Name

    NV_command_list

Name Strings

    GL_NV_command_list

Contact

    Pierre Boudier, NVIDIA (pboudier 'at' nvidia.com)
    Christoph Kubisch, NVIDIA (ckubisch 'at' nvidia.com)
    Tristan Lorach, NVIDIA (tlorach 'at' nvidia.com)

Contributors

    Jeff Bolz, NVIDIA
    Corentin Wallez, NVIDIA
    Markus Tavenrath, NVIDIA
    Mark Kilgard, NVIDIA
    Joseph Emmons, NVIDIA
    Thomas Ludwig, MAXON

Status

    Shipping with NVIDIA driver release 347.88 (March 2015)

Version

    Last Modified Date: November 3, 2015
    Revision: 6

Number

    OpenGL Extension #477

Dependencies

    This extension interacts with NV_vertex_buffer_unified_memory.
    
    This extension interacts with NV_uniform_buffer_unified_memory.
    
    This extension interacts with NV_parameter_buffer_object.
    
    This extension interacts with ARB_robust_buffer_access_behavior
    
    This extension interacts with NV_bindless_texture and ARB_bindless_texture
    
    This extension interacts with NV_shader_buffer_load
    
    This extension interacts with ARB_shader_draw_parameters
    
    The extension is written against the OpenGL 4.4 Specification, 
    Compatibility Profile.

Overview

    This extension adds a few new features designed to provide very low 
    overhead batching and replay of rendering commands and state changes:

    - A state object, which stores a pre-validated representation of the
      the state of (almost) the entire pipeline.

    - A more flexible and extensible MultiDrawIndirect (MDI) type of mechanism, using
      a token-based command stream, allowing to setup binding state and emit draw calls.

    - A set of functions to execute a list of the token-based command streams with state object
      changes interleaved with the streams.

    - Command lists enabling compilation and reuse of sequences of command
      streams and state object changes.

    Because state objects reflect the state of the entire pipeline, it is 
    expected that they can be pre-validated and executed efficiently. It is 
    also expected that when state objects are combined into a command list,
    the command list can diff consecutive state objects to produce a reduced/
    optimized set of state changes specific to that transition.

    The token-based command stream can also be stored in regular buffer objects
    and therefore be modified by the server itself. This allows more 
    complex work creation than the original MDI approach, which was limited
    to emitting draw calls only.

New Procedures and Functions

    void CreateStatesNV(sizei n, uint *states);
    void DeleteStatesNV(sizei n, const uint *states);
    boolean IsStateNV(uint state);

    void StateCaptureNV(uint state, enum mode);

    uint   GetCommandHeaderNV(enum tokenID, uint size);
    ushort GetStageIndexNV(enum shadertype);
    
    void DrawCommandsNV(enum primitiveMode, uint buffer, const intptr* indirects, const sizei* sizes, 
                        uint count);
    void DrawCommandsAddressNV(enum primitiveMode, const uint64* indirects, const sizei* sizes, 
                               uint count);

    void DrawCommandsStatesNV(uint buffer, const intptr* indirects, const sizei* sizes, 
                                   const uint* states, const uint* fbos, uint count);
    void DrawCommandsStatesAddressNV(const uint64* indirects, const sizei* sizes, 
                                     const uint* states, const uint* fbos, uint count);

    void CreateCommandListsNV(sizei n, uint *lists);
    void DeleteCommandListsNV(sizei n, const uint *lists);
    boolean IsCommandListNV(uint list);
    
    void ListDrawCommandsStatesClientNV(uint list, uint segment, const void** indirects, 
                                        const sizei* sizes, const uint* states, const uint* fbos, uint count);
    
    void CommandListSegmentsNV(uint list, uint segments);
    void CompileCommandListNV(uint list);
    void CallCommandListNV(uint list);
  
New Tokens

    Used in DrawCommandsStates buffer formats, in
    GetCommandHeaderNV to return the header:


      TERMINATE_SEQUENCE_COMMAND_NV                      0x0000
      NOP_COMMAND_NV                                     0x0001
      DRAW_ELEMENTS_COMMAND_NV                           0x0002
      DRAW_ARRAYS_COMMAND_NV                             0x0003
      DRAW_ELEMENTS_STRIP_COMMAND_NV                     0x0004
      DRAW_ARRAYS_STRIP_COMMAND_NV                       0x0005
      DRAW_ELEMENTS_INSTANCED_COMMAND_NV                 0x0006
      DRAW_ARRAYS_INSTANCED_COMMAND_NV                   0x0007
      ELEMENT_ADDRESS_COMMAND_NV                         0x0008
      ATTRIBUTE_ADDRESS_COMMAND_NV                       0x0009
      UNIFORM_ADDRESS_COMMAND_NV                         0x000a
      BLEND_COLOR_COMMAND_NV                             0x000b
      STENCIL_REF_COMMAND_NV                             0x000c
      LINE_WIDTH_COMMAND_NV                              0x000d
      POLYGON_OFFSET_COMMAND_NV                          0x000e
      ALPHA_REF_COMMAND_NV                               0x000f
      VIEWPORT_COMMAND_NV                                0x0010
      SCISSOR_COMMAND_NV                                 0x0011
      FRONT_FACE_COMMAND_NV                              0x0012
          

Additions to Chapter 5 of the OpenGL 4.4 (Compatibility) Specification
(Shared Objects and Multiple Contexts)

    Add state objects and command lists to the set of objects that can not be 
    shared between contexts.
    
