nv::SlowCompressor::compressDXT1a error

[GoogleCodeExporter]

What steps will reproduce the problem?
1. try to convert as bc1a a texture with a black alpha channel (alpha=0)

What is the expected output? What do you see instead?
RGB channels shouldn't be influenced by alpha value.
RGB channels are multiplied by ALPHA.

What version of the product are you using? On what operating system?
last svn

Please provide any additional information below.
RGB channels of bc1a and bc3 should be the same

Original issue reported on code.google.com by marcoalt...@gmail.com on 9 Mar 2009 at 6:05

Attachments:

• bc1a.dds
• bc3.dds
• test.tga

[GoogleCodeExporter]

DXT1 is meant to be used with premultiplied alpha, there's no way around that. 
See
the Appendix "S3TC Compressed Texture Image Formats" in the S3TC OpenGL spec:

http://www.opengl.org/registry/specs/EXT/texture_compression_s3tc.txt

For a more detailed discussion, see:

http://home.comcast.net/~tom_forsyth/blog.wiki.html#[[Premultiplied%20alpha]]

Original comment by cast...@gmail.com on 9 Mar 2009 at 8:29

• Changed state: Invalid