[Mesa-dev] [RFC PATCH 23/40] i965/fs: Associate the uniform location for the fragment shader

[Kenneth Graunke]

On Sunday, January 04, 2015 04:04:37 PM Abdiel Janulgue wrote:
> Signed-off-by: Abdiel Janulgue <abdiel.janulgue at linux.intel.com>
> ---
>  src/mesa/drivers/dri/i965/brw_fs.cpp | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
> index 3639ed2..0f2c2c4 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
> @@ -1144,6 +1144,7 @@ fs_visitor::setup_uniform_values(ir_variable *ir)
>           continue;
>        }
>  
> +      brw->uniformstagemap[u] |= _NEW_FRAGMENT_CONSTANTS;
>        unsigned slots = storage->type->component_slots();
>        if (storage->array_elements)
>           slots *= storage->array_elements;
> 

You can't just put a giant array in brw_context and index it by uniform
numbers like this.  Every shader program has its own set of uniforms.

Let's say I use two shader programs:

Program A is:

   [vertex shader]
   uniform mat4 mvp;
   void main() { gl_Position = mvp * gl_Vertex; }

   [fragment shader]
   void main() { gl_FragColor = vec4(1.0); }

Program B is:

   [vertex shader]
   void main() { gl_Position = gl_Vertex; }

   [fragment shader]
   uniform vec4 color;
   void main() { gl_FragColor = color; }

In program A, "mvp" will be uniform 0.  In program B, "color" will be
uniform 0.  Your single global map will contain:

brw->uniformstagemap[0] == _NEW_VERTEX_CONSTANTS | _NEW_FRAGMENT_CONSTANTS

which is wrong - each program has distinct uniforms that are each only used
in a single stage.

I think the approach I recommended in my reply to patch 19 should solve this
without the need for the global table.
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