                           unused
        n*4         LISTofFLOAT32    params

    Note that n may be zero, indicating that a GL error occured.

    GetObjectParameterivARB

        1           CARD8            opcode (X assigened)
        1           171              GLX opcode
        2           4                request length
        4           GLX_CONTEXT_TAG  context tag
        4           CARD32           obj
        4           ENUM             pname
      =>
        1           1                reply
        1                            unused
        2           CARD16           sequence number 
        4           m                reply length, m = ((n == 1) ? 0 : n)
        4                            unused
        4           CARD32           n

        if (n = 1) this follows:

        4           INT32            params
        12                           unused

        otherwise this follows:

        16                           unused
        n*4         LISTofINT32      params

    Note that n may be zero, indicating that a GL error occured.

    GetInfoLogARB

        1           CARD8            opcode (X assigned)
        1           172              GLX opcode
        2           4                request length
        4           GLX_CONTEXT_TAG  context tag
        4           CARD32           obj
        4           CARD32           maxLength
      =>
        1           1                reply
        1                            unused
        2           CARD16           sequence number
        4           m                reply length, m = (n+p)/4
        4                            unused
        4           CARD32           n, as defined below.
        16                           unused
        n           LISTofBYTE       infoLog
        p                            unused, p = pad(n)

    n is calculated on the server as strlen(<infoLog>) + 1 on success, or
    0 if there was an error retrieving the info log.  If <length> is not
    NULL, it is set to max(1, n) - 1.

    GetAttachedObjectsARB

        1           CARD8            opcode (X assigned)
        1           173              GLX opcode
        2           4                request length
        4           GLX_CONTEXT_TAG  context tag
        4           CARD32           containerObj
        4           CARD32           maxCount
      =>
        1           1                reply
        1                            unused
        2           CARD16           sequence number
        4           m                reply length, m = (n == 1 ? 0 : n)
        4                            unused
        4           CARD32           count, n = count

        if (n = 1) this follows:

        4           CARD32           obj
        12                           unused

        otherwise this follows:

        16                           unused
        4*n         LISTofCARD32     obj

    Note that n may be zero, indicating that a GL error occured.

    GetUniformLocationARB
        1           CARD8            opcode (X assigned)
        1           174              GLX opcode
        2           (12+n+p)/4       request length
        4           GLX_CONTEXT_TAG  context tag
        4           CARD32           programObj
        n           LISTofBYTE       name, n = strlen(name)+1
        p                            unused, p = pad(n)
      =>
        1           1                reply
        1                            unused
        2           CARD16           sequence number
        4           0                reply length
        4           CARD32           return value
        20                           unused

    GetActiveUniformARB

        1           CARD8            opcode (X assigned)
        1           175              GLX opcode
        2           5                request length
        4           GLX_CONTEXT_TAG  context tag
        4           CARD32           programObj
        4           CARD32           index
        4           CARD32           maxLength
      =>
        1           1                reply
        1                            unused
        2           CARD16           sequence number
        4           m                reply length, m = (n+p)/4
        4                            unused
        4           CARD32           n, n = length+1
        4           CARD32           size
        4           ENUM             type
        8                            unused
        n           LISTofBYTE       name
        p                            unused , p = pad(n)

    n is calculated on the server as strlen(<name>) + 1 on success, or 0
    if there was an error retrieving the active uniform's name.  If
    <length> is not NULL, it is set to max(1, n) - 1.

    GetUniformfvARB

        1           CARD8            opcode (X assigned)
        1           176              GLX opcode
        2           4                request length
        4           GLX_CONTEXT_TAG  context rag
        4           CARD32           programObj
        4           INT32            location
      =>
        1           1                reply
        1                            unused
        2           CARD16           sequence number
        4           m                reply length, m = ((n == 1) ? 0 : n)
        4                            unused
        4           CARD32           n

        if (n = 1) this follows:

        4           FLOAT32          params
        12                           unused

        otherwise this follows:

        16                           unused
        4*n         LISTofFLOAT32    params

    Note that n may be zero, indicating that a GL error occured.

