angle/extensions/ANGLE_base_vertex_base_instance_shader_builtin.txt

Name

    ANGLE_base_vertex_base_instance_shader_builtin

Name Strings

    GL_ANGLE_base_vertex_base_instance_shader_builtin

Contributors

    Shrek Shao, Google Inc.
    Contributors to the ANGLE_base_vertex_base_instance specification
    Contributors to the ARB_shader_draw_parameters specification

Contact

    Shrek Shao (shrekshao 'at' google.com)

Status

    Incomplete

Version

    Last Modified Date: Nov 19, 2021
    Author Revision: 1

Number

    OpenGL ES Extension XX

Dependencies

    The extension is based on ANGLE_base_vertex_base_instance, all limitations of which
    apply to this extension.

Overview

    This extension is based on ANGLE_base_vertex_base_instance. It should be enabled
    only if ANGLE_base_vertex_base_instance is enabled.

    Additional to the functionality exposed by ANGLE_base_vertex_base_instance,
    <gl_BaseVertex> and <gl_BaseInstance> builtins are added to the shading language.
    For any *BaseVertex* draw call variant, the <baseVertex> of the draw may be
    read by the vertex shader as <gl_BaseVertex>. For non *BaseVertex* calls,
    the value of <gl_BaseVertex> is 0.
    For any *BaseInstance draw call variant, the baseInstance of the draw may
    be read by the vertex shader as <gl_BaseInstance>. For non *BaseInstance
    calls, the value of <gl_BaseInstance> is 0.

IP Status

    No known IP claims.

New Procedures and Functions

    None.

New Tokens

    None.

Additions to Chapter 10 of the OpenGL ES 3.2 Specification

    Section 10.5 Drawing Commands Using Vertex Arrays:

    The base index of the instance may be read by a vertex shader as
    <gl_BaseInstance>, for the commands

    void DrawArraysInstancedBaseInstanceANGLE (GLenum mode,
        GLint first,
        GLsizei count,
        GLsizei instanceCount,
        GLuint baseInstance);

    and

    void MultiDrawArraysInstancedBaseInstanceANGLE(GLenum mode,
        const GLint* firsts,
        const GLsizei* counts,
        const GLsizei* instanceCounts,
        const GLuint* baseInstances,
        GLsizei drawcount);

    The base index of the vertex may be read by a vertex shader as
    <gl_BaseVertex>. This value is also added to the <gl_VertexID>.

    The base index of the instance may be read by a vertex shader as
    <gl_BaseInstance>. Note that this value is not added to the
    <gl_InstanceID>, for the commands

    void DrawElementsInstancedBaseVertexBaseInstanceANGLE (GLenum mode,
        GLsizei count,
        GLenum type,
        const GLvoid* indices,
        GLsizei instanceCount,
        GLint baseVertex,
        GLuint baseInstance);

    and

    void MultiDrawElementsInstancedBaseVertexBaseInstanceANGLE(GLenum mode,
        const GLsizei* counts,
        GLenum type,
        const GLvoid* const* indices,
        const GLsizei* instanceCounts,
        const GLint* baseVertices,
        const GLuint* baseInstances,
        GLsizei drawcount);

Errors

    None.

Modifications to the OpenGL ES Shading Language Specification, Version 3.00

    Including the following line in a shader controls the
    language featured described in this extension:

      #extension GL_ANGLE_base_vertex_base_instance_shader_builtin : <behavior>

    where <behavior> is as specified in section 3.5.

    A new preprocessor #define is added to the OpenGL ES Shading Language:

      #define GL_ANGLE_base_vertex_base_instance_shader_builtin 1


Issues

    None

Revision History

    Rev.    Date    Author       Changes
    ----  --------  ----------   --------------------------------------------
    1     11/19/21   Shrek Shao   First revision.