[Mesa-dev] [PATCH] meta: Use result of texture coordinate clamping operation

[Ian Romanick]

On 09/09/2015 04:55 PM, Anuj Phogat wrote:
> On Wed, Sep 9, 2015 at 11:30 AM, Ian Romanick <idr at freedesktop.org> wrote:
>> I'm pretty sure our implementation of this extension is complete
>> rubbish.  I have attached an image from the blit-scaled test.  This
>> result cannot be useful to anyone.
>>
> Paul Berry and I agreed to follow the "NVIDIA Implementation Details"
> given in the extension spec. i965 driver currently use bilinear filtering
> for both SCALED_RESOLVE_FASTEST and SCALED_RESOLVE_NICEST.
> Do you think the implementation doesn't match what is suggested in
> the spec? I'll be happy to work on improving the implementation if you
> have any specific comments.
> 
> Extension spec mentions the potential loss of quality when using a
> single pass scaled resolve blit. Also the quality of image generated
> depends on sample count and scaling factor. I vaguely remember
> Paul mentioned the scaling factor of ~1.5, beyond which single pass
> scaled resolve blit quickly becomes useless. I think the attached
> image is using a scaling factor of 2.4.

Yes, I think so.  It was the last image produced by the test.

> I'm attaching an old image generated by me doing the quality
> comparison with Nvidia's proprietary driver implementation. I posted
> the image on mesa-dev before enabling the extension on i965. Please
> see the images under "New implementation" for the comparison.

Comparing our images with NVIDIA's image, I don't see very much
difference.  That's both reassuring and depressing.  Looking at all of
those images, I can't imagine why anyone would bother using this
functionality.  I doubt there's any scenario where the little "spikes"
that grow of the sides of the triangles is acceptable.  Oh well.