Additions to Chapter 7 of the OpenGL 4.4 (Compatibility) Specification
(Shared Objects and Multiple Contexts)

    Modify Section 7.12.2, Shader Memory Access Synchronization
    
    (modify list of barrier bits)
    
    * COMMAND_BARRIER_BIT: Command data sourced from buffer objects by
      Draw*Indirect, DispatchComputeIndirect and DrawCommands*NV commands 
      after the barrier will reflect data written by shaders prior to the 
      barrier. The buffer objects affected by this bit are derived from the
      DRAW_INDIRECT_BUFFER and DISPATCH_INDIRECT_BUFFER bindings, or 
      from the arguments passed to DrawCommands*NV.

Additions to Chapter 10 of the OpenGL 4.4 (Compatibility) Specification 
(Drawing Commands)

Add a new Section 10.X (Indirect Draw Commands With State Changes)

Add a new subsection 10.X.1 (State Objects)

    The current state of the rendering pipeline can be captured into a state 
    object for later reuse with a new set of drawing commands. The name space
    for state objects is the unsigned integers, with zero reserved. The 
    command:

        void CreateStatesNV(sizei n, uint *states);

    returns <n> previously unused state object names in <states>, and creates
    a state object in the initial state for each name.

    State objects are deleted by calling

        void DeleteStatesNV(sizei n, const uint *states);

    <states> contains <n> names of state objects to be deleted. Once a state
    object is deleted it has no contents and its name is again unused. Unused 
    names in <states> are silently ignored, as is the value zero.

    All the states that can be set via DrawCommandsStatesNV (as defined in 
    Section 10.X.2) are excluded from the captured state and will be inherited 
    from the most recent commands or GL context state. Binding state is, however,
    never inherited from GL context, only from commands.

    
    The command 
    
        void StateCaptureNV(uint state, enum basicmode);

    captures the current state of the rendering pipeline into the object 
    indicated by <state>. <basicmode> indicates the basic Begin mode that this
    state object must be used with, see Table 10.X.1.2 for compatibility
    between primitive modes and basic modes.
  
        Table 10.X.1.2 (Primitive mode compatibility)

        basic primitive mode        | compatible primitive mode
        ---------------------------------------------------------------------
        POINTS                      | POINTS
        LINES                       | LINES
                                    | LINE_STRIP
                                    | LINE_LOOP
        TRIANGLES                   | TRIANGLES
                                    | TRIANGLE_STRIP
                                    | TRIANGLE_FAN
        QUADS                       | QUADS
                                    | QUAD_STRIP
        PATCHES                     | PATCHES
        LINES_ADJACENCY             | LINES_ADJACENCY
                                    | LINES_STRIP_ADJACENCY
        TRIANGLES_ADJACENCY         | TRIANGLES_ADJACENCY
                                    | TRIANGLES_STRIP_ADJACENCY

    This rendering state includes:

    - Vertex attribute enable state, formats, types, relative offsets and strides.
      
    - Primitive state such as primitive restart and patch parameters, provoking vertex.
      
    - Immediate vertex attribute values as provided by glVertexAttrib* or
      glVertexAttribI*
      
    - All active program binaries except compute (either from the active 
      program pipeline or from UseProgram) with their current subroutine 
      configuration.
    
    - Rasterization, multisample fragment operation, depth, stencil, and 
      blending state.
      
    - Rasterization state such as stippling and polygon modes and offsets.

    - Viewport, scissor, and depth range state.

    - Framebuffer attachment configuration: attachment state including attachment 
      formats, drawbuffer state, and target/layer information, but not including 
      actual attachments or sizes of attachments (these are stored separately).
     
    - Framebuffer attachment textures (but not their residency state).
    
    It does NOT include:

    - Bound vertex buffers or vertex unified addresses, or their offsets,
      or bound index buffers/addresses.

    - Other program-related bindings, such as shader storage buffers, atomic counter buffers, texture
      and sampler bindings.

    - Default-block uniform values from active programs

    - Blending constant color, front and back stencil reference values, alpha test threshold.

    - Polygon offset values.

    - Viewport and scissor rectangle for viewport index zero.

    Essentially all state that can be manupulated by the commands listed in 10.X.2 (Drawing with Commands)
    is excluded from the state capture.
     
    INVALID_ENUM is generated if <mode> is not a basic primitive mode, as listed
    in Table 10.X.1.2.
    INVALID_OPERATION is generated if the default framebuffer is bound as either draw or read buffer.
    INVALID_OPERATION is generated if transform feedback is enabled.
    INVALID_OPERATION is generated if occlusion query is enabled.
    INVALID_OPERATION is generated if the current active program or program pipeline
    makes use of SHADER_STORAGE_BUFFER, ATOMIC_COUNTER_BUFFER or has uniforms defined
    in the default uniform-block, or uniforms inheriting from fixed function state 
    (gl_ModelView etc.).
    INVALID_OPERATION is generated if the current active program or program pipeline
    uses uniform blocks that did not have the "commandBindableNV" flag set (see
    "Modifications to the OpenGL Shading Language Specification" section).
    INVALID_OPERATION is generated if neither program, nor program pipeline
    objects are actively used.

