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Under this mode, each 4x4 texel block can selectively use an alpha component or none. When alpha-enabled blocks are present, this is not reported in the DDPF_ALPHAPIXELS bit in the pixel format flags causing the reader-writer to report the file as a 3-components file (GL_COMPRESSED_RGB_S3TC_DXT1_EXT). The fix requires looking at each 4x4 texel block to detect the presence of 1-bit alpha encoding. When such a block is found, the internal & pixel formats are reported as GL_COMPRESSED_RGBA_S3TC_DXT1_EXT instead. See http://msdn.microsoft.com/library/default.asp?url=/library/en-us/directx9_c/Opaque_and_1_Bit_Alpha_Textures.asp for more information."
Welcome to the OpenSceneGraph (OSG).
For up to date information on the project, how to compile and run libraries
and examples, and see the documentation on the OpenSceneGraph website.
http://www.openscenegraph.org
Robert Osfield.
robert@openscenegraph.com
July 19th 2006.