[This was originally filed on Gentoo's bugzilla; at the request of Gentoo devs,
I'm taking this upstream for them.]

Using Gentoo's xorg-x11-6.8.0-r4 on a Matrox Millennium G450 card, 32 MB RAM.

Running the x11perf program, the antialiased trapezoid tests work correctly
under color depths > 8 bits (I tested 24 and 16 bits IIRC).  At 8 bits, these
things happen:

1. The test window that all the graphics operations are displayed in is created
a few pixels indented, both horizontally and vertically, from the upper left
corner of the screen.  Normally all tests should paint their graphics within the
provided window.  These tests, however, are offset up and to the left from where
they should be, so that they leak out of the window and onto the desktop.  The
graphics operations are being painted relative to the screen--not relative to
the window as they should be.

2. The performance is abysmal: Instead of a few hundred operations per second,
it can take up to several minutes to perform one operation, depending on the
test.  It's as if hardware acceleration isn't being used, and those X operations
are using (badly written) software routines.

Symptom 1 is easily manifest with the aatrap1 test.  Both symptoms are manifest
by running a range from aatrap1 to addatrapezoid300.

The ways to work around this problem are:
     o Change to a higher color depth
     o Use the VESA or fbdev drivers instead of "mga"
     o Turn off acceleration to make "mga" work
     o Set to "true" either (or both) of XaaNoScreenToScreenCopy or
XaaNoOffscreenPixmaps, to make accelerated "mga" work

Recompiling multiple times, I found no change by varying the MMX, SSE, or 3D-Now
related Gentoo USE flags.