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

[Matt Turner]

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.

Basically the same thing occurs later in the patch (I do see it was
just moved from elsewhere).