[osg-users] [osgPlugins] DDS textures not loading on Mac OSX and the latest trunk(3.5.0)

[Robert Osfield]

Hi Curtis,

I have gone through the DDS plugin checking the mipmap_offsets vector
that gets passed to the osg::Image to set where the mipmap levels are
and it all looks correct.  I've put debugging into the Texture.cpp
where the data gets download to the GPU and again all the values are
as they should be.

I have also modified the mipmap_offsets to produce invalid levels and
these errors get mapped onscreen as I would expect them to.  This
shows that these values are being used and are being used correctly.

I have also looked for OSX specifc code paths in Texture.cpp and the
only one relevant is the ClientStoreHint related code but as far as I
can tell this Hint shouldn't enabled in this case so it looks to me
exactly the same code paths should be used under Linux and OSX and
with exactly the same data.  The OSG code that I've looked at looks
fine, the data looks fine, it all seems to work as intended.

This leaves me without anything more that I can do at my end.  I'll
have to pass this on to OSX dev's to get to the bottom of why
precomputed compressed mipmaps don't work with OSX, they should, it's
a pretty well established part of the spec.

I can't rule out an OSG bug somewhere along the line, but at this
point I have say the most likely cause of the problem is OSX OpenGL
drivers. I would recommend looking into support forums to see if
others have had problems with precomputed compressed mipmaps.

As for workarounds for bugs drivers, perhaps the best thing to do in
this instance would be to look at disabling extensions, or having an
OSX specific hack in your own application code to disable the mipmaps
on the osg::Image so your OSX application doesn't attempt to pass
precomputed mipmaps.

Robert.