Add a new subsection 10.X.2 (Drawing with Commands)
    
        void DrawCommandsNV(enum mode, uint buffer, const intptr* indirects, const sizei* sizes, 
                            uint count);
        void DrawCommandsAddressNV(enum mode, const uint64* indirects, const sizei* sizes, 
                                   uint count);

    These commands accept arrays of buffer addresses (either an array of 
    offsets <indirects> into a buffer named by <buffer>, or an array of GPU 
    addresses <indirects>), and an array of sequence lengths in <sizes>. 
    All arrays have <count> entries.
    The current binding state of vertex, element and uniform buffers will not be
    effective but must be set via commands within the buffer, other state will
    however be inherited from the current OpenGL context.

    INVALID_ENUM is generated if <mode> is not an accepted value.
    INVALID_VALUE is generated if <buffer> is not a valid buffer object.
    INVALID_OPERATION is generated if a geometry shader is active and <mode> is 
    incompatible with the input primitive type of the geometry shader in the currently
    installed program object.
    INVALID_OPERATION is generated if the default (zero) frame buffer object is
    currently bound as DRAW_FRAMEBUFFER, a non-zero frame buffer object is required.
    
    DrawCommandsNV and DrawCommandsAddressNV are equivalent to:

        Save current GL state;
        enum indexType = UNSIGNED_SHORT;
        for (uint i = 0; i < count; i++) {
            uint64 address = address computed from <buffer>+<indirects>[i];
            
            indexType = DrawCommandSequenceNV(<mode>, indexType, address, sizes[i]);
        }
        Restore current GL state;
        
    The command:

        enum DrawCommandSequenceNV(enum mode, enum indexType, void *address, sizei size);

    does not exist in the GL, but is used to describe functionality in the rest
    of this section. 
    
    DrawCommandSequenceNV is a flexible and extensible command that executes
    simple state changes and draw commands based on a tokenized format. The
    loop above illustrates that the state changes from one invocation will
    influence the next. All rendering is peformed as if the client states for
    VERTEX_ATTRIB_ARRAY_UNIFIED_NV, ELEMENT_ARRAY_UNIFIED_NV and 
    UNIFORM_BUFFER_UNIFIED_NV are enabled.
    
    It is defined by the following pseudo code, tokens, and structures:


    Table 10.X.2 (Token values and command structure names)

      tokenID                               | Command
      ---------------------------------------------------------------------
        TERMINATE_SEQUENCE_COMMAND_NV       | TerminateSequenceCommandNV
        NOP_COMMAND_NV                      | NOPCommandNV
        DRAW_ELEMENTS_COMMAND_NV            | DrawElementsCommandNV
        DRAW_ARRAYS_COMMAND_NV              | DrawArraysCommandNV
        DRAW_ELEMENTS_STRIP_COMMAND_NV      | DrawElementsCommandNV
        DRAW_ARRAYS__STRIP_COMMAND_NV       | DrawArraysCommandNV
        DRAW_ELEMENTS_INSTANCED_COMMAND_NV  | DrawElementsInstancedCommandNV
        DRAW_ARRAYS_INSTANCED_COMMAND_NV    | DrawArraysInstancedCommandNV
        ELEMENT_ADDRESS_COMMAND_NV          | ElementAddressCommandNV
        ATTRIBUTE_ADDRESS_COMMAND_NV        | AttributeAddressCommandNV
        UNIFORM_ADDRESS_COMMAND_NV          | UniformAddressCommandNV
        BLEND_COLOR_COMMAND_NV              | BlendColorCommandNV
        STENCIL_REF_COMMAND_NV              | StencilRefCommandNV
        LINE_WIDTH_COMMAND_NV               | LineWidthCommandNV
        POLYGON_OFFSET_COMMAND_NV           | PolygonOffsetCommandNV
        ALPHA_REF_COMMAND_NV                | AlphaRefCommandNV
        VIEWPORT_COMMAND_NV                 | ViewportCommandNV
        SCISSOR_COMMAND_NV                  | ScissorCommandNV
        FRONT_FACE_COMMAND_NV               | FrontFaceCommandNV


        Tight packing is used for all structures
        
        typedef struct {
          uint  header;
        } TerminateSequenceCommandNV;

        typedef struct {
          uint  header;
        } NOPCommandNV;
        
        typedef  struct {
          uint  header;
          uint  count;
          uint  firstIndex;
          uint  baseVertex;
        } DrawElementsCommandNV;

        typedef  struct {
          uint  header;
          uint  count;
          uint  first;
        } DrawArraysCommandNV;
        
        typedef  struct {
          uint  header;
          uint  mode;
          uint  count;
          uint  instanceCount;
          uint  firstIndex;
          uint  baseVertex;
          uint  baseInstance;
        } DrawElementsInstancedCommandNV;

        typedef  struct {
          uint  header;
          uint  mode;
          uint  count;
          uint  instanceCount;
          uint  first;
          uint  baseInstance;
        } DrawArraysInstancedCommandNV;

        typedef struct {
          uint  header;
          uint  addressLo;
          uint  addressHi;
          uint  typeSizeInByte;
        } ElementAddressCommandNV;

        typedef struct {
          uint  header;
          uint  index;
          uint  addressLo;
          uint  addressHi;
        } AttributeAddressCommandNV;

        typedef struct {
          uint    header;
          ushort  index;
          ushort  stage;
          uint    addressLo;
          uint    addressHi;
        } UniformAddressCommandNV;

