[Mesa-dev] [PATCH 1/8] glsl: optionally declare gl_FragCoord & gl_FrontFacing as system values

[Ian Romanick]

On 01/07/2016 05:29 PM, Marek Olšák wrote:
> From: Marek Olšák <marek.olsak at amd.com>
> 
> ---
>  src/glsl/ast_to_hir.cpp                    |  2 +-
>  src/glsl/builtin_variables.cpp             | 12 ++++++++++--
>  src/glsl/nir/shader_enums.h                |  3 ++-
>  src/mesa/main/mtypes.h                     |  4 ++++
>  src/mesa/state_tracker/st_glsl_to_tgsi.cpp |  1 +
>  5 files changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/src/glsl/ast_to_hir.cpp b/src/glsl/ast_to_hir.cpp
> index e6aec36..f3966d7 100644
> --- a/src/glsl/ast_to_hir.cpp
> +++ b/src/glsl/ast_to_hir.cpp
> @@ -3517,7 +3517,7 @@ get_variable_being_redeclared(ir_variable *var, YYLTYPE loc,
>                state->is_version(150, 0))
>                && strcmp(var->name, "gl_FragCoord") == 0
>                && earlier->type == var->type
> -              && earlier->data.mode == var->data.mode) {
> +              && var->data.mode == ir_var_shader_in) {

I traced this code all the way back to 4a962170d (July 2010!).  I'm not
100% sure why Eric did it this way.  Since earlier->data.mode will
always (before this patch) be ir_var_shader_in, I wonder if this filters
cases like redeclaring gl_FragCoord as an out or a uniform.

Do we have any tests for that?

>        /* Allow redeclaration of gl_FragCoord for ARB_fcc layout
>         * qualifiers.
>         */
> diff --git a/src/glsl/builtin_variables.cpp b/src/glsl/builtin_variables.cpp
> index e82c99e..221aab0 100644
> --- a/src/glsl/builtin_variables.cpp
> +++ b/src/glsl/builtin_variables.cpp
> @@ -1057,8 +1057,16 @@ builtin_variable_generator::generate_fs_special_vars()
>  {
>     ir_variable *var;
>  
> -   add_input(VARYING_SLOT_POS, vec4_t, "gl_FragCoord");
> -   add_input(VARYING_SLOT_FACE, bool_t, "gl_FrontFacing");
> +   if (this->state->ctx->Const.GLSLFragCoordIsSysVal)
> +      add_system_value(SYSTEM_VALUE_FRAG_COORD, vec4_t, "gl_FragCoord");
> +   else
> +      add_input(VARYING_SLOT_POS, vec4_t, "gl_FragCoord");
> +
> +   if (this->state->ctx->Const.GLSLFrontFacingIsSysVal)
> +      add_system_value(SYSTEM_VALUE_FRONT_FACE, bool_t, "gl_FrontFacing");
> +   else
> +      add_input(VARYING_SLOT_FACE, bool_t, "gl_FrontFacing");
> +
>     if (state->is_version(120, 100))
>        add_input(VARYING_SLOT_PNTC, vec2_t, "gl_PointCoord");
>  
> diff --git a/src/glsl/nir/shader_enums.h b/src/glsl/nir/shader_enums.h
> index 0be217c..8a2a81a 100644
> --- a/src/glsl/nir/shader_enums.h
> +++ b/src/glsl/nir/shader_enums.h
> @@ -412,7 +412,8 @@ typedef enum
>      * \name Fragment shader system values
>      */
>     /*@{*/
> -   SYSTEM_VALUE_FRONT_FACE,     /**< (not done yet) */
> +   SYSTEM_VALUE_FRAG_COORD,
> +   SYSTEM_VALUE_FRONT_FACE,
>     SYSTEM_VALUE_SAMPLE_ID,
>     SYSTEM_VALUE_SAMPLE_POS,
>     SYSTEM_VALUE_SAMPLE_MASK_IN,
> diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
> index 5b9fce8..126b272 100644
> --- a/src/mesa/main/mtypes.h
> +++ b/src/mesa/main/mtypes.h
> @@ -3515,6 +3515,10 @@ struct gl_constants
>      */
>     GLboolean GLSLSkipStrictMaxUniformLimitCheck;
>  
> +   /** Whether gl_FragCoord and gl_FrontFacing are system values. */
> +   bool GLSLFragCoordIsSysVal;
> +   bool GLSLFrontFacingIsSysVal;
> +
>     /**
>      * Always use the GetTransformFeedbackVertexCount() driver hook, rather
>      * than passing the transform feedback object to the drawing function.
> diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> index 6cbc26a..9308eb4 100644
> --- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> +++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
> @@ -4459,6 +4459,7 @@ const unsigned _mesa_sysval_to_semantic[SYSTEM_VALUE_MAX] = {
>  
>     /* Fragment shader
>      */
> +   TGSI_SEMANTIC_POSITION,
>     TGSI_SEMANTIC_FACE,
>     TGSI_SEMANTIC_SAMPLEID,
>     TGSI_SEMANTIC_SAMPLEPOS,
>