[Mesa-dev] [PATCH] svga: fix blending regression

[Ilia Mirkin]

Can st/mesa instead be fixed to maintain the original API? Other
drivers look in rt[0] in the non-independent_blend_enable case. For
example, freedreno and nouveau.

On Wed, Feb 28, 2018 at 10:29 AM, Brian Paul <brianp at vmware.com> wrote:
> The earlier Mesa commit 3d06c8afb5 ("st/mesa: don't translate blend
> state when it's disabled for a colorbuffer") subtly changed the
> details of gallium's per-RT blend state.
>
> In particular, when pipe_rt_blend_state[i].blend_enabled is true,
> we have to get the src/dst blend terms from pipe_rt_blend_state[i],
> not [0] as before.
>
> We now have to scan the blend targets to find the first one that's
> enabled (if any).  We have to use the index of that target for getting
> the src/dst blend terms.  And note that we have to set identical blend
> terms for all targets.
>
> This fixes the Piglit fbo-drawbuffers2-blend test.  VMware bug 2063493.
> ---
>  src/gallium/drivers/svga/svga_pipe_blend.c | 35 ++++++++++++++++++++----------
>  1 file changed, 24 insertions(+), 11 deletions(-)
>
> diff --git a/src/gallium/drivers/svga/svga_pipe_blend.c b/src/gallium/drivers/svga/svga_pipe_blend.c
> index 04855fa..6bb9d94 100644
> --- a/src/gallium/drivers/svga/svga_pipe_blend.c
> +++ b/src/gallium/drivers/svga/svga_pipe_blend.c
> @@ -148,6 +148,17 @@ svga_create_blend_state(struct pipe_context *pipe,
>     if (!blend)
>        return NULL;
>
> +   /* Find index of first target with blending enabled.  -1 means blending
> +    * is not enabled at all.
> +    */
> +   int first_enabled = -1;
> +   for (i = 0; i < PIPE_MAX_COLOR_BUFS; i++) {
> +      if (templ->rt[i].blend_enable) {
> +         first_enabled = i;
> +         break;
> +      }
> +   }
> +
>     /* Fill in the per-rendertarget blend state.  We currently only
>      * support independent blend enable and colormask per render target.
>      */
> @@ -260,24 +271,26 @@ svga_create_blend_state(struct pipe_context *pipe,
>           }
>        }
>        else {
> -         /* Note: the vgpu10 device does not yet support independent
> -          * blend terms per render target.  Target[0] always specifies the
> -          * blending terms.
> +         /* Note: the vgpu10 device does not yet support independent blend
> +          * terms per render target.  When blending is enabled, the blend
> +          * terms must match for all targets.
>            */
> -         if (templ->independent_blend_enable || templ->rt[0].blend_enable) {
> -            /* always use the 0th target's blending terms for now */
> +         if (first_enabled >= 0) {
> +            /* use first enabled target's blending terms */
> +            const struct pipe_rt_blend_state *rt = &templ->rt[first_enabled];
> +
>              blend->rt[i].srcblend =
> -               svga_translate_blend_factor(svga, templ->rt[0].rgb_src_factor);
> +               svga_translate_blend_factor(svga, rt->rgb_src_factor);
>              blend->rt[i].dstblend =
> -               svga_translate_blend_factor(svga, templ->rt[0].rgb_dst_factor);
> +               svga_translate_blend_factor(svga, rt->rgb_dst_factor);
>              blend->rt[i].blendeq =
> -               svga_translate_blend_func(templ->rt[0].rgb_func);
> +               svga_translate_blend_func(rt->rgb_func);
>              blend->rt[i].srcblend_alpha =
> -               svga_translate_blend_factor(svga, templ->rt[0].alpha_src_factor);
> +               svga_translate_blend_factor(svga, rt->alpha_src_factor);
>              blend->rt[i].dstblend_alpha =
> -               svga_translate_blend_factor(svga, templ->rt[0].alpha_dst_factor);
> +               svga_translate_blend_factor(svga, rt->alpha_dst_factor);
>              blend->rt[i].blendeq_alpha =
> -               svga_translate_blend_func(templ->rt[0].alpha_func);
> +               svga_translate_blend_func(rt->alpha_func);
>
>              if (blend->rt[i].srcblend_alpha != blend->rt[i].srcblend ||
>                  blend->rt[i].dstblend_alpha != blend->rt[i].dstblend ||
> --
> 2.7.4
>
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