        typedef struct {
          uint  header;
          float red;
          float green;
          float blue;
          float alpha;
        } BlendColorCommandNV;

        typedef struct {
          uint  header;
          uint  frontStencilRef;
          uint  backStencilRef;
        } StencilRefCommandNV;
        
        typedef struct {
          uint  header;
          float lineWidth;
        } LineWidthCommandNV;

        typedef struct {
          uint  header;
          float scale;
          float bias;
        } PolygonOffsetCommandNV;
        
        typedef struct {
          uint  header;
          float alphaRef;
        } AlphaRefCommandNV;

        typedef struct {
          uint  header;
          uint  x;
          uint  y;
          uint  width;
          uint  height;
        } ViewportCommandNV; // only ViewportIndex 0

        typedef struct {
          uint  header;
          uint  x;
          uint  y;
          uint  width;
          uint  height;
        } ScissorCommandNV; // only ViewportIndex 0

        typedef struct {
          uint  header;
          uint  frontFace; // 0 for CW, 1 for CCW
        } FrontFaceCommandNV;

        enum DrawCommandSequenceNV(enum mode, enum indexType, void *address, sizei size)
        {
          enum modeStrip;
          if      (mode == TRIANGLES)            modeStrip = TRIANGLE_STRIP;
          else if (mode == LINES)                modeStrip = LINE_STRIP;
          else if (mode == LINES_ADJACENCY)      modeStrip = LINE_STRIP_ADJACENCY;
          else if (mode == TRIANGLES_ADJACENCY)  modeStrip = TRIANGLE_STRIP_ADJACENCY;
          else if (mode == QUADS)                modeStrip = QUAD_STRIP;
          else    modeStrip = mode;

          enum modeSpecial;
          if      (mode == LINES)      modeSpecial = LINE_LOOP;
          else if (mode == TRIANGLES)  modeSpecial = TRIANGLE_FAN;
          else    modeSpecial = mode;

          void *current = address;
          
          while (current != (ubyte *)address + size) {
            uint    header  = *(uint*)current;

            switch( GetTokenType(header)){
            case TERMINATE_SEQUENCE_NV:
              {
                return indexType;
              }
              break;
            case NOP_COMMAND_NV:
            
              break;
            case DRAW_ELEMENTS_COMMAND_NV:
              {
                DrawElementsCommandNV* cmd = (DrawElementsCommandNV*)current;
                DrawElementsBaseVertex(mode, cmd->count, indexType, (void*)(cmd->firstIndex * sizeofindextype), cmd->baseVertex);
              }
              break;
            case DRAW_ARRAYS_COMMAND_NV:
              {
                DrawArraysCommandNV* cmd = (DrawArraysCommandNV*)current;
                DrawArrays(mode, cmd->first, cmd->count);
              }
              break;
            case DRAW_ELEMENTS_STRIP_COMMAND_NV:
              {
                DrawElementsCommandNV* cmd = (DrawElementsCommandNV*)current;
                DrawElementsBaseVertex(modeStrip, cmd->count, indexType, (void*)(cmd->firstIndex * sizeofindextype), cmd->baseVertex);
              }
              break;
            case DRAW_ARRAYS_STRIP_COMMAND_NV:
              {
                DrawArraysCommandNV* cmd = (DrawArraysCommandNV*)current;
                DrawArrays(modeStrip, cmd->first, cmd->count);
              }
              break;
            case DRAW_ELEMENTS_INSTANCED_COMMAND_NV:
              {
                // undefined behavior if (cmd->mode != mode && cmd->mode != modeStrip && cmd->mode != modeSpecial)
                
                DrawElementsInstancedCommandNV* cmd = (DrawElementsInstancedCommandNV*)current;
                DrawElementsIndirect(cmd->mode, indexType, &cmd->count);
              }
              break;
            case DRAW_ARRAYS_INSTANCED_COMMAND_NV:
              {
                // undefined behavior if (cmd->mode != mode && cmd->mode != modeStrip && cmd->mode != modeSpecial)
                
