[Mesa-dev] [PATCH 7/8] i965/fs: Add support for TXD with shadow comparisons on gen4-6.

[Eric Anholt]

On Wed, 15 Jun 2011 01:24:54 -0700, Kenneth Graunke <kenneth at whitecape.org> wrote:
> Gen4-6 don't have a sample_d_c message, so we have to do a regular
> sample_d and emit instructions to manually perform the comparison.
> 
> This requires a state dependent recompile whenever ctx->Depth.Func
> changes.  do_wm_prog looks for a compiled program in the cache based off
> of brw_wm_prog_key, and if it doesn't find one, recompiles.  So we
> simply need to add the depth comparison function to the key; the
> _NEW_DEPTH dirty bit was already in-place.

> diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> index 03687ce..67344bd 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> @@ -744,7 +744,7 @@ fs_visitor::emit_texture_gen5(ir_texture *ir, fs_reg dst, fs_reg coordinate,
>     }
>     mlen += ir->coordinate->type->vector_elements * reg_width;
>  
> -   if (ir->shadow_comparitor) {
> +   if (ir->shadow_comparitor && ir->op != ir_txd) {
>        mlen = MAX2(mlen, header_present + 4 * reg_width);
>  
>        this->result = reg_undef;
> @@ -934,6 +934,21 @@ fs_visitor::visit(ir_texture *ir)
>     int sampler = _mesa_get_sampler_uniform_value(ir->sampler, prog, &fp->Base);
>     sampler = fp->Base.SamplerUnits[sampler];
>  
> +   /* Pre-Ivybridge doesn't have a sample_d_c message, so shadow compares
> +    * for textureGrad/TXD need to be emulated with instructions.
> +    */
> +   bool hw_compare_supported = ir->op != ir_txd || intel->gen > 7;
> +   if (ir->shadow_comparitor && !hw_compare_supported) {
> +      /* Mark that this program is only valid for the current glDepthFunc */
> +      c->key.depth_compare_func = ctx->Depth.Func;

The compiler is only called if the key wasn't found in the cache, so you
can't set the key inside the compiler :)

> +
> +      /* No need to even sample for GL_ALWAYS or GL_NEVER...bail early */
> +      if (ctx->Depth.Func == GL_ALWAYS)
> +	 return swizzle_shadow_result(ir, fs_reg(1.0f), sampler);
> +      else if (ctx->Depth.Func == GL_NEVER)
> +	 return swizzle_shadow_result(ir, fs_reg(0.0f), sampler);
> +   }

Generally I use "c->key." values to make it obvious that state dependent
recompiles are in place, instead of "ctx->".  

> diff --git a/src/mesa/drivers/dri/i965/brw_wm.h b/src/mesa/drivers/dri/i965/brw_wm.h
> index e244b55..0b284b6 100644
> --- a/src/mesa/drivers/dri/i965/brw_wm.h
> +++ b/src/mesa/drivers/dri/i965/brw_wm.h
> @@ -67,6 +67,7 @@ struct brw_wm_prog_key {
>     GLuint alpha_test:1;
>     GLuint clamp_fragment_color:1;
>     GLuint line_aa:2;
> +   uint8_t depth_compare_func; /* 0 if irrelevant, GL_LESS etc. otherwise */

Wow, those do happen to fit in 8 bits.  Might comment that explicitly --
leaving out bits when storing GLenums has been a common bug and seeing
things like this make me paranoid and go check :)
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