[Mesa-dev] [PATCH 1/2] mesa : MESA_framebuffer_flip_y extension

Ilia Mirkin imirkin at alum.mit.edu
Thu Jun 7 23:47:13 UTC 2018

On Thu, Jun 7, 2018 at 7:31 PM, Fritz Koenig <frkoenig at google.com> wrote:
> On Thu, Jun 7, 2018 at 4:10 PM Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>> It's slightly different than what you've specified, but can't you
>> achieve this with GL_ARB_clip_control / GL_EXT_clip_control ?
> It can be, but there is a lot of extra work that needs to be done to
> get ReadPixels to work correctly.  It would be preferable to have the
> driver handle all of that work.

A bit more prior art research:

GL_MESA_pack_invert - specifies this precisely for glReadPixels.

Your version of the spec needs more information. What does "flipped"
mean? Does it affect gl_FragCoord / gl_SamplePosition /
interpolateAtOffset? Does it affect the winding?

Might help to say that this is designed to undo the winsys flipping
relative to fbo rendering.

I'd also encourage you to write it such that this is also available on
desktop - no real reason to restrict this sort of thing to GLES.



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