There is the published OpenGL ES extension GL_OES_compressed_ETC1_RGB8_texture
for compressing RGB texture. But what's the extension for RGBA texture? From various
khronos web resource (cvs, document archive and wiki), I knwo there are 2 related
1:ETC3/ETC5, which use 128 bits to code 16 RGBA texels.
2:OES_compressed_iPACKMANalpha_texture, which uses 64 bits to code 16 RGBA texels.
It appears the 2nd extension is rather out-dated while the 1st one is more active
in the updating. I don't know which extension will finally be accepted as the formal
RGBA compression texture extension, just as the GL_OES_compressed_ETC1_RGB8_texture.
That is, which will be the upcoming GL_OES_compressed_ETC1_RGBA8_texture? Or
will we have the 3rd choice.
We really need to know the decision ASAP since we are developing an mobile GPU
supporting the RGBA texture compression.