Add option to preserve alpha test coverge for alpha channel mipmaps

[GoogleCodeExporter]

Alpha channel on mipmaps should be handled differently than color channels to 
preserve alpha test coverage: currently generated low-level mipmaps almost 
transparent if application use simple alpha test (texel_alpha < 
alpha_threshold).

Good description of this problem and available solutions presented here: 
http://the-witness.net/news/2010/09/computing-alpha-mipmaps/

Original issue reported on code.google.com by rutsky.v...@gmail.com on 13 May 2013 at 9:57

[GoogleCodeExporter]

I implemented described feature request, attaching patch against trunk version 
from Subversion.

Implementation similar to suggested in article [1], but it doesn't use 
subsampling. Patch tested with plain RGBA textures.

It performs well on my test textures. Also performance can be increased by 
using OpenMP.

[1] http://the-witness.net/news/2010/09/computing-alpha-mipmaps/

Original comment by rutsky.v...@gmail.com on 15 May 2013 at 3:56

Attachments:

• preserve_alpha_test_coverage.patch

[GoogleCodeExporter]

Sorry guys, haven't had much free time lately.  Thank you for the feature 
suggestion, and thank you Vladimir for the patch.  I will get it into trunk 
ASAP.

Original comment by ski...@gmail.com on 16 Jul 2013 at 8:14

• Changed state: Started

[GoogleCodeExporter]

Your changes are included in the new 3.0.0 release.  Thank you so much for your 
contribution Vladimir!

Original comment by ski...@gmail.com on 28 Nov 2013 at 7:25

• Changed state: Fixed