[Mesa-dev] [PATCH] glsl: Don't require gl_Position to be written in GLSL 1.40.

[Kenneth Graunke]

On 03/19/2012 11:05 PM, Eric Anholt wrote:
> ---
>   src/glsl/linker.cpp |   35 ++++++++++++++++++++++++++++++-----
>   1 files changed, 30 insertions(+), 5 deletions(-)
>
> diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
> index 39169aa..471525e 100644
> --- a/src/glsl/linker.cpp
> +++ b/src/glsl/linker.cpp
> @@ -258,11 +258,36 @@ validate_vertex_shader_executable(struct gl_shader_program *prog,
>      if (shader == NULL)
>         return true;
>
> -   find_assignment_visitor find("gl_Position");
> -   find.run(shader->ir);
> -   if (!find.variable_found()) {
> -      linker_error(prog, "vertex shader does not write to `gl_Position'\n");
> -      return false;
> +   /* From the GLSL 1.10 spec, page 48:
> +    *
> +    *     "The variable gl_Position is available only in the vertex
> +    *      language and is intended for writing the homogeneous vertex
> +    *      position. All executions of a well-formed vertex shader
> +    *      executable must write a value into this variable. [...] The
> +    *      variable gl_Position is available only in the vertex
> +    *      language and is intended for writing the homogeneous vertex
> +    *      position. All executions of a well-formed vertex shader
> +    *      executable must write a value into this variable."
> +    *
> +    * while in GLSL 1.40 this text is changed to:
> +    *
> +    *     "The variable gl_Position is available only in the vertex
> +    *      language and is intended for writing the homogeneous vertex
> +    *      position. It can be written at any time during shader
> +    *      execution. It may also be read back by a vertex shader
> +    *      after being written. This value will be used by primitive
> +    *      assembly, clipping, culling, and other fixed functionality
> +    *      operations, if present, that operate on primitives after
> +    *      vertex processing has occurred. Its value is undefined if
> +    *      the vertex shader executable does not write gl_Position."
> +    */
> +   if (prog->Version<  140) {
> +      find_assignment_visitor find("gl_Position");
> +      find.run(shader->ir);
> +      if (!find.variable_found()) {
> +	 linker_error(prog, "vertex shader does not write to `gl_Position'\n");
> +	 return false;
> +      }
>      }
>
>      prog->Vert.ClipDistanceArraySize = 0;

Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>