Name

    AMD_occlusion_query_event

Name Strings

    GL_AMD_occlusion_query_event

Contact

    Graham Sellers (graham.sellers 'at' amd.com)

Contributors

    Graham Sellers, AMD
    Daniel Rakos, AMD

Status

    SHIPPING

Version

    Last Modified Date:         11/20/2013
    Author Revision:            3

Number

    OpenGL Extension #442

Dependencies

    OpenGL 1.5 is required.

    This extension is written against the OpenGL 4.4 (core) specification.

    This extension depends on the definition of OpenGL 3.3 and
    GL_ARB_occlusion_query2.

    This extension depends on the definition of OpenGL 4.3 and
    GL_ARB_ES3_compatibility.

    This extension depends on the definition of GL_EXT_depth_bounds_test.

Overview

    Occlusion queries provide a means to count the number of fragments that
    pass the depth and stencil tests and that may contribute to a rendered
    image. In unextended OpenGL, an occlusion query increments its
    samples-passed count whenever a sample passes both the stencil test and
    the depth test (if enabled). However, there is no way to count fragments
    that fail the stencil test, or pass the stencil test and then subsequently
    fail the depth test.

    This extension introduces the concept of occlusion query events and changes
    the concept of an occlusion query from counting passed fragments to counting
    fragments that generate any of a user-selectable set of events. Provided
    events include passing the depth test, and passing or failing the stencil
    test. For a given occlusion query object, counting of these events may be
    enabled or disabled, allowing any combination to be counted.

New Procedures and Functions

        void QueryObjectParameteruiAMD(enum target,
                                       uint id,
                                       enum pname,
                                       uint param);

New Tokens

    Accepted by the <pname> argument to QueryObejctParameteruiAMD,
    GetQueryObjectiv, GetQueryObjectuiv, GetQueryObjecti64v, and
    GetQueryObjectui64v:

        OCCLUSION_QUERY_EVENT_MASK_AMD                      0x874F

    Accepted by the <param> argument to QueryObjectParameteruiAMD:

        QUERY_DEPTH_PASS_EVENT_BIT_AMD                      0x00000001
        QUERY_DEPTH_FAIL_EVENT_BIT_AMD                      0x00000002
        QUERY_STENCIL_FAIL_EVENT_BIT_AMD                    0x00000004
        QUERY_DEPTH_BOUNDS_FAIL_EVENT_BIT_AMD               0x00000008
        QUERY_ALL_EVENT_BITS_AMD                            0xFFFFFFFF

Additions to Chapter 4 of the OpenGL 4.4 (core) Specification (Event Model)

    Insert Section 4.2.1, "Query Object Parameters", p.42. Renumber subsequent
    sections.

    Query object parameters control the behavior of the query object. Changing
    the value of a query object parameter is done by calling

        void QueryObjectParameteruiAMD(enum target,
                                       uint id,
                                       enum pname,
                                       uint param);

    with <target> set to a valid query target, <id> set to a value returned
    from a previous call to GenQueries. <pname> specifies the parameter to
    modify and <param> contains its new value. If <id> is an unused query object
    name then the name is marked as used and associated with a new query object
    of the type specified by <target>. Otherwise, <id> must be the name of an
    existing query object of that type.

Additions to Chapter 17 of the OpenGL 4.3 (core) Specification (Writing Fragments
and Samples to the Framebuffer)

    Modify the first paragraph of Subection 17.3.7, "Occlusion Queries" as
    follows:

    Occlusion queries use query objects to track fragments as they pass through
    the depth bounds test, stencil test and depth test, in that order. Each
    stage may generate an event. An event is generated if a fragment fails
    the depth bounds test. If a fragment passes the depth bounds test, it then
    undergoes the stencil test and generates an event should it fail that.
    Should it pass the stencil test, it undergoes the depth test, upon which
    it will generate an event indicating whether it passed or failed the depth
    test. An occlusion query can be started and finished by calling BeginQuery
    and EndQuery, respectively, with a <target> of SAMPLES_PASSED,
    ANY_SAMPLES_PASSED, or ANY_SAMPLES_PASSED_CONSERVATIVE.

