[Mesa-dev] [PATCH 2/2] gallium: Replaced gl_rasterization_rules with lower_left_origin and half_pixel_center.

[Jose Fonseca]

----- Original Message -----
> On 21.04.2013 12:34, Dave Airlie wrote:
> > On Sun, Apr 21, 2013 at 5:36 PM, Jose Fonseca <jfonseca at vmware.com> wrote:
> >> ----- Original Message -----
> >>> Do we really need the lower_left_origin state? I think I can't
> >>> implement it for radeon and it's the kind of stuff that should be
> >>> taken care of by the state tracker anyway.
> >> My understanding is that hardware had switches for this sort of thing.
> >> It's really hard to provide fully-conforming rasterization for opengl,
> >> dx9 & dx10 without it.
> >>
> >> If your hardware allows to put a negative pitch on rendertargets, then
> >> that should also do it.
> >>
> >> If you know what is the hardware's sub-pixel rasterization resolution,
> >> then adding a vertical bias equal to that amount, depending on this
> >> state, would give a very close approximation. (This would get the
> >> top/bottom edges right, at expense of small inaccuracies on
> >> non-horizontal edges)
> >>
> >>> Isn't it sufficient to just
> >>> set a viewport which is upside down, like we do now?
> >> I'm not aware of rasterization top-left rule being affected by the
> >> viewport flipping.
> >>
> >> Do both
> >>
> >>  ./bin/triangle-rasterization -auto
> >>  ./bin/triangle-rasterization -use_fbo -auto
> >>
> >> currently work for you?
> >>
> > just FYI, on my evergreen, the first fails the second passes, maybe
> > someone could try on fglrx, I'd be sorta willing to guess AMD hw just
> > does DX10 :)
> >
> > and I think I've heard some complaints about our rendering offseting
> > being wrong somewhere in the past on r600.

This really just affects a corner cases -- where edges are perfectly horizontal and go precisely through the pixel center -- but there might be apps out there that draw a lot of screen aligned rectangles, and end up hitting this more often than one would imagine. (For example, GL based UI/HTML rendering engine at 50% zoom).

> Same on nouveau. On NV blob it's the other way around, it fails for
> -use_fbo. So clearly, both can work.

Interesting.  Whenever I tested with NVIDIA proprietary drivers (and I did it on more than one driver version / hw), both cases always passed.

This is what I just tested:

  OpenGL vendor string: NVIDIA Corporation
  OpenGL renderer string: Quadro K1000M/PCIe/SSE2
  OpenGL version string: 4.3.0 NVIDIA 310.14
  OpenGL shading language version string: 4.30 NVIDIA via Cg compiler

Jose