[Mesa-dev] [Bug 96943] [gallium] glCopyPixels is affected by enabled texture state

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Fri Jul 15 18:48:10 UTC 2016


--- Comment #3 from Roland Scheidegger <sroland at vmware.com> ---
(In reply to Ilia Mirkin from comment #2)
> (In reply to Roland Scheidegger from comment #1)
> > The piglit test is probably wrong (I didn't really look), at least different
> > results based on enabled texturing don't surprise me. This is one of the
> > more weird "features" of glCopyPixels(), glDrawPixels() and friends.
> > From the respective man pages:
> > "Texture mapping, fog, and all the fragment operations are applied before
> > the fragments are written to the frame buffer." So if you don't disable
> > texturing, you'll get texturing on top of your copied pixels (which just
> > represent the primary color), in whatever way the shader specified (albeit
> > the texture coords should be constant IIRC).
> OK, so in that case, any time that a texture unit is enabled, we should be
> falling back to the drawpixels-style shader? (The multiply, btw, is coming
> from the texture combine logic, which defaults to "combine" aka "multiply".)

Technically I think yes. I don't know if the results are actually really
correct, though in any case (is it using the current tex coord etc.). And just
like this piglit test, I don't think any app ever expects this behavior - most
likely if they do this it's an app bug... So might just want to fix the piglit
test and pretend it's undefined behavior...

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