Mesa Can Do EXT_texture_compression_RGTC

[phoronix]

Phoronix: Mesa Can Do EXT_texture_compression_RGTC

In Mesa's quest to catch up to the proprietary Linux drivers (and the graphics drivers available under Windows), they are now a tiny bit closer. David Airlie has announced on the Mesa mailing list that he has implemented support for the EXT_texture_compression_RGTC extension into Mesa...

http://www.phoronix.com/vr.php?view=OTEzNA

[Laughing1]

Needs to be updated on this page: http://cgit.freedesktop.org/mesa/mesa/tree/docs/GL3.txt under GL 3.0.

[Azpegath]

Hey, at least we recently moved up to 2.1 instead of 1.4...

[smitty3268]

I believe S3TC is DXT3, and these are DXT4 and 5.

Does anyone know what they're used by? Does this help WINE apps?

[Xipeos]

I believe S3TC is DXT3, and these are DXT4 and 5.

Does anyone know what they're used by? Does this help WINE apps?

All DXT compressions are "S3TC". RGTC was designed for compressing normal maps, and can replace DXT5.

[Xipeos]

Correction: it can replace DirectX's 3Dc/BC5 (which is better than DXT5).

[LiquidAcid]

Totally wrong, RGTC is red+green block texture compression. S3TC is RGB and RGBA block compression. How is BC5 (which is a RG compression formats) supposed to replace DXT5 (which is a RGBA compression format) if BC5 can only handle two color channels?!

[Xipeos]

Totally wrong, RGTC is red+green block texture compression. S3TC is RGB and RGBA block compression. How is BC5 (which is a RG compression formats) supposed to replace DXT5 (which is a RGBA compression format) if BC5 can only handle two color channels?!

Better for normal maps. Based that claim on the research presented in my second link:

[3Dc] produces much better quality than DXT1 or DXT5 normal map compression.
(...)
The [3Dc] format can be loaded in OpenGL as LATC or RGTC.

[LiquidAcid]

Your statement is still wrong though. An RG format can never replace an RGB/RGBA format. Using DXTn formats for normal compression was always kind of a hack.

[LiquidAcid]

Addition to last post:
The very nVidia article you quote explains why using DXTn for encoding normal/tangent data is a hack.
If anything, then texture_RG and texture_RGTC are the proper ways to store such information.