[Bug 34051] Low FPS with winemac driver in Unreal Tournament GOTY

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=34051

--- Comment #15 from Ken Thomases <ken at codeweavers.com> 2013-10-14 23:25:26 CDT ---
Actually, never mind.  I was able to reproduce the problem here.  I don't need
your glxinfo.

It turns out there's nothing wrong with the Mac driver.  The problem is the
implementation of GLX for Mac OS X in Mesa.  It's not rigorous.

GLX reports to the X11 driver that there are fbconfigs with 32 bits of depth
buffer.  Glxinfo shows that these fbconfigs are "slow" (i.e. software
rendered).  The X11 driver attempts to use such an fbconfig to satisfy
UT:GotY's request.

However, the code which enumerates the fbconfigs doesn't match the code which
actually sets up a GL context.  When setting up a GL context, GLX normally
refuses to allow the use of software rendering at all.  If you set the
environment variable LIBGL_ALLOW_SOFTWARE, it will at least allow it.

But even then it doesn't actually enforce the parameters of the requested
fbconfig.  For example, it passes along the request for 32 bits of depth
buffer, but it allows the OpenGL implementation to give it a pixel format which
has a smaller depth buffer if that would be "better".  If it insisted on a true
match, it would end up with software rendering.  But since it doesn't, the Mac
OpenGL picks an accelerated renderer.

So: X11 driver requested an unaccelerated fbconfig with 32 bits of depth
buffer.  GLX ends up using an accelerated pixel format with 24 bits of depth
buffer.


The Mac driver suffers by comparison because it actually respects and enforces
the pixel format selected by the app.  I guess, to get behavior similar to X11,
I will have to add a registry setting to the Mac driver to allow users to
forcibly disable the use of unaccelerated pixel formats, just like the patch
does.  Yeesh!

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