                DrawArraysInstancedCommandNV* cmd = (DrawArraysInstancedCommandNV*)current;
                DrawArraysIndirect(cmd->mode, &cmd->count);
              }
              break;
            case ELEMENT_ADDRESS_COMMAND_NV:
              {
                ElementAddressCommandNV* cmd = (ElementAddressCommandNV*)current;
                switch(cmd->typeSizeInByte){
                  case 1: indexType = UNSIGNED_BYTE;  break;
                  case 2: indexType = UNSIGNED_SHORT; break;
                  case 4: indexType = UNSIGNED_INT;   break;
                }
                BufferAddressRangeNV(ELEMENT_ARRAY_ADDRESS_NV, 0, uint64(cmd->addressLo) | (uint64(cmd->addressHi)<<32), 0x7FFFFFFF);
              }
              break;
            case ATTRIBUTE_ADDRESS_COMMAND_NV:
              {
                AttributeAddressCommandNV* cmd = (AttributeAddressCommandNV*)current;
                BufferAddressRangeNV(VERTEX_ATTRIB_ARRAY_ADDRESS_NV, cmd->index, uint64(cmd->addressLo) | (uint64(cmd->addressHi)<<32), 0x7FFFFFFF);
              }
              break;
            case UNIFORM_ADDRESS_COMMAND_NV:
              {
                UniformAddressCommandNV* cmd = (UniformAddressCommandNV*)current;
                BufferAddressRangeNV(UNIFORM_BUFFER_ADDRESS_NV, cmd->index, uint64(cmd->addressLo) | (uint64(cmd->addressHi)<<32), 0x10000);
              }
              break;
            case BLEND_COLOR_COMMAND_NV:
              {
                BlendColorCommandNV* cmd = (BlendColorCommandNV*)current;
                BlendColor(cmd->red,cmd->green,cmd->blue,cmd->alpha);
              }
              break;
            case STENCIL_REF_COMMAND_NV:
              {
                StencilRefCommandNV* cmd = (StencilRefCommandNV*)current;
                StencilFuncSeparate(FRONT, asIs, cmd->frontStencilRef, asIs);
                StencilFuncSeparate(BACK,  asIs, cmd->backStencilRef,  asIs);
              }
              break;
            case LINE_WIDTH_COMMAND_NV:
              {
                LineWidthCommandNV* cmd = (LineWidthCommandNV*)current;
                LineWidth(cmd->lineWidth);
              }
              break;
            case POLYGON_OFFSET_COMMAND_NV:
              {
                PolygonOffsetCommandNV* cmd = (PolygonOffsetCommandNV*)current;
                PolygonOffset(cmd->scale,cmd->bias);
              }
              break;
            case ALPHA_REF_COMMAND_NV:
              {
                AlphaRefCommandNV* cmd = (AlphaRefCommandNV*)current;
                AlphaFunc(asIs, cmd->alphaRef);
              }
              break
            case VIEWPORT_COMMAND_NV:
              {
                ViewportCommandNV* cmd = (ViewportCommandNV*)current;
                Viewport  (cmd->x,cmd->y,cmd->width,cmd->height);
              }
              break;
            case SCISSOR_COMMAND_NV:
              {
                ScissorCommandNV* cmd = (ScissorCommandNV*)current;
                Scissor(cmd->x,cmd->y,cmd->width,cmd->height);
              }
              break;
            case FRONT_FACE_COMMAND_NV:
              {
                FrontFaceCommandNV* cmd = (FrontFaceCommandNV*)current;
                FrontFace(cmd->frontFace ? CW : CCW);
              }
              break;
            }

            current = (ubyte *)current + GetTokenSize(header);
          }
          
          return indexType;
        }
    
    None of the commands called by DrawCommandSequenceNV may generate their
    appropriate errors, providing erroneous data as parameters
    or generating state that normally would create errors when executed
    by the server can produce undefined results and may cause program
    termination.
    The residency of all resources referenced directly (buffer addresses inside tokens) 
    or indirectly (texture handles inside uniform buffer objects) must be managed
    explicitly.
    
    
    (XXX should we add something similar to CheckFramebufferStatus? for
     debugging, that tests the content in software and throws error + offset into buffer
     triggering the error)
    
    All BufferAddressRangeNV calls issued by DrawCommandSequenceNV are 
    effective independent of their appropriate client state being enabled or not.

    
    uint GetCommandHeaderNV(enum tokenID, uint size)
    
    Returns the encoded 32bit header value for a given command; the returned
    value is implementation specific.
    The <size> is only provided as basic consistency check, since the size of each 
    structure is fixed and no padding is allowed. The value is the sum of the 
    header and the command specific structure.
    INVALID_ENUM is generated if <tokenID> is not one of the values listed under Table 10.X.2.
    INVALID_VALUE is thrown if the <size> does not match the fixed 
    size of a command defined by the spec.
    
    ushort GetStageIndexNV(enum shadertype)
    
    Returns the 16bit value for a specific shader stage; the returned value
    is implementation specific. The value is to be used with the stage field
    within UniformAddressCommandNV tokens.
    
Add a new subsection 10.X.3 (Drawing with Commands and State Objects)

    State objects may be used in rendering with the commands:

        void DrawCommandsStatesNV(uint buffer, const intptr* indirects, const sizei* sizes, 
                                       const uint* states, const uint* fbos, uint count);
        void DrawCommandsStatesAddressNV(const uint64* indirects, const sizei* sizes, 
                                              const uint* states, const uint* fbos, uint count);

    These commands accept arrays of buffer addresses (either an array of 
    offsets <indirects> into a buffer named by <buffer>, or an array of GPU 
    addresses <indirects>), an array of sequence lengths in <sizes>, and an 
    array of state object names in <states>, of which all names must be non-zero.
    Frame buffer object names are stored in <fbos> and can
    be either zero or non-zero. All arrays have <count> entries.
    The residency of textures used as attachment inside the state object's 
    captured fbo or the passed fbo must managed explicitly. 
    
    INVALID_VALUE is generated if one entry of <states> is zero.
    INVALID_OPERATION is generated if the fbo configuration from <fbos>
    mismatches the configuration inside the corresponding state object
    from <states>.
    
    DrawCommandsStatesNV and DrawCommandsStatesAddressNV are equivalent to:

        Save current GL state;
        enum indexType = UNSIGNED_SHORT;
        for (uint i = 0; i < count; i++) {
            fbo         = LookupFbo(fbos[i]);
            stateObject = LookupStateObject(states[i]);
            
            if ( i == 0){
              Set full state captured by stateObject;
            }
            else {
              Set difference of state going from <states>[i-1] to current stateObject, 
            }
            
            if ( fbo == 0) {
              BindFramebuffer(FRAMEBUFFER, stateObject.fbo.name);
            }
            else if ( stateObject.fbo.configuration == fbo.configuration ){
              // The configuration excludes attachment textures and size information, however
              // includes attached texture formats and other state (see StateCaptureNV).
              
