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

[Brian Paul]

On 02/28/2018 08:36 AM, Ilia Mirkin wrote:
> 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.

If independent blend is not in use, then rt[0] will have all the 
blending info, as before.

The case that broke for us was when PIPE_CAP_INDEP_BLEND_FUNC==0 and 
independent blend was enabled for rt[i] where i > 0.  Before, the blend 
src/dst terms were in rt[0] but now they're in rt[i].

I'd rather not change the semantics again.

-Brian

> 
> 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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