[Mesa-dev] [PATCH 4/9] anv: Added support for non-dynamic sample locations on Gen8+

[Eleni Maria Stea]

On Wed, 13 Mar 2019 08:16:10 -0500
Jason Ekstrand <jason at jlekstrand.net> wrote:

> On Mon, Mar 11, 2019 at 10:05 AM Eleni Maria Stea <estea at igalia.com>
> wrote:
> 
> > Allowing the user to set custom sample locations non-dynamically, by
> > filling the extension structs and chaining them to the pipeline
> > structs according to the Vulkan specification section [26.5. Custom
> > Sample Locations]

[...]

> > +void
> > +anv_calc_sample_locations(struct anv_sample *samples,
> > +                          uint32_t num_samples,
> > +                          const VkSampleLocationsInfoEXT *info)
> > +{
> > +   int i;
> > +
> > +   for(i = 0; i < num_samples; i++) {
> > +      float dx, dy;
> > +
> > +      /* this is because the grid is 1x1, in case that
> > +       * we support different grid sizes in the future
> > +       * this must be changed.
> > +       */
> > +      samples[i].offs_x = info->pSampleLocations[i].x;
> > +      samples[i].offs_y = info->pSampleLocations[i].y;
> > +
> > +      /* distance from the center */
> > +      dx = samples[i].offs_x - 0.5;
> > +      dy = samples[i].offs_y - 0.5;
> > +
> > +      samples[i].radius = dx * dx + dy * dy;
> > +   }
> > +
> > +   qsort(samples, num_samples, sizeof *samples, compare_samples);
> >  
> 
> Are we allowed to re-order the samples like this?  The spec says:
> 
> The sample location for sample i at the pixel grid location (x,y) is
> taken from pSampleLocations[(x + y * sampleLocationGridSize.width) *
> sampleLocationsPerPixel + i]
> 
> Which leads me to think that they expect the ordering of samples to be
> respected.  Yes, I know the HW docs say we're supposed to order them
> from nearest to furthest.  However, AFAIK, that's only so we get nice
> centroids and I don't know that it's actually required.
> 
> --Jason

I wasn't sure about this to be honest. I could remove the qsort and
explain why we decided to ignore the PRM in a comment for the case that
someone decides to put this back in the future.

Thanks a lot for reviewing the series, BTW. I am working on the
changes for all patches.

Eleni