[Mesa-dev] [PATCH 7/8] i965/msaa: Adjust MCS buffer allocation for 8x MSAA.

[Paul Berry]

On 24 July 2012 12:10, Kenneth Graunke <kenneth at whitecape.org> wrote:

> On 07/18/2012 09:21 AM, Paul Berry wrote:
> > MCS buffers use 32 bits per pixel in 8x MSAA, and 8 bits per pixel in
> > 4x MSAA.  This patch adjusts the format we use to allocate the buffer
> > so that enough memory is set aside for 8x MSAA.
> > ---
> >  src/mesa/drivers/dri/intel/intel_mipmap_tree.c |   27
> ++++++++++++++++++++++-
> >  1 files changed, 25 insertions(+), 2 deletions(-)
> >
> > diff --git a/src/mesa/drivers/dri/intel/intel_mipmap_tree.c
> b/src/mesa/drivers/dri/intel/intel_mipmap_tree.c
> > index d6572cd..f30f92b 100644
> > --- a/src/mesa/drivers/dri/intel/intel_mipmap_tree.c
> > +++ b/src/mesa/drivers/dri/intel/intel_mipmap_tree.c
> > @@ -672,7 +672,30 @@ intel_miptree_alloc_mcs(struct intel_context *intel,
> >  {
> >     assert(mt->mcs_mt == NULL);
> >     assert(intel->gen >= 7); /* MCS only used on Gen7+ */
> > -   assert(num_samples == 4); /* TODO: support 8x MSAA */
> > +
> > +   /* Choose the correct format for the MCS buffer.  All that really
> matters
> > +    * is that we allocate the right buffer size, since we'll always be
> > +    * accessing this miptree using MCS-specific hardware mechanisms,
> which
> > +    * infer the correct format based on num_samples.
> > +    */
> > +   gl_format format;
> > +   switch (num_samples) {
> > +   case 4:
> > +      /* 8 bits/pixel are required for MCS data when using 4x MSAA (2
> bits for
> > +       * each sample).
> > +       */
> > +      format = MESA_FORMAT_A8;
>
> I'm surprised to see A8 here...it would be nicer, I think, to use R8.  I
> guess all that matters here is that you get an 8-bit, 1-component
> format...but the luminance/alpha formats are pretty awful and require
> special cases in a lot of places, so I'd rather avoid using them
> wherever possible.
>
> That said, I would change it in a separate patch.
>

Ok, will do.  Thanks for the review.


>
> > +      break;
> > +   case 8:
> > +      /* 32 bits/pixel are required for MCS data when using 8x MSAA (3
> bits
> > +       * for each sample, plus 8 padding bits).
> > +       */
> > +      format = MESA_FORMAT_R_UINT32;
> > +      break;
> > +   default:
> > +      assert(!"Unrecognized sample count in intel_miptree_alloc_mcs");
> > +      break;
> > +   };
> >
> >     /* From the Ivy Bridge PRM, Vol4 Part1 p76, "MCS Base Address":
> >      *
> > @@ -684,7 +707,7 @@ intel_miptree_alloc_mcs(struct intel_context *intel,
> >      */
> >     mt->mcs_mt = intel_miptree_create(intel,
> >                                       mt->target,
> > -                                     MESA_FORMAT_A8,
> > +                                     format,
> >                                       mt->first_level,
> >                                       mt->last_level,
> >                                       mt->width0,
> >
>
>
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