              BindFramebuffer(FRAMEBUFFER, fbo.name);
            }
            else {
              // Only compatible fbo states can be used.
              
              generate ERROR INVALID_OPERATION;
              return;
            }
            
            enum mode = primitive mode from stateObject
        
            uint64 address = address computed from <buffer>+<indirects>[i];
            
            indexType = DrawCommandSequenceNV(mode, indexType, address, sizes[i]);
        }
        Restore current GL state;
    
    where LookupFbo and LookupStateObject return the driver's internal fbo
    and stateObject object and stateObject.fbo is the driver's fbo state
    object and fbo.configuration and fbo.name are the current configuration
    of a fbo and the fbo's name respectively.

Add a new section 10.X.4 (Command Lists)

    A list of DrawCommandsStates* commands may be compiled into a command
    list, for further optimization and efficient reuse. The name space for 
    command lists is the unsigned integers, with zero reserved. The command:

        void CreateCommandListsNV(sizei n, uint *lists);

    returns <n> previously unused command list names in <lists>, and creates
    a command list in the initial state for each name.

    Command lists are deleted by calling

        void DeleteCommandListsNV(sizei n, const uint *lists);

    <lists> contains <n> names of command lists to be deleted. Once a command
    list is deleted it has no contents and its name is again unused. Unused 
    names in <lists> are silently ignored, as is the value zero.

    The command

        void CommandListSegmentsNV(uint list, uint segments);

    indicates that <list> will have <segments> number of segments, each
    of which is a list of command sequences that it enqueues. This must be
    called before any commands are enqueued. In the initial state, a command 
    list has a single segment.

    A command list's initial state allows it to enqueue commands, but not to 
    be executed. The following command can be enqueued:

        void ListDrawCommandsStatesClientNV(uint list, uint segment, const void** indirects, 
                                              const sizei* sizes, const uint* states, const uint* fbos,
                                              uint count);

    A list has multiple segments and each segment enqueues an ordered list of 
    command sequences. This command enqueues the equivalent of the DrawCommandsStatesNV 
    commands into the list indicated by <list> on the segment indicated by <segment> 
    except that the sequence data is copied from the sequences pointed to by the <indirects> 
    pointer. The <indirects> pointer should point to a list of size <count> of pointers, 
    each of which should point to a command sequence. 

    The pre-validated state from <states> is saved into the command list, rather 
    than a reference to the state object (i.e. the state objects or fbos could be 
    deleted and the command list would be unaffected). This includes native
    GPU addresses for all textures indirectly referenced through the fbos
    passed or state objects' fbos attachments, therefore a recompile of the command list
    is required if such referenced textures change their allocation (for example
    due to resizing), as well as explicit management of the residency of
    the textures prior CallCommandListNV.
    
    ListDrawCommandsStatesClientNV performs a by-value copy of the
    indirect data based on the provided client-side pointers. In this case 
    the content is fully immutable, while the buffer-based versions can
    change the content of the buffers at any later time.

    The command

        void CompileCommandListNV(uint list);

    make the list indicated by <list> switch from allowing collection of 
    commands to allowing its execution. At this time, the implementation may
    generate optimized commands to transition between states as efficiently
    as possible. Lists may be executed with the command

        void CallCommandListNV(uint list);

    This executes the command list indicated by <list>, which operates as if
    the DrawCommandsStates* commands were replayed in the order they were 
    enqueued on each segment, starting from segment zero and proceeding to the 
    maximum segment. All buffer or texture resources' residency must be 
    managed explicitly, including texture attachments of the effective 
    fbos during list enqueuing.

    
Modifications to the OpenGL Shading Language Specification, Version 4.40

    Including the following line in a shader can be used to control the
    language features described in this extension:

      #extension GL_NV_command_list : <behavior>

    where <behavior> is as specified in section 3.3.

    New preprocessor #defines are added to the OpenGL Shading Language:

      #define GL_NV_command_list          1
    
    
    Modify Section 4.4.5, "Uniform and Shader Storage Block Layout Qualifiers"

    (modify first paragraph, p.78) Layout qualifiers can be used for uniform
    and shader storage blocks, but not for non-block uniform declarations.
    The layout qualifier identifiers (and shared keyword) for uniform and
    shader storage blocks are

      layout-qualifier-id
        shared
        packed
        std140
        std430
        row_major
        column_major
        binding = integer-constant-expression
        offset  = integer-constant-expression
        align   = integer-constant-expression
        commandBindableNV
    
    (add paragraph prior "When multiple arguments", p. 80) 
    The commandBindableNV qualifier enables the associated uniform block
    to be updated via UniformAddressCommandNVs when executing 
    DrawCommandsStatesNV. When commandBindableNV is enabled the <binding> 
    identifier must be provided for each block, only its value will 
    correspond with the index field of a UniformAddressCommandNV.
    A link time error will be thrown if an index is greater or equal to
    MAX_PROGRAM_PARAMETER_BUFFER_BINDINGS_NV.
    Changing the binding point by the OpenGL API may not influence this 
    associated index value and may cause UniformAddressCommandNVs to have
    undefined behavior.
    