    GetUniformivARB

        1           CARD8            opcode (X assigned)
        1           177              GLX opcode
        2           4                request length
        4           GLX_CONTEXT_TAG  context rag
        4           CARD32           programObj
        4           INT32            location
      =>
        1           1                reply
        1                            unused
        2           CARD16           sequence number
        4           m                reply length, m = ((n == 1) ? 0 : n)
        4                            unused
        4           INT32            n

        if (n = 1) this follows:

        4           INT32            params
        12                           unused

        otherwise this follows:

        16                           unused
        4*n         LISTofINT32      params

    Note that n may be zero, indicating that a GL error occured.

    GetShaderSourceARB

        1           CARD8            opcode (X assigned)
        1           178              GLX opcode
        2           4                request length
        4           GLX_CONTEXT_TAG  context tag
        4           CARD32           obj
        4           CARD32           maxLength
      =>
        1           1                reply
        1                            unused
        2           CARD16           sequence number
        4           m                reply length, m = (n+p)/4
        4                            unused
        4           CARD32           length
        16                           unused
        n           LISTofBYTE       source, n = length+1
        p                            unused, p = pad(n)

    Note that n may be zero, indicating that a GL error occured.

Errors

    The error INVALID_VALUE is generated by any command that takes one or
    more handles as input, and one or more of these handles are not an
    object handle generated by OpenGL. Note that this error is also set when
    passing in the value 0 as a handle, except for UseProgramObjectARB and
    DeleteObject. Passing in 0 to UseProgramObjectARB is valid, and ignored
    by DeleteObject.

    The error INVALID_OPERATION is generated by AttachObjectARB if <obj> is
    not of type SHADER_OBJECT_ARB or if <containerObj> is not of type
    PROGRAM_OBJECT_ARB.

    The error INVALID_OPERATION is generated by AttachObjectARB if <obj> is
    already attached to <containerObj>.

    The error INVALID_OPERATION is generated by DetachObjectARB if
    <attachedObj> is not attached to <containerObj>.

    The error INVALID_OPERATION is generated by DetachObjectARB if
    <containerObj> is not of type PROGRAM_OBJECT_ARB.

    The error INVALID_OPERATION is generated by ShaderSourceARB and
    CompileShaderARB if <shaderObj> is not of type SHADER_OBJECT_ARB.

    The error INVALID_OPERATION is generated by LinkProgramARB if
    <programObj> is not of type PROGRAM_OBJECT_ARB.

    The error INVALID_OPERATION is generated by UseProgramObjectARB if
    <programObj> is not of type PROGRAM_OBJECT_ARB.

    The error INVALID_OPERATION is generated by UseProgramObjectARB if
    <programObj> could not be made part of the current state.

    The error INVALID_OPERATION is generated by GetUniformLocationARB if
    <programObj> is not of type PROGRAM_OBJECT_ARB or if <programObj> has
    not been linked successfully.

    The error INVALID_OPERATION is generated by GetActiveUniformARB if
    <programObj> is not of type PROGRAM_OBJECT_ARB.

    The error INVALID_VALUE is generated by GetActiveUniformARB if <index>
    is greater than or equal to OBJECT_ACTIVE_UNIFORMS_ARB.

    The error INVALID_OPERATION is generated by the Uniform*ARB commands if
    the size does not match the size of the uniform declared in the shader.

    The error INVALID_OPERATION is generated by the Uniform*ARB commands if
    the type does not match the type of the uniform declared in the shader,
    if the uniform is not of type Boolean.

    The error INVALID_OPERATION is generated by the Uniform*ARB commands if
    <location> is not -1 and <location> does not exist for the program object
    currently in use.

    The error INVALID_OPERATION is generated by the Uniform*ARB commands if
    there is no program object in use.

    The error INVALID_OPERATION is generated if a uniform command other than
    Uniform1i{v}ARB is used to load a sampler value.

    The error INVALID_OPERATION is generated by ValidateProgramARB if
    <programObj> is not of type PROGRAM_OBJECT_ARB.

    The error INVALID_OPERATION is generated by GetObjectParameter{if}vARB
    if <pname> is OBJECT_TYPE_ARB or OBJECT_DELETE_STATUS_ARB or
    OBJECT_INFO_LOG_LENGTH_ARB and <obj> is not of type PROGRAM_OBJECT_ARB
    or SHADER_OBJECT_ARB.

