[Mesa-dev] [PATCH] i965: fix alpha test for MRT

[Paul Berry]

On 1 July 2013 04:45, Chris Forbes <chrisf at ijw.co.nz> wrote:

> Include src0 alpha in the RT write message when using MRT, so it is used
> for the alpha test instead of the normal per-RT alpha value.
>
> Fixes broken rendering in Dota2 under Wine [FDO #62647] -- but not
> tested against much else.
>
> Signed-off-by: Chris Forbes <chrisf at ijw.co.nz>
>


Since there's no other user of key.sample_alpha_to_coverage, I guess I'd
prefer to see it renamed to something like key.replicate_alpha, and then in
brw_wm_populate_key(), set it to "ctx->DrawBuffer->_NumColorDrawBuffers > 1
&& (ctx->Multisample.SampleAlphaToCoverage || ctx->Color.AlphaEnabled)".
That will reduce unnecessary recompiles.

Also it would be nice to have a piglit test for this--it seems like the
sort of thing we could easily regress in the future if we're not careful.


> ---
>  src/mesa/drivers/dri/i965/brw_fs_emit.cpp    | 2 +-
>  src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 2 +-
>  src/mesa/drivers/dri/i965/brw_wm.c           | 4 ++++
>  src/mesa/drivers/dri/i965/brw_wm.h           | 1 +
>  4 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_emit.cpp
> b/src/mesa/drivers/dri/i965/brw_fs_emit.cpp
> index f390989..10f4c99 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_emit.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_emit.cpp
> @@ -129,7 +129,7 @@ fs_generator::generate_fb_write(fs_inst *inst)
>
>           if (inst->target > 0 &&
>              c->key.nr_color_regions > 1 &&
> -            c->key.sample_alpha_to_coverage) {
> +            (c->key.sample_alpha_to_coverage || c->key.alpha_test)) {
>              /* Set "Source0 Alpha Present to RenderTarget" bit in message
>               * header.
>               */
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> index a67b6ed..0c8dc1b 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
> @@ -2255,7 +2255,7 @@ fs_visitor::emit_fb_writes()
>        src0_alpha_to_render_target = intel->gen >= 6 &&
>                                     !do_dual_src &&
>                                     c->key.nr_color_regions > 1 &&
> -                                   c->key.sample_alpha_to_coverage;
> +                                   (c->key.sample_alpha_to_coverage ||
> c->key.alpha_test);
>        /* m2, m3 header */
>        nr += 2;
>     }
> diff --git a/src/mesa/drivers/dri/i965/brw_wm.c
> b/src/mesa/drivers/dri/i965/brw_wm.c
> index 6eb4a1d..3265596 100644
> --- a/src/mesa/drivers/dri/i965/brw_wm.c
> +++ b/src/mesa/drivers/dri/i965/brw_wm.c
> @@ -279,6 +279,8 @@ brw_wm_debug_recompile(struct brw_context *brw,
>                        old_key->nr_color_regions, key->nr_color_regions);
>     found |= key_debug(intel, "sample alpha to coverage",
>                        old_key->sample_alpha_to_coverage,
> key->sample_alpha_to_coverage);
> +   found |= key_debug(intel, "MRT alpha test w/a",
> +                      old_key->alpha_test, key->alpha_test);
>     found |= key_debug(intel, "rendering to FBO",
>                        old_key->render_to_fbo, key->render_to_fbo);
>     found |= key_debug(intel, "fragment color clamping",
> @@ -463,6 +465,8 @@ static void brw_wm_populate_key( struct brw_context
> *brw,
>     key->nr_color_regions = ctx->DrawBuffer->_NumColorDrawBuffers;
>    /* _NEW_MULTISAMPLE */
>     key->sample_alpha_to_coverage = ctx->Multisample.SampleAlphaToCoverage;
> +   /* _NEW_COLOR */
> +   key->alpha_test = ctx->Color.AlphaEnabled;
>
>     /* BRW_NEW_VUE_MAP_GEOM_OUT */
>     if (intel->gen < 6)
> diff --git a/src/mesa/drivers/dri/i965/brw_wm.h
> b/src/mesa/drivers/dri/i965/brw_wm.h
> index 28e8734..13b17d0 100644
> --- a/src/mesa/drivers/dri/i965/brw_wm.h
> +++ b/src/mesa/drivers/dri/i965/brw_wm.h
> @@ -63,6 +63,7 @@ struct brw_wm_prog_key {
>     GLuint flat_shade:1;
>     GLuint nr_color_regions:5;
>     GLuint sample_alpha_to_coverage:1;
> +   GLuint alpha_test:1;
>     GLuint render_to_fbo:1;
>     GLuint clamp_fragment_color:1;
>     GLuint line_aa:2;
> --
> 1.8.3.2
>
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