kc3-lang/angle/extensions/CHROMIUM_bind_uniform_location.txt

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• Author : Olli Etuaho
  Date : 2018-03-23 14:36:39
  Hash : 44861c48
  Message : Clarify aliasing rules in CHROMIUM_bind_uniform_location The CHROMIUM_bind_uniform_location spec previously had some conflicting information on when uniform location aliasing was allowed. Now the section on uniform location aliasing makes it clear that aliasing locations of two statically used uniforms is an error. This guarantees compatibility between different compiler versions that may treat a different subset of uniforms as active, depending on optimizations. It follows the spirit of GLSL ES 3.00.6 spec section 12.46, that has similar rules for attributes. The implementation is fixed to correctly follow the spec. When flattening uniforms, static use is tracked separately from activeness. BUG=angleproject:2262 TEST=angle_end2end_tests Change-Id: I570fd384064aec66ef0380a53fa01ac5e43eec5a Reviewed-on: https://chromium-review.googlesource.com/978144 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>

• extensions/CHROMIUM_bind_uniform_location.txt

• Name
  
      CHROMIUM_bind_uniform_location
  
  Name Strings
  
      GL_CHROMIUM_bind_uniform_location
  
  Version
  
      Last Modifed Date: September 8, 2015
  
  Dependencies
  
      OpenGL ES 2.0 is required.
  
  Overview
  
      This extension is simlar to glBindAttribLocation but instead
      lets you choose a location for a uniform. This allows you
      to not have to query the locations of uniforms.
  
      This allows the client program to know the locations of uniforms
      without having to wait for shaders to compile or GLSL programs to
      link to query the locations and therefore have no blocking calls
      when initializing programs.
  
  Issues
  
      If a uniform is an array you can only call glBindUniformLocation
      for the location of the first element. Other elements' locations
      must be queried if you need them. Often this is not an issue
      because you can set all the elements with a single gl call from
      the first location.
  
      Good Example:
  
          --shader--
          uniform float u_someArray[4];
  
          --C--
          GLint location = 123;
          glBindUniformLocation(program, location, "u_someArray");
          glLinkProgram(program);
          glUseProgram(program);
  
          // set all 4 floats in u_someArray
          float values[] = { 0.1f, 0.2f, 0.3f, 0.4f, };
          glUniform1fv(location, 4, values);
  
      Bad example 1:
  
          GLint location = 123;
          glBindUniformLocation(program, location, "u_someArray");
          glLinkProgram(program);
          glUseProgram(program);
  
          // set floats in u_someArray one at a time
          glUniform1f(location, 0.1f);
          glUniform1f(location + 1, 0.2f);  // ERROR! math not allowed on locations
  
      Bad example 2:
  
          GLint location0 = 123;
          GLint location1 = 124;
          glBindUniformLocation(program, location0, "u_someArray[0]");
          glBindUniformLocation(program, location1, "u_someArray[1]"); // ERROR!
          // not allowed to assign locations to array elements
  
      If you need to set individual elements of a uniform array you must query the
      location of the each element you wish to set.
  
      If a uniform has its location explicitly set within the shader text and a
      different location set via the API, the assignment in the shader text is
      used.
  
      If the location of a statically used uniform set via the API conflicts with
      the location of a different uniform set in the shader text, linking must
      fail.
  
  New Tokens
  
      None
  
  New Procedures and Functions
  
      void BindUniformLocationCHROMIUM (GLuint program, GLint location,
                                        const GLhchar* name);
  
      specifes that the uniform variable named <name> in program <program>
      should be bound to uniform location <location> when the program is next
      linked.  If <name> was bound previously, its assigned binding is replaced
      with <location>. <name> must be a null terminated string.  The error
      INVALID_VALUE is generated if <location> is equal or greater than
  
      (MAX_VERTEX_UNIFORM_VECTORS + MAX_FRAGMENT_UNIFORM_VECTORS) * 4
  
      or less than 0. BindUniformLocation has no effect until the program is
      linked. In particular, it doesn't modify the bindings of uniform
      variables in a program that has already been linked.
  
      The error INVALID_OPERATION is generated if name starts with the reserved
      "gl_" prefix. The error INVALID_VALUE is generated if name ends with
      an array element expression other than "[0]".
  
      When a program is linked, any active uniforms without a binding specified
      through BindUniformLocation will be automatically be bound to locations by
      the GL.  Such bindings can be queried using the command
      GetUniformLocation.
  
      BindUniformLocation may be issued before any shader objects are attached
      to a program object.  Hence it is allowed to bind any name (except a name
      starting with "gl_") to an index, including a name that is never used as a
      uniform in any shader object.  Assigned bindings for uniform variables
      that do not exist or are not active are ignored. Using such bindings
      behaves as if passed location was -1.
  
      It is possible for an application to bind more than one uniform name to
      the same location.  This is referred to as aliasing.  This will only work
      if only one of the aliased uniforms is statically used in the executable
      program.  If two statically used uniforms in a program are bound to the same
      location, link must fail.
  
  Errors
  
      None.
  
  New State
  
      None.
  
  Revision History
  
      7/20/2012    Documented the extension
      9/8/2015     Require program link to fail if two statically used uniforms
                   are bound to the same location.
      11/6/2015    Require inactive and non-existing, bound uniform locations
                   to behave like location -1.
      3/9/2017     Locations set in the shader override ones set by the binding
                   API.
      3/26/2018    Clarify that aliasing rules apply to statically used uniforms.