    The error INVALID_OPERATION is generated by GetObjectParameter{if}vARB
    if <pname> is OBJECT_LINK_STATUS_ARB or OBJECT_VALIDATE_STATUS_ARB or
    OBJECT_ATTACHED_OBJECTS_ARB or OBJECT_ACTIVE_UNIFORMS_ARB or
    OBJECT_ACTIVE_UNIFORM_MAX_LENGTH_ARB and <obj> is not of type
    PROGRAM_OBJECT_ARB.

    The error INVALID_OPERATION is generated by GetObjectParameter{if}vARB
    if <pname> is OBJECT_SUBTYPE_ARB or OBJECT_COMPILE_STATUS_ARB or
    OBJECT_SHADER_SOURCE_LENGTH_ARB and <obj> is not of type
    SHADER_OBJECT_ARB.

    The error INVALID_OPERATION is generated by GetAttachedObjectsARB if
    <containerObj> is not of type PROGRAM_OBJECT_ARB.

    The error INVALID_OPERATION is generated by GetInfoLogARB if <obj> is
    not of type SHADER_OBJECT_ARB or PROGRAM_OBJECT_ARB.

    The error INVALID_OPERATION is generated by GetShaderSourceARB if <obj>
    is not of type SHADER_OBJECT_ARB.

    The error INVALID_OPERATION is generated by GetUniform{if}vARB if
    <programObj> is not of type PROGRAM_OBJECT_ARB or if <programObj> has
    not been linked successfully or if <location> is not a valid location
    for <programObj>.

    The error INVALID_OPERATION is generated if Begin, RasterPos, or any
    command that performs an explicit Begin is called if:

      - One or more samplers of different types in the current program
        object access the same texture image unit.
      - More than the maximum allowable texture image units are accessed
        based on the count of active samplers and the rest of the GL state
        (note that LinkProgramARB can normally resolve this, except for the
        case where an ARB_vertex_shader shader is mixed with an
        ARB_fragment_program shader or mixed with fixed-function fragment
        processing).

New State

                                                                  Initial
    Get Value                     Type  Get Command                Value    Description             Sec.    Attribute
    ---------                     ----  -------------------------  -------  -----------             ----    ---------
    PROGRAM_OBJECT_ARB             H     GetHandle                    0     Handle of current       2.14.2        -
                                                                            program object

    Table X. New state introduced.

                                                                     Initial
    Get Value                      Type   Get Command                Value        Description          Sec.  Attribute
    ---------                      -----  -----------------------  -------------  -----------          ----   ---------
    -                                H                           object specific  object handle         2.14.1    -
    -                             0+xchar GetInfoLogARB               ""          Info log for shader   6.1.12    -
                                                                                  objects
    -                             0+xchar GetShaderSourceARB          ""          source for a shader   2.14.1    -
    OBJECT_TYPE_ARB                 Z+    GetObjectParameterivARB   SHADER_OBJECT  Type of object        2.14.1    -
    OBJECT_SUBTYPE_ARB              Z+    GetObjectParameterivARB     -            Sub type of object    2.14.1    -
    OBJECT_DELETE_STATUS_ARB        B     GetObjectParameterivARB   FALSE          Shader deleted        2.14      -
    OBJECT_COMPILE_STATUS_ARB       B     GetObjectParameterivARB   FALSE          Compile succeeded     2.14.1    -
    OBJECT_INFO_LOG_LENGTH_ARB      Z+    GetObjectParameterivARB     0            Length of info log    6.1.12    -
    OBJECT_SHADER_SOURCE_LENGTH_ARB Z+    GetObjectParameterivARB     0            Length of source code 6.1.12    -

    Table X Shader object state.