Dependencies on OpenGL 4.4 (Core Profile)

    If only the core profile of OpenGL 4.4 is supported, references to
    functionality deprecated by OpenGL 3.0 (built-in input/output/uniform variables
    corresponding to fixed-function vertex attributes, fixed-function
    vertex and fragment processing) should be removed and/or replaced with 
    functionality supported in the core profile.  In such an environment, the 
    QUADS primitive type is not supported by the StateCaptureNV function. StateCaptureNV will
    also ignore all references to deprecated state such as line stippling.
    The ALPHA_REF_COMMAND_NV is not allowed to be used, therefore GetCommandHeaderNV will
    return an error if the token enum is passed.
    
Interactions with NV_shader_buffer_load
    
    The GPU addresses used in ELEMENT_ADDRESS_COMMAND_NV,
    ATTRIBUTE_ADDRESS_COMMAND_NV and UNIFORM_ADDRESS_COMMAND_NV 
    can be queried via the API provided in this extension. Furthermore
    the same API must be used to ensure residency of such buffers
    when draw commands using such addresses are issued.

Interactions with NV_bindless_texture or ARB_bindless_texture
    
    Residency of fbo attachment textures referenced in state objects
    or command lists must be managed explicitly using the API provided
    by either of these extensions.

Interactions with NV_parameter_buffer_object
  
    The UNIFORM_ADDRESS_COMMAND_NV described in (Drawing with Commands), will affect
    the PROGRAM_PARAMETER_BUFFER of the target stage defined within the command
    token.
 
Interactions with ARB_robust_buffer_access_behavior

    The buffer setups performed by ELEMENT_ADDRESS_COMMAND_NV,
    ATTRIBUTE_ADDRESS_COMMAND_NV and UNIFORM_ADDRESS_COMMAND_NV
    do not provide the required buffer ranges for robust buffer
    access. Therefore draw calls executed under this type of 
    buffer setup will not respect the robust buffer access rules.
    
Interactions with ARB_shader_draw_parameters

    The drawing operations performed through this extension will not support
    setting of the built-in GLSL values that were added by 
    ARB_shader_draw_parameters (gl_BaseInstanceARB, gl_BaseVertexARB, gl_DrawIDARB).
    Accessing these variables will result in undefined values.

Additions to the AGL/GLX/WGL Specifications

    None.

GLX Protocol

    None.

Errors


New State

    None.

Issues

    1) What motivates the design?

    The primary goal is to be able to reuse pre-validated command buffers. Other
    APIs and proposals have addressed this with various incarnations of command 
    lists or state objects, but a recurring problem is that interactions between
    various stages of the pipeline prevent this prevalidation and reuse. These 
    interactions are often hardware-specific (and differ from vendor to vendor 
    or even generation to generation) and new interactions are introduced by 
    new features that were not imagined when the prevalidation scheme was 
    proposed.

    We attempt to address this by having a monolithic state object that 
    encompasses (almost) the entire state of the pipeline. This should provide
    enough information for all implementations to do any needed cross-
    validation. We try to create these in a way that minimizes the new API 
    footprint - since we want ALL state (including any added in the future), we
    just capture it from the current state of the context.

    We expect that a captured state object will be represented as a list of 
    commands to send to the GPU. While that list of commands may be fairly 
    large, it is also well-suited to filtering redundant changes when switching
    from one state object to another (filtering may occur on the GPU, or by 
    some processing on the CPU). We anticipate that filtering will be applied
    when compiling a command list, but it is likely that some (perhaps less 
    aggressive) filtering will also occur in unlisted DrawCommandsStates 
    commands.

    2) Should binding state be captured?

    Binding state should not be captured, for multiple reasons. 
    
    The memory management performed by the driver as part of legacy command 
    execution is expensive and not well-suited for the prevalidation of
    commands. This can be replaced by explicit bindless memory management 
    APIs (e.g. Make*Resident).

    Resource bindings also require behind-the-scenes management of internal
    GPU structures like texture handles. Again, this can be replaced by the 
    bindless APIs.

    3) What FBO state should be captured?

    We definitely want to capture enough information to be able to do any
    state-based recompiles of the fragment shader, which would include 
    drawbuffer state and format state. However, it is not desirable to have
    all properties of the FBO be captured, e.g. if attachment width/height
    were captured then state objects could become invalid if the window shape
    changed 

    RESOLVED: state objects reference the FBO configuration, but passing 
    other compatible FBOs during rendering is possible. Furthermore the
    VIEWPORT_COMMAND_NV allows setting the appropriate viewport state.

    4) Can UBOs be accessed? How?

    RESOLVED: We want to encourage the "first level of the scene graph" information read
    by shaders to be accessed with fast UBO memory accesses. 
    UNIFORM_ADDRESS_COMMAND_NV provides this mechanism.

    5) What about Compute?

    Compute does not have the same complex state interactions that the graphics
    pipeline has, so it is not included in this extension. 

    6) What dynamic state should be allowed?

    There are some state values which are pretty much raw integer/floating 
    point data, where requiring a unique state object for each value would
    drastically bloat the number of state objects needed and break batching.
    We allow for a few such values to be set in the token command buffer 
    rather than in the state object. The current list is motivated by similar
    state in other APIs, and may not be complete.