    In the remainder of the Subsection, replace any occurrence of "passes the
    depth test" with "generates an enabled event". Add the following to the end
    of the subsection:

    Counting of occlusion query events are enabled and disabled for a query
    object by calling QueryObjectParameteruiAMD with <target> set to
    SAMPLES_PASSED, ANY_SAMPLES_PASSED or ANY_SAMPLES_PASSED_CONSERVATIVE, with
    <id> set to the name of an existing query object of the appropriate type, or
    to a name returned from a call to GenQueries but not yet associated with a
    query object, with <pname> set to OCCLUSION_QUERY_EVENT_MASK_AMD and with
    <param> set to the bitwise or of the set of the following flags:

      +---------------------------------------+---------------------------------------------------------+
      | QUERY_DEPTH_PASS_EVENT_BIT_AMD        | Indicates that the fragment passed all tests.           |
      | QUERY_DEPTH_FAIL_EVENT_BIT_AMD        | Indicates that the fragment passed the depth bounds and |
      |                                       | stencil tests, but failed the depth test.               |
      | QUERY_STENCIL_FAIL_EVENT_BIT_AMD      | Indicates that the fragment passed the depth bounds     |
      |                                       | test but failed the stencil test.                       |
      | QUERY_DEPTH_BOUNDS_FAIL_EVENT_BIT_AMD | Indicates that the fragment failed the depth bounds     |
      |                                       | test.                                                   |
      | QUERY_ALL_EVENT_BITS_AMD              | Indicates that any event generated by the fragment      |
      |                                       | should be counted.                                      |
      +---------------------------------------+---------------------------------------------------------+

    By default, the value of OCCLUSION_QUERY_EVENT_MASK_AMD for a newly created
    occlusion query object is QUERY_DEPTH_PASS_EVENT_BIT_AMD.

Additions to the AGL/GLX/WGL Specifications

    None.

GLX Protocol

    None.

Errors

    INVALID_OPERATION is generated by GetQueryObjectiv, GetQueryObjectuiv,
    GetQueryObjecti64v, and GetQueryObjectui64v if <pname> is
    OCCLUSION_QUERY_EVENT_MASK_AMD and the target of the query object
    specified by <id> is not SAMPLES_PASSED, ANY_SAMPLES_PASSED, or
    ANY_SAMPLES_PASSED_CONSERVATIVE.

    INVALID_ENUM is generated by QueryObjectParameteruiAMD if <target> is not
    an accepted query target.

    INVALID_ENUM is generated by QueryObjectParameteruiAMD if <pname> is not
    OCCLUSION_QUERY_EVENT_MASK_AMD.

    INVALID_VALUE is generated by QueryObjectParameteruiAMD if <id> is not a
    name returned from a previous call to GenQueries, or if such a name has
    since been deleted with DeleteQueries.

    INVALID_OPERATION is generated by QueryObjectParameteruiAMD if <id> is the
    name of an existing query object whose target does not match <target>, or
    an active query object name for <target>.

    INVALID_OPERATION is generated by QueryObjectParameteruiAMD if <pname> is
    OCCLUSION_QUERY_EVENT_MASK_AMD and <target> is not SAMPLES_PASSED,
    ANY_SAMPLES_PASSED, or ANY_SAMPLES_PASSED_CONSERVATIVE.

    INVALID_VALUE is generated by QueryObjectParameteruiAMD if <pname> is
    OCCLUSION_QUERY_EVENT_MASK_AMD and <param> contains any unsupported bits,
    except in the case when <param> is equal to the special value,
    QUERY_ALL_EVENT_BITS_AMD.

New State

    Append to Table 23.44, "Query Object State"

    +-----------------------------------+-------+--------------------+--------------------------------+------------------------------------+--------+
    | Get Value                         | Type  | Get Command        | Initial Value                  | Description                        | Sec.   |
    +-----------------------------------+-------+--------------------+--------------------------------+------------------------------------+--------+
    | OCCLUSION_QUERY_EVENT_MASK_AMD    | Z+    | GetQueryObjectuiv  | QUERY_DEPTH_PASS_EVENT_BIT_AMD | Bitmask of events to count in an   | 17.3.7 |
    |                                   |       |                    |                                | occlusion query                    |        |
    +-----------------------------------+-------+--------------------+--------------------------------+------------------------------------+--------+

New Implementation Dependent State

    None.

