On a Intel HD graphics Linux system with Mesa 10.1.3, I found that osg's Extensions::isTextureCompressionS3TCSupported() returned false, even though S3TC compressed textures *are* in fact working. I tested this by loading and rendering various DXT1, DXT3 and DXT5 compressed textures in the OSG.
"glxinfo | grep s3tc" gives:
GL_S3_s3tc
Note, if I install the package "libtxc-dxtn-s2tc0", I get in addition:
glxinfo | grep s3tc
GL_EXT_texture_compression_s3tc
GL_S3_s3tc
However, S3TC compressed textures worked correctly within the OSG even without libtxc-dxtn-s2tc0 installed.
I'm not sure what the differences between these extensions are, but based on the description at https://www.opengl.org/registry/specs/S3/s3tc.txt I would assume that both will work for OSG's purposes. The attached patch changes isTextureCompressionS3TCSupported() to accept either extension."
git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/branches/OpenSceneGraph-3.4@15034 16af8721-9629-0410-8352-f15c8da7e697