                                                                     Initial
    Get Value                   Type       Get Command                Value         Description            Sec.    Attribute
    ---------                   -----      -----------------------  -------------   -----------            ----    ---------
    -                           0+xZ+      GetActiveUniformARB          -     Size of active uniform        2.14.3      -
    -                           0+xZ+      GetActiveUniformARB          -     Type of active uniform        2.14.3      -
    -                           0+xcharARB GetActiveUniformARB         ""     Name of active uniform        2.14.3      -
    -                           0+xZ       GetUniformLocationARB        -     Location of active uniform    2.14.3      -
    -                           0+xchar    GetInfoLogARB               ""     Info log for program objects  6.1.12      -
    OBJECT_ATTACHED_OBJECTS_ARB Z+         GetObjectParameterivARB     0      Number of attached objects    6.1.12      -
    OBJECT_ACTIVE_UNIFORMS_ARB  Z+         GetObjectParameterivARB     0      Number of active uniforms     2.14.3      -
    OBJECT_DELETE_STATUS_ARB    B          GetObjectParameterivARB   FALSE          Program object deleted  2.14        -
    OBJECT_LINK_STATUS_ARB      B          GetObjectParameterivARB   FALSE          Link succeeded          2.14.2      -
    OBJECT_VALIDATE_STATUS_ARB  B          GetObjectParameterivARB   FALSE          Validate succeeded      2.15        -
    OBJECT_INFO_LOG_LENGTH_ARB  Z+         GetObjectParameterivARB     0            Length of info log      6.1.12      -
    OBJECT_TYPE_ARB             Z+         GetObjectParameterivARB   PROGRAM_OBJECT Type of object          2.14.2      -
    OBJECT_ACTIVE_UNIFORM_
                MAX_LENGTH_ARB  Z+         GetObjectParameterivARB     0            Max uniform name length 6.1.12      -
    -                           0+xhandle  GetAttachedObjectsARB     empty list     Shader objects attached 6.1.12
    -                           H                                  object specific  object handle           2.14.2      -

    Table X Program object state.

New Implementation Dependent State

        None

Sample Usage

    For examples on how to use GetUniformLocationARB and the Uniform*ARB
    API, see issue 32.

    //
    // Example usage of GetActiveUniformARB.
    //
    GLint maxLength;
    GLint i, uniformCount;
    GLcharARB **name;
    GLsizei *length;
    GLint *size;
    GLenum *type;

    //
    // Get the number of uniforms, and the length of the longest name.
    //
    glGetObjectParameterivARB(programObject,
                              GL_OBJECTS_ACTIVE_UNIFORM_MAX_LENGTH_ARB,
                              &maxLength);
    glGetObjectParameterivARB(programObject, GL_OBJECTS_ACTIVE_UNIFORMS_ARB,
                              &uniformCount);

    //
    // Allocate arrays to store the answers in. For simplicity, the return
    // from malloc is not checked for NULL.
    //
    size   = (GLint *) malloc(uniformCount * sizeof(GLint));
    type   = (GLint *) malloc(uniformCount * sizeof(GLenum));
    length = (GLsizei *) malloc(uniformCount * sizeof(GLsizei));
    name   = (GLcharARB **) malloc(uniformCount * sizeof(GLcharARB **));

    //
    // Loop over glGetActiveUniformARB and store the results away.
    //
    for (i = 0; i < uniformCount; i++) {
        name[i] = (GLcharARB *) malloc(maxLength * sizeof(GLcharARB));
        glGetActiveUniformARB(programObject, i, maxLength, &length[i],
                              &size[i], &type[i], name[i]);
    }

    See the ARB_vertex_shader and ARB_fragment_shader extension documents
    for more examples.

