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[Public WebGL] ETC texture compression.



Texture compression is now rising to the top of my list of priorities...

I just got an email from Jacob Ström (at Ericsson) giving further
details of the ETC compression scheme - and a link to some useful papers
on the subject.   For anyone who is interested, I've added them as links
to the Wikipedia article on ETC compression:

     http://en.wikipedia.org/wiki/Ericsson_Texture_Compression

Anyway - a couple of highlights from Jacob's email that pretty much
confirm my intuition:

1) Jacob agrees that ETC1 isn't useful for compressing normal maps.
2) ETC1 can't compress RGBA maps, for that you need ETC2 - which isn't
finalized yet.
3) They believe that ETC1 quality is slightly better than S3TC (aka
DXT1) - but the artifacts are of a different nature and some test images
don't show an improvement. (Since the compression rates for ETC1 (6x)
are not as great as DXT1 (8x), that's about what you'd expect).

Anyway, on to my question...some graphics hardware (like my ancient 6800
card and my relatively new GeForce 285) don't support the OpenGL ETC1
extension.  Both of those nVidia cards have GL_ARB_texture_compression,
GL_EXT_texture_compression_s3tc and GL_NV_texture_compression_vtc - and
the 285 card has 'latc' and 'rgtc'...but neither support
GL_OES_compressed_ETC1_RGB8_texture - which is the ETC1 extension.  I
presume cellphones are much more likely to provide this support - but
evidently, it's far from universal.

So how will WebGL handle this on the desktop in practice?

  -- Steve

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