GLSL_NV_ray_tracing_motion_blur

Name

    NV_ray_tracing_motion_blur

Name Strings

    GL_NV_ray_tracing_motion_blur

Contact
    Eric Werness (ewerness 'at' nvidia.com), NVIDIA
    Ashwin Lele  (alele 'at' nvidia.com), NVIDIA

Contributors

    Daniel Koch, NVIDIA

Status

    Complete

Version

    Last Modified Date: 2023-04-06
    Revision: 2

Dependencies

    This extension can be applied to OpenGL GLSL versions 4.60
    (#version 460) and higher.

    This extension is written against revision 5 of the OpenGL Shading Language
    version 4.60, dated September 4, 2017.

    This extension requires GLSL_EXT_ray_tracing and interacts with
    GLSL_NV_ray_tracing.


Overview

    This extension extends the GLSL support added for ray tracing in
    GLSL_EXT_ray_tracing extension to expose a new overloaded variant of built-in
    function call for recursive ray traversal 'traceRayMotionNV' and a new built-in
    variable 'gl_CurrentRayTimeNV' which can be used to calculate shading
    based on ray geometry intersection at a particular point in time.

    Mapping to SPIR-V
    -----------------

    For informational purposes (non-normative), the following is an
    expected way for an implementation to map GLSL constructs to SPIR-V
    constructs:

      gl_CurrentRayTimeNV -> CurrentRayTimeNV decorated OpVariable

      traceRayMotionNV -> OpTraceRayMotionNV instruction

Modifications to the OpenGL Shading Language Specification, Version 4.60

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

      #extension GL_NV_ray_tracing_motion_blur                    : 

    where  is as specified in section 3.3.
    New preprocessor #defines are added:

      #define GL_NV_ray_tracing_motion_blur                      1

Additions to Chapter 7 of the OpenGL Shading Language Specification
(Built-in Variables)

    Modify Section 7.1, Built-in Languages Variables

    (Add to the list of builtin variables)

    In the intersection, any-hit, closest-hit and miss shading languages,
    following additional built-in variables are declared as follows

        in    float  gl_CurrentRayTimeNV;

    Add the following description for gl_CurrentRayTimeNV:

    The input variable gl_CurrentRayTimeNV is available in the intersection,
    any-hit, closest-hit and miss languages and provides the time parameter
    as passed to the parent 'traceRayMotionNV' call. Result is undefined if
    parent call was 'traceNV' or 'traceRayEXT'.


Additions to Chapter 8 of the OpenGL Shading Language Specification
(Built-in Functions)

    (Modify Section 8.19, Ray Tracing Functions)

    (Add following built-in)

Syntax:

    void traceRayMotionNV(accelerationStructureEXT topLevel,
                   uint rayFlags,
                   uint cullMask,
                   uint sbtRecordOffset,
                   uint sbtRecordStride,
                   uint missIndex,
                   vec3 origin,
                   float Tmin,
                   vec3 direction,
                   float Tmax,
                   float currentTime,
                   int payload);

    This function is only available in the ray generation, closest hit, and
    miss shaders.

    'traceRayMotionNV' operates the same as 'traceRayEXT', with the exception of
     parameter.

    The  parameter is an additional parameter provided to
    traversal call when compared with 'traceRayEXT'. It can be queried in
    downstream stages to implement time-dependent behavior (like geometry transformations)
    and is used to intersect with motion geometry at the corresponding time.


Interactions with GLSL_NV_ray_tracing

    'accelerationStructureNV' and 'accelerationStructureEXT' are aliases and
    use same SPIR-V opcodes so they can be used interchangeably for 'traceRayMotionNV'

    'rayPayloadNV' and 'rayPayloadEXT' storage classes are aliases and so are
    'rayPayloadInNV' and 'rayPayloadInEXT' so variables decorated with location with
    these storage classes can be used interchangeably as compile-time constant
    argument for the 'payload' parameter for 'traceRayMotionNV'.



Issues

    TBD

Revision History

    Rev.  Date          Author     Changes
    ----  -----------   ------     -------------------------------------------
     2    2023-04-06    ewerness   Fix misnamed builtin in overview
     1    2021-07-01    alele      Internal revisions.