[Mesa-dev] [PATCH 2/3] glsl: Fix incorrect hard-coded location of the gl_SecondaryFragColorEXT built-in.

[Ilia Mirkin]

On Mon, Aug 22, 2016 at 9:59 PM, Francisco Jerez <currojerez at riseup.net> wrote:
> gl_SecondaryFragColorEXT should have the same location as gl_FragColor
> for the secondary fragment color to be replicated to all fragment
> outputs.  The incorrect location of gl_SecondaryFragColorEXT would
> cause the linker to mark both FRAG_RESULT_COLOR and FRAG_RESULT_DATA0
> as being written to, which isn't allowed by the spec and would
> ultimately lead to an assertion failure in
> fs_visitor::emit_fb_writes() on my i965-fb-fetch branch.

My recollection was that it didn't work with COLOR for "stupid"
reasons. Can you confirm that
bin/arb_blend_func_extended-fbo-extended-blend-pattern_gles2 -auto
passes with this patch?

>
> This should also fix the code below for multiple dual-source-blended
> render targets, which no driver currently supports but we have plans
> to enable eventually in the i965 driver (the comment saying that no
> hardware will ever support it seems rather hilarious).
> ---
>  src/compiler/glsl/builtin_variables.cpp | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/src/compiler/glsl/builtin_variables.cpp b/src/compiler/glsl/builtin_variables.cpp
> index cb5f730..b29f677 100644
> --- a/src/compiler/glsl/builtin_variables.cpp
> +++ b/src/compiler/glsl/builtin_variables.cpp
> @@ -1145,13 +1145,8 @@ builtin_variable_generator::generate_fs_special_vars()
>     }
>
>     if (state->es_shader && state->language_version == 100 && state->EXT_blend_func_extended_enable) {
> -      /* We make an assumption here that there will only ever be one dual-source draw buffer
> -       * In case this assumption is ever proven to be false, make sure to assert here
> -       * since we don't handle this case.
> -       * In practice, this issue will never arise since no hardware will support it.
> -       */
> -      assert(state->Const.MaxDualSourceDrawBuffers <= 1);
> -      add_index_output(FRAG_RESULT_DATA0, 1, vec4_t, "gl_SecondaryFragColorEXT");
> +      add_index_output(FRAG_RESULT_COLOR, 1, vec4_t,
> +                       "gl_SecondaryFragColorEXT");
>        add_index_output(FRAG_RESULT_DATA0, 1,
>                         array(vec4_t, state->Const.MaxDualSourceDrawBuffers),
>                         "gl_SecondaryFragDataEXT");
> --
> 2.9.0
>
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