Usage Examples

    TBD

Dependencies on GL_EXT_depth_bounds_test

    If GL_EXT_depth_bounds_test is not supported, remove any reference to
    the depth bounds test and the QUERY_DEPTH_BOUNDS_FAIL_EVENT_BIT_AMD token.
    The value of the QUERY_DEPTH_BOUNDS_FAIL_EVENT_BIT_AMD remains reserved, however.
    This extension shall behave as if all fragments pass the depth bounds
    test.

Dependencies on OpenGL 3.3 and GL_ARB_occlusion_query2

    If GL_ARB_occlusion_query2 is not present, and the GL version is less than
    3.3, then remove any reference to the ANY_SAMPLES_PASSED target.

Dependencies on OpenGL 4.3 and GL_ARB_ES3_compatibility

    If GL_ARB_ES3_compatility is not present, and the GL version is less than
    4.3, then remove any reference to the ANY_SAMPLES_PASSED_CONSERVATIVE
    target.

Issues

    1) Why is there no QUERY_STENCIL_PASS_BIT_AMD or
       QUERY_DEPTH_BOUNDS_PASS_BIT_AMD?

       Fragments that pass the depth bounds test proceed to the stencil test
       and subsequently to the depth test. The sum of depth pass, depth fail
       and stencil fail is, by definition, the number of fragments that pass
       the depth bounds test. Likewise, the sum of depth pass and depth fail
       is the number of fragments that pass the stencil test. Thus, setting
       the event mask to (QUERY_DEPTH_PASS_EVENT_BIT_AMD |
       QUERY_DEPTH_FAIL_EVENT_BIT_AMD | QUERY_STENCIL_FAIL_EVENT_BIT_AMD)
       allows counting of fragments that pass the depth bounds test. Similarly,
       setting the event mask to (QUERY_DEPTH_PASS_EVENT_BIT_AMD |
       QUERY_DEPTH_FAIL_EVENT_BIT_AMD) provides the count of fragments that pass
       the stencil test.

    2) Will fragments that fail the stencil test generate a depth pass or fail
       event as if they were depth tested? Will fragments that fail the depth
       bounds test generate stencil fail events?

       RESOLVED: No. Once a fragment fails testing at a particular stage, it
       is discarded and cannot generate any more events.

    3) What happens if the implementation doesn't support EXT_depth_bounds.

       RESOLVED: It is as if all fragments pass the depth bounds test. No
       depth bounds failed events are generated.

    4) What is the purpose of QUERY_ALL_EVENT_BITS_AMD?

       RESOLVED: It allows the counting of all fragments that are subjected to
       any test regardless of the outcome of those tests.

    5) What should the new query state setter function be called?

       DISCUSSION: Unfortunately, the query object API doesn't really follow
       the naming conventions of object state getters already, as
       GetQueryObject should have been rather called GetQueryParameter.
       We considered the following options:

        (a) QueryObjectuiAMD
        (b) QueryParameteruiAMD
        (c) QueryObjectParameteruiAMD

       Option (a) follows the existing naming convention of the query object
       API, but is too general.
       Option (b) follows the naming convention of other object types, but
       because the getter of existing query states is called GetQueryObject,
       while there is also a GetQuery getter that returns context state,
       not per-query object state.
       Option (c) doesn't follow either the naming convention of the query
       object API or any other object type's, but rather a mixture of the two,
       however, it makes explicit both the fact that the setter operates
       on a query object and that it modifies its parameter.

       RESOLVED: QueryObjectParameteruiAMD, because the function modifies
       a state/parameter of a query object.

    6) Should there be also a GetQueryObjectParameteruiAMD?

       RESOLVED: No. GetQueryObject is already defined to query the state of
       a query object (see also issue #5).

Revision History

    Rev.    Date      Author    Changes
    ----  --------    --------  ---------------------------------------------
      3   11/20/2013  gsellers  Make ready for posting
      2   08/20/2013  drakos    Internal revision
      1   10/08/2012  gsellers  Initial revision