[Mesa-dev] [PATCH 0/6] Add support for GL_NV_fill_rectangle

[Marek Olšák]

On Thu, Mar 23, 2017 at 7:45 PM, Lyude Paul <lyude at redhat.com> wrote:
> On Thu, 2017-03-23 at 14:22 -0400, Alex Deucher wrote:
>> On Thu, Mar 23, 2017 at 2:18 PM, Marek Olšák <maraeo at gmail.com>
>> wrote:
>> > Is there any user of this extension?
>>
>> Based on the spec, it seems like it would be useful for glamor.  No
>> idea is anyone has code to use it yet.
> Actually me, robclark and airlied were talking specifically about using
> this for glamor and trying to implement it on other platforms using
> rectangular primitives. No idea if that'll work (especially since I'm
> new here), but it sounds promising enough to try :).
>
> Once I get this patch series upstream I'll probably look into writing
> an implementation for softpipe and some other drivers

Well radeons can't support or emulate the NV extension, so this is all
just for nouveau. I doubt that airlied would want a nouveau-only
codepath in glamor.

Below is my definition of what a hypothetical MESA_rectangle_primitive
should specify. It takes into account all we know about existing
desktop hardware (AMD - we have the hw spec; Intel - I talked with
them; NV - I read the NV fill extension).


Definition and behavior:
- The rectangle primitive is defined by its first 3 vertices.
- The 4th vertex is derived (extrapolated) during rasterization.
- It's treated as a triangle by all stages before rasterization.
- The rectangle edges must be parallel or perpendicular to X and Y
axes, i.e. the rectangle can only be rotated in 90-degree increments
and flipped over.
- It must be rasterized as a rectangle (no diagonal tearing allowed,
no artifacts on the diagonal allowed)
- The content of gl_FrontFacing is undefined.

Return a GL error:
- if clip planes, clip distances, or cull distances are enabled.
- if face culling is enabled. (face determination is undefined)
- if polygon mode is not fill
- if primitive restart is enabled
- if geometry or tessellation shaders are enabled

The behavior is undefined:
- if the rectangle edges are not axis-aligned.
- if Z coordinates of all 3 vertices are not equal.
- if the rectangle intersects the clip space boundaries. (all options
are allowed: clip, cull, or accept the primitive)
- if two-sided lighting is enabled and the colors are not the same for
both sides.

TODO:
- Add piglit to verify that the order of vertices doesn't matter on Intel.


Marek