[Mesa-dev] [PATCH] i965: Fix clear code for ignoring colormask for XRGB formats on Gen9+.

[Pohjolainen, Topi]

On Thu, Apr 21, 2016 at 10:00:57AM +0200, Iago Toral wrote:
> On Wed, 2016-04-20 at 18:38 -0700, Kenneth Graunke wrote:
> > In commit cda886a4851ab767fba40e8474d6fa8190347e4f, Neil made us stop
> > advertising RGBX formats on Gen9+, as the hardware apparently no longer
> > has working fast clear support for those formats.  Instead, we just
> > fall back to RGBA formats, and use SCS to override alpha to 1.0.
> > 
> > This is fine, but had one unintended side effect: it made us fall back
> > to slow clears when the color mask disables alpha.  Normally, we ignore
> > the color mask for non-existent channels.  This includes alpha for XRGB
> > formats as writing garbage to the X channel is harmless.  But, now that
> > we use RGBA, we think there's a real alpha channel, and can't do the
> > optimization.
> > 
> > To hack around this, check if _BaseFormat is GL_RGB and ignore alpha.
> > 
> > Improves WebGL Aquarium performance on Skylake GT3e by about 50%
> > by letting it use repclears instead of slow clears.
> > 
> > Cc: Ben Widawsky <ben at bwidawsk.net>
> > Cc: Topi Pohjolainen <topi.pohjolainen at intel.com>
> > Cc: mesa-stable at lists.freedesktop.org
> > Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> > ---
> >  src/mesa/drivers/dri/i965/brw_meta_fast_clear.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > 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 1fb5dc8..5d89294 100644
> > --- a/src/mesa/drivers/dri/i965/brw_meta_fast_clear.c
> > +++ b/src/mesa/drivers/dri/i965/brw_meta_fast_clear.c
> > @@ -645,6 +645,7 @@ brw_meta_fast_clear(struct brw_context *brw, struct gl_framebuffer *fb,
> >        GLubyte *color_mask = ctx->Color.ColorMask[buf];
> >        for (int i = 0; i < 4; i++) {
> >           if (_mesa_format_has_color_component(irb->mt->format, i) &&
> > +             !(i == 3 && irb->Base.Base._BaseFormat == GL_RGB) &&
> 
> I was wondering if we could generalize the fix so we just ignore any
> channels that are not present in the base format. Something like this:
> 
> i <= _mesa_base_format_component_count(irb->Base.Base._BaseFormat)

Only problem is that "irb->Base.Base._BaseFormat" is not mesa_format but
Glenum.