I think it is a little weird to use DXT1 with --RGBA-compressed (so 1bit
alpha as you said), and to use DXT3 with --compressed (double the size
of the texture to handle alpha channel). Now we will see what Robert
thinks about it :)
Fabien
________________________________
From: [email protected]
[mailto:[email protected]] On Behalf Of
Christiansen, Brad
Sent: lundi 11 octobre 2010 10:31
To: OpenSceneGraph Submissions
Subject: Re: [osg-submissions] [vpb] Bug fix with NVTT
Hi,
I am not 100% sure it was an error to use DXT1 for RGBA. The code on
line 260 of TextureUtils.cpp setups up handling of RGBA textures using
nvtt
;;Format_DXT1a.
>From my reading, you can use DXT1 with an alpha channel but the alpha is
only a 1 bit value. This might not work in many cases but I would guess
that alpha is used in output textures from VPB mostly for textures on
the boundary of the source data where only some of the texture contains
data (if that makes sense). That is certainly how my terrains use alpha
and I would like to use this option (DTX1a for my output of RGBA
textures).
Another quick question: if --RGBA-compressed (OpenGL compression) is
passed to osgdem / vpbmaster, what format will the nvtt code path use?
Is this simply not supported? That is my reading of the source.
Cheers,
Brad
ps- I am testing your changes now. Thanks again.
From: [email protected]
[mailto:[email protected]] On Behalf Of
Fabien Lavignotte
Sent: Monday, 11 October 2010 4:07 PM
To: [email protected]
Subject: [osg-submissions] [vpb] Bug fix with NVTT
Hi Robert,
As seen by Brad, the code with nvtt does not works correctly when using
--terrain.
So here is the fix in TextureUtils.cpp.
I also swapped the compression used with
BuildOptions::COMPRESSED_TEXTURE and
BuildOptions::COMPRESSED_RGBA_TEXTURE.
It dit not seems correct to use DXT1 for RGBA, i think it was just a
copy/paste error.
Cheers,
Fabien
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