Revision History

    Revision: 0.5 6/5/2002
      - First draft for circulation
    Revision: 0.51
      - Started issues section. Added string discussions and uniform
        discussions.
      - Added content to the Contributors, and Errors section
      - Named and explained all parameters to all API calls
      - Added a new GLchar type
      - Load/AppendShaderGL2 take a length argument
      - GetUniformLocationGL2 takes a length argument for the string passed
        in
      - GetInfoLogGL2 now also optionally returns the length of the string
      - Clarified DetachObjectGL2 and DeleteObject(s)GL2 and their
        interaction
    Revision 0.52
      - Removed NULL_HANDLE_GL2
      - Added explanation of what happens when program and shader objects
        are shared among contexts.
    Revision: 0.60
      - Merged GL2_core_objects extension into this one. Core_objects is now
        obsolete.
    Revision: 0.61
      - Took out any reference to 'project'. This term was unnecessary,
        since it meant the same as program object.
    Revision: 0.62
      - Now references V1.0 of OpenGL Shading Language Specification
      - Fixed minor typos
      - Accepted by the GL2 working group
    Revision: 0.63 10/17/2002
      - Removed IsObjectGL2(). It overlaps with GetObjectParameter{if}vGL2.
      - Expanded GetObjectParameter{if}GL2. Added OBJECT_TYPE_GL2.
    Revision: 0.64 10/18/2002
      - Added list of entrypoints that are not compiled into a display list
        to section 5.
      - Updated Errors section.
    Revision: 0.65 10/23/2002
      - Added GetShaderSourceGL2.
      - Added GetUniform{if}vGL2
      - Updated errors section.
      - Moved shader resources section in here from GL2_vertex_shader.
    Revision: 0.7 10/29/2002
      - Added issue number 16.
      - Second distribution to the GL2 working group.
      - Now written against the OpenGL 1.4 specification.
    Revision: 0.71 11/26/2002
      - Added six more issues discussion uniform loading (issues 7-15).
      - Added loadUniform commands to load values for INT and BOOL declared
        uniforms.
      - Changed the behavior for loadUniforms to allow to load the first N
        values if loading into a uniform declared with an extent bigger than
        N.
      - Made a GLhandle an unsigned integer, read and written only by the GL
      - Added high level shading language layering issue 22. This issue came
        from the OpenGL Shading Language document.
      - Updated resource limits issue number 21.
    Revision: 0.72 01/27/2003
      - Added issue 24.
      - Added to the list of contributors.
      - Changed the GLchar type to GLcharGL2
      - Changed GLhandle type to GLhandleGL2
    Revision: 0.73 02/20/2003
      - Updated section 2.14.4. Loading uniforms of the wrong type will
        result in undefined shader results.
      - Loading more or less data than the declared extent of the uniform is
        now handled consistently.
      - Added section 2.14.4.1 'Samplers'
      - Added an extra error condition for LinkProgramGL2 when using too
        many active samplers.
      - Added issue 25, explaining how to use samplers for texture access.
      - Added issue 26, need for a validate command.
      - Added section 2.15, Validation
    Revision: 0.74 02/23/2003
      - Added use of [] and . (dot) operators in GetUniformLocationGL2
      - Refined wording in section 2.14.4.1.
    Revision: 0.75 03/27/2003
      - Begin can generate an error in certain cases.
      - Closed issue 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 and made spec
        changes, if necessary, to reflect the resolutions of these issues.
      - Added issues 27, 28, 29, 30, 31.
      - Changed the loadUniform API. Less entry points, aimed at performance
        of loading uniforms. Also added a transpose flag to the matrix ones.
      - Updated IP Status section to point to the contributors agreement.
      - Removed ObjectParameter*GL2. These are not used anywhere.
      - AttachObjectGL2 no longer returns a Boolean. There is no reason that
        an attach should ever fail, if a valid program object and shader
        object are passed in.
      - Defined the lifetime of the pointers returned by GetInfoLogGL2 and
        GetShaderSourceGL2.
      - Added GetAttachedObjectsGL2.
    Revision: 0.76 03/28/2003
      - UseProgramObjectGL2 no longer returns anything. It can now be
        compiled into a display list.
      - Closed issues 14, 15, 30.
      - Allowed loading more than one element in a uniform array, by just
        querying the location of the first element to be loaded.
      - Added the UNIFORM_ERROR_CHECK_GL2 enable.
      - Changed GetInfoLogGL2 so that GL only has to maintain at least one
        info log for shader objects and at least one for program objects.
      - Added section 2.16, undefined behavior
    Revision: 0.77 04/03/2003
      - AppendShader now takes an array of strings, just like ShaderSource.
      - GetShaderSources returns an array of strings.
      - Closed issues 16, 17, 18, 19, 20.
