[Nouveau] [Bug 99033] [NV67] Incomplete implementation of OpenGL 2.1

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99033

--- Comment #6 from Ilia Mirkin <imirkin at alum.mit.edu> ---
(In reply to Ilya Indigo from comment #4)
> And determined the expansion are absent in nouveau, but there is nvidia.
> 
> GL_EXT_texture_format_BGRA8888
> GL_OES_mapbuffer
> GL_OES_texture_3D

These are ES extensions and not available in a desktop GL profile, on nvidia or
nouveau. They should, however, be present on a mesa ES profile. See
https://people.freedesktop.org/~imirkin/glxinfo/#p=es&v=Mesa%2010.6.0

> GL_ARB_framebuffer_object

Yeah, we don't support that one while NVIDIA does. It requires a lot of
work-arounding to handle all the cases not supported by the HW. Tripping those
up gets you off the fastpath in the blob driver and it slows down bigtime. We
have no such fallbacks in nouveau.

However GL_EXT_framebuffer_object is supported, and doesn't allow the
unsupportable conditions (like attachments of different sizes).

> Problem effect is "Taskbar thumbnail"
> ./kwin/effects/taskbarthumbnail/*
> 
> When you mouse hover over a tab on the taskbar instead of the window shows a
> blank thumbnail translucent rectangle of the appropriate size.
> When you switch on the OpenGL 1.2 kwin thumbnail is displayed.

That sounds like you're hitting a situation where you have a depth buffer
that's incompatible with the color buffer. We're supposed to fall back in that
situation, but don't. As a result, there's no depth, which can lead to no
rendering. Once this is supported, we could probably look at supporting
ARB_framebuffer_object, as similar mechanisms would be required.

Is there a link to the code I could glance at to see if that's likely the
issue?

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