[Mesa-dev] [PATCH 05/10] i965/meta/gen9: Individually fast clear color attachments

[Matt Turner]

On Tue, Oct 13, 2015 at 9:12 PM, Matt Turner <mattst88 at gmail.com> wrote:
> On Tue, Oct 13, 2015 at 8:50 PM, Ben Widawsky
> <benjamin.widawsky at intel.com> wrote:
>> The impetus for this patch comes from a seemingly benign statement within the
>> spec (quoted within the patch). For me, this patch was at some point critical
>> for getting stable piglit results (though this did not seem to be the case on a
>> branch Chad was working on).
>>
>> It is very important for clearing multiple color buffer attachments and can be
>> observed in the following piglit tests:
>> spec/arb_framebuffer_object/fbo-drawbuffers-none glclear
>> spec/ext_framebuffer_multisample/blit-multiple-render-targets 0
>>
>> Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
>> ---
>>  src/mesa/drivers/dri/i965/brw_meta_fast_clear.c | 97 +++++++++++++++++++++----
>>  1 file changed, 84 insertions(+), 13 deletions(-)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_meta_fast_clear.c b/src/mesa/drivers/dri/i965/brw_meta_fast_clear.c
>> index 7bf52f0..9e6711e 100644
>> --- a/src/mesa/drivers/dri/i965/brw_meta_fast_clear.c
>> +++ b/src/mesa/drivers/dri/i965/brw_meta_fast_clear.c
>> @@ -427,6 +427,74 @@ use_rectlist(struct brw_context *brw, bool enable)
>>     brw->ctx.NewDriverState |= BRW_NEW_FRAGMENT_PROGRAM;
>>  }
>>
>> +/**
>> + * Individually fast clear each color buffer attachment. On previous gens this
>> + * isn't required. The motivation for this comes from one line (which seems to
>> + * be specific to SKL+). The list item is in section titled _MCS Buffer for
>> + * Render Target(s)_
>> + *
>> + *   "Since only one RT is bound with a clear pass, only one RT can be cleared
>> + *   at a time. To clear multiple RTs, multiple clear passes are required."
>> + *
>> + * The code follows the same idea as the resolve code which creates a fake FBO
>> + * to avoid interfering with too much of the GL state.
>> + */
>> +static void
>> +fast_clear_attachments(struct brw_context *brw,
>> +                       struct gl_framebuffer *fb,
>> +                       uint32_t fast_clear_buffers,
>> +                       struct rect fast_clear_rect)
>> +{
>> +   assert(brw->gen >= 9);
>> +   struct gl_context *ctx = &brw->ctx;
>> +
>> +   GLuint old_fb = ctx->DrawBuffer->Name;
>> +
>> +   for (unsigned buf = 0; buf < fb->_NumColorDrawBuffers; buf++) {
>> +      struct gl_renderbuffer *rb = fb->_ColorDrawBuffers[buf];
>> +      struct intel_renderbuffer *irb = intel_renderbuffer(rb);
>> +      GLuint fbo, rbo;
>> +      int index = fb->_ColorDrawBufferIndexes[buf];
>> +
>> +      if (!((1 << index) & fast_clear_buffers))
>
> Small suggestion: I think this would read better as
> ((fast_clear_buffers & (1 << index)) != 0.

Oops, sorry -- of course I meant ((fast_clear_buffers & (1 << index)) == 0.