Bug#423739: libgl1-mesa-dri: banding in rendering when using blending for transparency

["Dan Torop" <dtorop934@gmail.com>]

Hi, Michael,

Thanks for the questions and information...  Responses follow:

This only happens with glBitmap().  I don't see it with either glDrawPixels
(GL_RGB or GL_RGBA format, with GL_UNSIGNED_BYTE data) or GL_QUADS (or
equivalent glRect).

I saw banding when I tried 6.5.2-4 Mesa with direct or indirect rendering, with
indirect rendering done via:

$ LIBGL_ALWAYS_INDIRECT=1 ./faded
freeglut (./faded): Unable to create direct context rendering for
window 'Blend test'
This may hurt performance.

But as you point out, DRI is loaded on X server startup in all those tests:

$ grep AIGLX /var/log/Xorg.0.log
(==) AIGLX enabled
(WW) AIGLX: 3D driver claims to not support visual 0x23
...snip...
(WW) AIGLX: 3D driver claims to not support visual 0x32
(II) AIGLX: Loaded and initialized /usr/lib/dri/r200_dri.so

If I disable DRI and restart the X server, then rerun the test program with or
without forced indirect rendering like so:

$ grep AIGLX /var/log/Xorg.0.log
(==) AIGLX enabled
(EE) AIGLX: DRI module not loaded
$ ./faded
freeglut (./faded): Unable to create direct context rendering for
window 'Blend test'
This may hurt performance.
$ LIBGL_ALWAYS_INDIRECT=1 ./faded
freeglut (./faded): Unable to create direct context rendering for
window 'Blend test'
This may hurt performance.

Then I see a very nice 50% gray screen and no banding in all the tests
against 6.5.2-4.

I should say that the personal incentive for filing this bug was the
change in DRI
blending behavior from 6.5.1-0.6 to 6.5.2-4, this is all in hopes of isolating
what happened...

Please let me know if there is anything else I could do to help isolate this?
I don't mind mucking around in code if it is of any use.

Thanks,

Dan


On 5/14/07, Michel Dänzer <daenzer@debian.org> wrote:
...
> Does this also happen when rendering say a GL_QUAD instead of using
> glBitmap?
...
> As indirect rendering seems to fail consistently (the xlib backend
> works completely differently), did you double-check that these cases
> were really using direct rendering?
...
> Note that when AIGLX is enabled (check Xorg.0.log), the Mesa *_dri.so
> driver will be used in both cases, though in contrast to direct
> rendering the X server will only load it once on X startup.
>
> > I'm reporting this against libgl1-mesa-dri, though perhaps it could
> > as easily be against libgl1-mesa-glx or the mesa source package?
>
> Or xserver-xorg-core...
...
> Can't reproduce it with the r300 driver from more or less up to date
> Mesa GIT here even with indirect rendering.