[Mesa-dev] [PATCH] gallium: add bits for clipping points as tris (d3d-style)

[Erik Faye-Lund]

On Fri, Jan 10, 2014 at 10:33 AM, Lauri Kasanen <cand at gmx.com> wrote:
> On Fri, 10 Jan 2014 03:57:45 +0100
> sroland at vmware.com wrote:
>
>> From: Roland Scheidegger <sroland at vmware.com>
>>
>> OpenGL does whole-point clipping, that is a large point is either fully
>> clipped or fully unclipped (the latter means it may extend beyond the
>> viewport as long as the center is inside the viewport). d3d9 (d3d10 has
>> no large points) however requires points to be clipped after they are
>> expanded to a rectangle. (Note some IHVs are known to ignore GL rules at
>> least with some hw/drivers.)
>>
>> Hence add a rasterizer bit indicating which way points should be clipped
>> (some drivers probably will always ignore this), and add the draw interaction
>> this requires. Drivers wanting to support this and using draw must support
>> large points on their own as draw doesn't implement vp clipping on the
>> expanded points (it potentially could but the complexity doesn't seem
>> warranted), and the driver needs to do viewport scissoring on such points.
>
> Is there any possibility of this being exposed to user-space? With that
> hat on, it would have been useful to me several times in the past.
>
> Perhaps whoever was Mesa's ARB contact could propose an extension? I
> know nothing about how that happens, just would like this functionality.

IIRC there were some draft by NVIDIA discussed in Khronos OpenGL ES
meetings 6-7 years ago, but I don't think it ever resulted in a
released extension spec.