    Revision: 0.78 04/07/2003
      - Closed issues 21, 22, 23, 24, 25, 26.
      - Added lifetime to the pointer returned by ValidateProgram. Also
        changed ValidateProgram to take a handle to a program object.
      - LinkProgramGL2 will now set all uniforms to zero.
      - Added GetShaderSourceGL2 example code.
    Revision: 0.79 04/09/2003
      - Added section 2.17, required state.
      - Clarified GetInfoLog, especially when sharing objects across
        contexts.
      - Changed ValidateProgramGL2 to store its information in the info log.
        It'll return a Boolean to indicate a successful validation.
      - Clarified the use of the '.' And '[]' operators in
        GetUniformLocation.
    Revision: 0.80 04/17/2003
      - Removed AppendShaderGL2.
      - Closed issues 28, 29, 30 and 31.
      - Clarified GetUniformLocationGL2 based on Folker's feedback.
      - Added GetActiveUniformsGL2.
    Revision: 0.81 04/18/2003
      - GetUniformLocationGL2 only works for active uniforms now.
      - Re-worded GetActiveUniformsGL2 to be more like GetActiveAttribsGL2.
      - Added wording explicitly saying that a failed compile or link is not
        state neutral (does not revert back to the old state).
      - Added a sentence saying that the memory pointer returned by
        GetActiveUniforms, GetInfoLog, GetAttachedObjects and
        GetShaderSource is owned by OpenGL and should not be overwritten by
        the caller.
    Revision: 0.82 04/27/2003
      - Forgot to close issue 27.
      - Changed a few occurances of "char" to charGL2.
      - Updated language describing GetUniformLocationGL2.
      - Changed the location of the Contributors License to a publicly
        accessible place on www.3dlabs.com.
      - GetActiveUniformsGL2 is not display-listable.
      - Removed one error condition for ValidateProgramGL2.
      - Added errors for GetAttachedObjectsGL2.
      - Renamed the following functions:
      - glLoadShader --> glShaderSource
      - glGetShaderString --> glGetShaderSource
      - glAttachShaderObject --> glAttachObject
      - glGetAttachedShaderObjects --> glGetAttachedObjects
      - Clarified that GetActiveUniformsGL2 will return as much information
        as possible. If it has none, it'll return a count of zero.
      - Numerous clarifications and some reordering of paragraphs based on
        Pat's feedback.
      - Spelled out three reasons why LinkProgram can fail.
      - Spelled out that the Uniform*GL2 command used needs to match both
        the type and the size of a uniform declared in a shader.
      - Updated the error checking rules for the Uniform*GL2 commands.
      - Passing in '0', or a handle that is not an object handle generated
        by the GL, results in the error INVALID_VALUE. All other calls that
        get passed a valid handle, but that handle is of the wrong type for
        that operation, set an INVALID_OPERATION error.
      - Added issue 32, explaining GetUniformLocationGL2 and uniform
        loading.
    Revision: 0.83 04/28/2003
      - Added more state tables.
      - Added Kent Lin to the list of contributors.
    Revision: 0.84 04/29/2003
      - Added a few more examples to issue 32.
      - Clarified the Errors section with respect to passing in 0 as a
        handle.
      - Version voted on, and approved, by the ARB-GL2 working group.
    Revision: 0.85 05/09/2003
      - Fixed a mistake in the program object state table for GetInfoLogGL2.
      - Fixed a mistake in the resolution of issue 27.
      - Clarified the resolution of issue 17.
      - Clarified that in case of doubt by the compiler/linker, a uniform
        will be marked as active. Section 2.14.3 (intro).
      - Clarified that you need to pass in three NULL pointers to
        GetActiveUniformsGL2, to only get the count of active uniforms.
      - Clarified the lifetime of the pointers returned by
        GetActiveUniformsGL2, GetShaderSourceGL2 and GetAttachedObjectsGL2.
      - Fixed a typo in the first entry in the Errors section.
      - Changed the count parameter in the Uniform*vGL2 commands to be of
        type sizei. Also did this for ShaderSourceGL2.
      - Expanded the two paragraphs explaining how Uniform*GL2 works into
        several smaller ones.
      - Clarified that GetInfoLogGL2 returns NULL if the handle passed in is
        invalid, or not a program or shader object.
      - Added fourth implicit error rule to section 2.5, GL Errors. Note
        that this rule was already in the Errors section.
      - Added Jon Leech, Evan Hart, Benjamin Lipchak and Jeremy Sandmel to
        the list of contributors.
      - Assigned enum values.
    Revision: 0.86 05/15/2003
      - Assigned missing enum value to SHADER_OBJECT_GL2.
      - Replaced all GL2 occurrences with ARB. Fixed some typos.
      - Added several more to the contributors list. If anyone is still left
        out, let Bill Licea Kane, Jon Leech or myself know.
    Revision: 0.87 06/13/2003
      - Changed resolution of issue 27 and the description of GetInfoLog to
        have an info log per object. Removed the info log language from the
