kc3-lang/angle/extensions/ANGLE_provoking_vertex.txt

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• Hash : 27727e50
  Author :
  Date : 2022-11-21T00:00:00
  

  Fix ProvokingVertex typos
  
  Aligned the parameter name with the upstream specs
  
  Moved ValidateProvokingVertexANGLE to validationESEXT.cpp
  
  Bug: angleproject:2829
  Change-Id: I820a90c20ef0a1873640c933b1de52526cac7e70
  Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4043701
  Reviewed-by: Jamie Madill <jmadill@chromium.org>
  Reviewed-by: Geoff Lang <geofflang@chromium.org>
  Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com>
  

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• extensions/ANGLE_provoking_vertex.txt

• Name
  
      ANGLE_provoking_vertex
  
  Name Strings
  
      GL_ANGLE_provoking_vertex
  
  Status
  
      Complete
  
  Version
  
      Last Modified Date: Nov 1, 2022
      Author Revision: 1
  
  Number
  
      OpenGL ES Extension XX
  
  Dependencies
  
      OpenGL ES 3.0 is required.
  
      This extension is written against the OpenGL ES 3.0 specification.
  
      OES_geometry_shader and EXT_geometry_shader interact with this extension.
  
  Overview
  
      This extension provides an alternative provoking vertex convention
      for rendering lines and triangles.
  
      The provoking vertex of a primitive is the vertex that determines the
      constant output values when "flat" interpolation qualifier is used.
  
      In OpenGL ES, the provoking vertex for triangle, line, and (trivially)
      point primitives is the last vertex used to assemble the primitive.
  
      Alternatively the provoking vertex could be the first vertex of
      the primitive. Other APIs have adopted the "first vertex of the
      primitive" convention to determine the provoking vertex.
  
      The motivation for this extension is to allow convention-agnostic
      applications to have better performance when running on top of layered
      implementations of OpenGL ES (such as ANGLE) that use native APIs with
      the "first vertex of the primitive" provoking vertex convention.
  
  New Procedures and Functions
  
      void ProvokingVertexANGLE(enum provokeMode);
  
  New Tokens
  
      Accepted by the <provokeMode> parameter of ProvokingVertex:
  
          FIRST_VERTEX_CONVENTION_ANGLE             0x8E4D
          LAST_VERTEX_CONVENTION_ANGLE              0x8E4E
  
      Accepted by the <pname> parameter of GetBooleanv, GetIntegerv,
      GetFloatv, and GetDoublev:
  
          PROVOKING_VERTEX_ANGLE                    0x8E4F
  
  Additions to Chapter 2 of the OpenGL ES 3.0 Specification (OpenGL ES Operation)
  
      Modify Section 2.17 "Flatshading"
  
      (replace Table 2.12)
  
                                   First vertex  Last vertex
      Primitive type of polygon i  convention    convention
      ===========================  ============  =============
      point                             i        i
  
      independent line                  2i-1     2i
      line loop                         i        i+1, if i<n
                                                 1,   if i==n
      line strip                        i        i+1
  
      independent triangle              3i-2     3i
      triangle strip                    i        i+2
      triangle fan                      i+1      i+2
  
      line adjacency                    4i-2     4i-1
      line strip adjacency              i+1      i+2
      triangle adjacency                6i-5     6i-1
      triangle strip adjacency          2i-1     2i+3
  
      Table 2.12: Provoking vertex selection. The output values used for
      flatshading the <i>th primitive generated by drawing commands with the
      indicated primitive type are derived from the corresponding values of
      the vertex whose index is shown in the table. Vertices are numbered 1
      through n, where n is the number of vertices drawn.
  
      (add after the second paragraph)
  
      The provoking vertex is controlled with the command
  
         void ProvokingVertexANGLE(enum provokeMode);
  
      <provokeMode> must be either FIRST_VERTEX_CONVENTION_ANGLE or
      LAST_VERTEX_CONVENTION_ANGLE, and controls selection of the vertex whose
      values are assigned to varying outputs, as shown in Table 2.12.
  
      The state required for flatshading is one bit for the provoking vertex
      mode. The initial value of the provoking vertex mode is
      LAST_VERTEX_CONVENTION_ANGLE.
  
  Dependencies on OES_geometry_shader, EXT_geometry_shader, and/or the geometry
  shader functionality integrated into the core by OpenGL ES 3.2:
  
      If none of OES_geometry_shader, EXT_geometry_shader, or OpenGL ES 3.2
      are supported:
         * ignore the rows of table 2.12 for line adjacency, line strip
           adjacency, triangle adjacency, and triangle strip adjacency.
  
  Errors
  
      INVALID_ENUM is generated when ProvokingVertexANGLE is called with a
      <provokeMode> that is not either FIRST_VERTEX_CONVENTION_ANGLE or
      LAST_VERTEX_CONVENTION_ANGLE.
  
  New State
  
  (add a new table "Coloring" after the table 6.5)
  
  Get Value               Type  Get Command  Initial Value                 Description       Sec
  ----------------        ----  -----------  ----------------------------  ----------------  ----
  PROVOKING_VERTEX_ANGLE  Z2    GetIntegerv  LAST_VERTEX_CONVENTION_ANGLE  Provoking vertex  2.17
                                                                              convention
  
  Revision History
  
      11/1/2022   First revision
  

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