I would like to update a region inside a PVRTC texture. I know that using glCompressedTexSubImage2D is not working on iOS, so what I tried to do is to update the texture data array manually, by simply copying over certain pixels from a different PVRTC texture. Now I do get strange results however (garbled data basically). Before I further try to debug this, is it even possible to do that (i.e. simply copying over the pixels from one image to a region in another image)?
PVRTC textures are twiddled (laid out in Morton order), so it is not possible to use the usual linear adressing to replace sub-parts of the textures. Furthermore as PVRTC regions are referencing neighbouring regions for the AB-color interpolation and modulation data you will have to incorporate padding around the texture part you are replacing.
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