        AGL/GLX/WGL section.
      - Changed the resolution of issue 14, 15, 25 (uniform API name).
      - Changed the discussion and resolution of issue 30. (uniform
        loading).
      - Added issue 33.
      - Changed the uniform API commands. The type of the uniform is no
        longer encoded in the name of the API.
      - Updated section 2.14.4, samplers.
      - Updated the Errors section w.r.t. uniform loading
      - Updated section 2.16, undefined behavior.
      - Deleted DeleteObjectsARB.
      - Removed the Boolean return from CompileShaderARB, LinkProgramARB and
        ValidateProgramARB.
      - Added several new error conditions for GetObjectParameter{if}vARB to
        the Errors section an section 6.1.12.
      - Updated the New State and Required State sections.
      - Changed GetInfoLog to no longer return a pointer to GL memory.
      - Changed GetAttachedObjects to no longer return a pointer to GL
        memory.
      - Changed GetActiveUniform to no longer return a pointer to GL memory.
        This call now returns data for one active uniform, instead of all
        active uniforms. Also added its returns (type, size and name) to the
        state tables and Required State section.
      - Changed GetShaderSource to no longer return a pointer to GL memory.
      - Added OBJECT_SUBTYPE_ARB, OBJECT_DELETE_STATUS_ARB,
        OBJECT_COMPILE_STATUS_ARB, OBJECT_LINK_STATUS_ARB,
        OBJECT_VALIDATE_STATUS_ARB, OBJECT_INFO_LOG_LENGTH_ARB,
        OBJECT_ATTACHED_OBJECTS_ARB, OBJECT_ACTIVE_UNIFORMS_ARB,
        OBJECT_ACTIVE_UNIFORM_MAX_LENGTH_ARB,
        OBJECT_SHADER_SOURCE_LENGTH_ARB as a queriable parameter to
        GetObjectParameter{if}vARB.
      - Modified the introduction to section 2.14 to mention texture and
        display list objects.
      - Added issue 34.
      - Updated the example section with a new example.
      - Re-ordered the Errors section. They are now in the order of API
        calls described in Sections 2-6.
      - Language clean-up throughout the document.
      - Consistently used "OpenGL Shading Language" where appropriate (This
        is the official name).
      - Changed issue 5. This issue is now obsolete, with the new GetInfoLog
        API.
      - Clarified section 2.14.4, Samplers. The values to load range from 0
        to to max available texture image units.
      - ARB approved version.
    Revision: 0.88 03/29/2004
      - Added ARB extension number (31) and edited the status paragraph.
      - GetActiveUniform now returns types for samplers.
      - If at least one element in a uniform array is active, then this
        array will be reported by GetActiveUniform as being active starting
        at element 0 through the highest element used. Added issue 35
        explaining this in detail.
      - Passing in a location of -1 to Uniform*ARB will be silently ignored
        (no GL error will be generated). Also added issue 36 explaining
        this.
      - DeleteObject will silently ignore the value 0. Added issue 37.
      - The current program object handle is no longer part of the 'current'
        state.
      - Specified that GetUniform returns values in column major order for
        matrices. Also clarified that GetUniform returns only one element of
        an array of uniforms. Added issue 38.
      - Specified what happens when ValidateProgramARB fails. This means
        that the program object will not execute, and no fragments will be
        rendered.
      - Added 'const' to the data passed in the Uniform*vARB commands.
      - Clarified that return parameters of the various Get commands are
        unmodified if an error occurred.
      - Added issue 39.
      - Added issue 40, and clarified failed re-link behavior in the spec.
      - Added issue 41.
      - Clarified that the compile status of a shader object does not change
        when source is loaded in it.
      - Clarified that the link status of a program object is not affected
        by attaching or detaching or re-compiling attached shader objects.
      - Few fixes to the Errors section.
      - Clarified GetUniformLocation and GetActiveUniform when addressing
        the first element of an array. Added issue 42 explaining this.
      - Added issue 43, 44 and 45.
    Revision: 0.89 04/06/2004
      - Updated the Shading Language Version referenced to the now official
        version 1.10.
      - Added language describing the Uniform* loading commands that
        Uniform1i{v} is used to load samplers.
      - Clarified issues 36, 42 and 43 based on Pat's feedback.
      - Changed the examples in issue 45 a bit. Hopefully for the better.
      - Added issue 46.
      - Removed an error condition I had added earlier for glBegin().
      - Expanded section 2.15 to include the exact conditions when
        validation is allowed to fail. Previously these conditions were only
        in the Errors section, listed for glBegin().
      - ARB-GL2 workgroup approved version.
    Revision: 0.90 12/14/2009
      - Added GLX protocol