[Mesa3d-dev] Strange rendering using swrast?

[Matt S. <ma...@ki...>]

I'm trying to track something down we experienced trying to run
Blender over a plain software Mesa - we got some weird black
vertical stripes over the display at very regular and predictable
intervals.

After a few weeks of trials, tests and tweaks, I found a strange
occurance trying to find which part of Mesa was causing it. If
you modify init() in the GLUT gears demo so that it has:

	glEnable(GL_POLYGON_SMOOTH);
	glHint(GL_POLYGON_SMOOTH_HINT, GL_FASTEST);

(note, no blending, all it does is smudge the edges and run slow)

And then resize the window to be some 640x480 kind of size, there
is a hard black line down the middle of the window, and to the
right of that line, triangles "disappear" from the gears at
certain points.

If you size the window to 300x200 it doesn't seem to make any
difference. The gears are drawn normally. Incrementally sizing
it by 50 or so pixels at a time in both directions shows that
the "culling" only occurs after a certain horizontal distance
in the window, and always at the SAME horizontal distance,
regardless of window size (it seems to be about 400 pixels
here) which is why smaller windows aren't affected.

Can anyone reproduce this under Linux or so (software Mesa only)
and if so, can they explain it in terms of OpenGL standards (i.e.
am I doing something wrong here that causes this? Enabling the
polygon smooth functions shouldnt cause this kind of culling,
surely?)

This has been driving me mental for a few weeks now :)

-- 
Matt Sealey <ma...@ki...>