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[Octave-bug-tracker] [bug #44415] OpenGL plotted image has vertical line


From: Dan Sebald
Subject: [Octave-bug-tracker] [bug #44415] OpenGL plotted image has vertical line every 4096 pixels
Date: Tue, 31 Mar 2015 17:26:09 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:18.0) Gecko/20100101 Firefox/18.0 SeaMonkey/2.15

Follow-up Comment #22, bug #44415 (project octave):

What follows is a summary of the Mesa/OpenGL driver issue, and with this we
can close this bug and label it something appropriate.  Technically, I would
call it fixed or maybe in-progress, but it's in the hands of Mesa developers:

I've been able to compile Mesa and work with the drivers a bit.  (For details
on how to compile Mesa, send me an email.)  Exactly what driver everyone has
is hard to say, but from the comments below I gather several of us (probably
those with Nvidia hardware) end up with the swrast_dri.so driver--the fallback
when there isn't an accelerated Mesa driver specific to the video card--and I
point out that this is the legacy version of the driver, as there is now a new
Mesa driver in the works under a project called Gallium which also takes the
name of swrast_dri.so when it is compiled.

For reference, details are here:

https://bugs.freedesktop.org/show_bug.cgi?id=89586

The legacy swrast_dri.so driver is illustrated with some figures here:

https://bugs.freedesktop.org/attachment.cgi?id=114712

where one can see the vertical lines (positive scaling only) at the texture
width GL_MAX_TEXTURE_SIZE intervals just as
https://savannah.gnu.org/bugs/?44415#comment3 surmised.  A patched version of
the driver corrects this and is illustrated here:

https://bugs.freedesktop.org/attachment.cgi?id=114713

I don't know what the roadmap is for Mesa, but my guess is that over the years
Gallium swrast_dri.so will find more use in Linux distributions.  My
assessment is that Gallium is an improvement, but not without problems just
yet.  For example, that driver right now has a limit of GL_MAX_TEXTURE_SIZE
for an image, as shown here:

https://bugs.freedesktop.org/attachment.cgi?id=114714


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