Bug#256729: xlibmesa-gl: Odd mouse cursor-related distortion in 3D apps.

[Chris Metzler <cmetzler@speakeasy.net>]

Package: xlibmesa-gl
Version: 4.3.0.dfsg.1-4
Severity: important

Hi.  This is being filed against xlibmesa-gl because it's 3D-specific;
but I'm too ignorant of the guts of X to know for a fact that that's
where it belongs.


System:  AMD Athlon XP 2000+, Asus A7V333 mobo (Via KT333 chipset),
        Matrox Millenium G550 video card.  I use the open source
        Matrox drivers that accompany the X packages; I do not use
        Matrox's proprietary mga_hal driver.  I also do not use
        gpm.


I recently upgraded X to the version currently in sarge
(4.3.0.dfsg.1-4).  Since then, in various 3D apps (e.g. blender,
flightgear, bzflag), I've been seeing some very odd behavior related
to the mouse cursor.

So long as the mouse is not moved, everything is fine.  However, if
the mouse cursor is moved, it flickers at high frequency.  Also, quite
often, a small rectangular off-colored patch appears at the location
where the mouse cursor started.  Typically, the color of that patch is
that of whatever background the application would be writing upon.  No
other distortion appears along the path the mouse moves, nor at the
mouse cursor's final destination.  Subsequent screen updates
(e.g. because of movement of the aircraft in flightgear) correct the
bogus region, so the distortion is transient.  However, in software
where the mouse gets moved a lot, or where the screen isn't being
continuously updated, this can make the screen extremely difficult to
read.

Unfortunately (because this is what I really need 3D graphics for),
this is especially a problem with blender.  One manipulates the mouse
small amounts quite a bit; the distorted area prevents you from seeing
the region on which you're working.  Using pulldown menus is also
difficult; patches of the blender work area background appear on top
of the menus, and the distortion makes menus difficult to impossible
to read.  See

http://www.speakeasy.net/~cmetzler/blender_distorted.png
http://www.speakeasy.net/~cmetzler/blender_distorted02.png

for relatively tame examples of mucked-up menus.

This behavior has occurred in every GL application I've checked which
uses the default X mouse cursor (the above, openuniverse, tuxracer
under the "Oliver's Math Class" course).  However, it does *not* occur
with several other 3D apps I tried (tuxracer, gl-117, criticalmass).
These apps are noteable in that they use a different (much larger)
mouse cursor; but I have no idea whether this correlation implies
anything significant.

I never saw this before updating my X installation to the version
currently in sarge (4.3.0.dfsg.1-4); I had been up to date with sarge
before this, so I had been running one of the "dfsg" versions of XF86,
but I'm not sure which that was (that is, which version was replaced
by 4.3.0.dfsg.1-4 in sarge).  I've looked through the Debian X11
changelog in /usr/share/doc/xlibmesa-gl, several versions back, and I
can't find anything that looks like a likely source for this problem
appearing, so I'm very confused.  But I'm happy to try anything you
might suggest to investigate this further.  Also, I should have an
Nvidia card available to me at the end of this week; perhaps switching
(and thus switching drivers/libGL/ etc.) and seeing what happens to
this effect will be informative.

Thanks for any help.

-c


-- System Information:
Debian Release: testing/unstable
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable')
Architecture: i386 (i686)
Kernel: Linux 2.4.23.040214a
Locale: LANG=C, LC_CTYPE=C

Versions of packages xlibmesa-gl depends on:
ii  libc6                     2.3.2.ds1-13   GNU C Library: Shared libraries an
ii  libxext6                  4.3.0.dfsg.1-4 X Window System miscellaneous exte
ii  xlibs                     4.3.0.dfsg.1-4 X Window System client libraries m

-- no debconf information