    7) What are the "segments" in command lists?

    These are multiple "starting points" for appending commands to the list,
    which are ultimately replayed in order by segments. This may be useful to 
    build a multipass rendering algorithm with only a single traversal of the
    scene graph.

    8) When are state objects consumed into the list?

    This could either occur as the command is appended to the list, or during
    CompileCommandListNV.
    
    RESOLVED: At ListDrawCommandsStatesClientNV time.

    9) Do we want to have multiple modes in the same dispatch ?

    RESOLVED: yes, state-objects with different modes can be used, allowing
    fast transitioning between those. Furthermore, it is possible to mix
    LINES/LINE_STRIP/LINE_LOOP or TRIANGLES/TRIANGLE_STRIP/TRIANGLE_FAN and others
    using the same state object, as long as their base primitive mode is the same.
    
    10) Do we want to allow mixing DrawArrays and DrawElements in the same
    dispatch ?

    RESOLVED: yes.
    
    11) What happens if the token buffer is modified while it is being dispatched ?

    RESOLVED: there is no guarantee of coherency, so undefined behavior.
    
    12) I would like to change states in the middle; how do I do this ?
    
    RESOLVED: you can select a new state object or state tokens, but you cannot change
    state in the indirect buffer itself.
    
    13) Is the token buffer multithread safe; does it scale ?
    
    RESOLVED: yes. it is trivial to allocate a token buffer per thread, and then submit
    them in the main thread sequentially. since the implementation is not involved
    when the application writes to them, the only thread safety requirements are in
    the application itself.
    Command lists and state objects are, however, currently not context share-able,
    though as rendering is much more efficient now, the main dispatching thread can
    spend the time on preparing state objects prior drawing. The cost of glStateCaptureNV
    is no worse than a classic API draw call, and exploiting temporal coherence not too
    many states would be "new" frame to frame, but instead cached states can be reused.
    
    14) Can I reuse token buffer multiple times ?
    
    RESOLVED: yes.
     
    15) Should we use a fixed length decoding or at the very least a size in the header ?
    
    RESOLVED: fixed length is used. As basic consistency check the size is also passed to header generation.
    The NOP command can be used to pad structures to custom sizes.

    16) Can I do buffer updates in a single DrawCommands call ?
    
    RESOLVED: NO. 
    Updating memory in general requires synchronization, and having lots of
    updates inside a single DrawCommands would become a performance bottleneck.

    17) I want to implement some occlusion scheme and skip some of the draws; how do I do this ?
    
    RESOLVED: this extension does not offer a conditional render facility, but this can be
    implemented by using NOP or preferably TERMINATE_SEQUENCE commands in the stream.
    
    18) I want to implement some level of detail scheme; is that possible ?
    
    RESOLVED: you can use NOP or TERMINATE_SEQUENCE to skip the level of details that you don't want to draw.

    19) Why can't I just get a token to change the state, and avoid specifying lists of
    state and indirect buffers ?
    
    RESOLVED: Getting a token to specify a state switch imply that the application would
    have access to a virtual address of state changes. This would potentially open security
    issue, since part of the validation may involve complex sequence of programming.

    20) Instead of void** which means all commands must be stored in one buffer, could GLuint64** be used
    when EnableClientState(DRAW_INDIRECT_UNIFIED_NV) is set? This would allow managing different command
    buffers independently.

    RESOLVED: separate Address command added

    21) How big can each indirect command list's buffer size be? 

    RESOLVED: no limit required.

    22) How to retrieve the "index" within UniformAddressCommandNV, or is that the GL binding point?
   
    RESOLVED: added commandBindableNV layout qualifier in GLSL for uniform blocks to ensure fixed binding unit.
    Also added stage value to command.

    23) In what condition is the state left, that is modified by tokens, after the dispatch call?

    RESOLVED: state is reset.
    
    24) How does working with this extension look like
    
    You will find related samples at https://github.com/nvpro-samples
    
    25) How can I use textures, images, shader storage or atomic counter buffers in combination with state objects?

    Textures and images are covered via NV/ARB_bindless_texture, you can store their handles inside uniform buffers.
    Shader storage and atomic counter buffers are currently not directly exposed, however NV_gpu_shader5 allows
    storing pointers to such buffers inside uniform buffers as well. Atomic counters can be replaced by regular
    atomic increments.

    Alternatively use DrawCommandsNV or DrawCommandsAddressNV, which does support any GLSL programs with these
    resource bindings, as well as default-block uniforms.


Revision History

    Rev.    Date      Author    Changes
    ----  --------    --------  -----------------------------------------
     6    11/3/2015   ckubisch  Rephrase what stateobjects capture and what not
     5    8/17/2015   ckubisch  correct errors for DrawCommandsNV and DrawCommandsAddressNV
                                rendering to default framebuffer is not allowed. Clarify
                                which state is inherited (updated Issue 25).
     4    6/18/2015   ckubisch  Add missing interaction with ARB_shader_draw_parameters
     3    5/27/2015   jemmons   Multiple minor fixes and clarifications
     2    4/16/2015   pboudier  Fix incorrect type (size_t is now sizei) in ListDrawCommandsStatesClientNV
     1                pboudier  concept
                      jbolz     base spec
                      ckubisch  detailed spec
                      mjk       Internal revisions