I spent the whole day trying to find out why glCompressedTexSubImage2D was returning INVALID_OPERATION when everything seemed to be fine.
I was working with FBOs & sub texture updates; so my guesses were:
- Offset X, Y, Width & Height weren't being aligned to multiples of 4. Nope. That was correct.
- My interpretation of GL_EXT_texture_compression_s3tc was incorrect and subimage was not possible with DXT textures.
- I was causing a buffer overflow/memory corruption. This didn't seem to be the case either.
- The calculation of the image data size was wrong.
- The PBO's size was wrong
- The PBO implementation was incorrect
- I even doubted a driver bug. I had to go to Riccio's compressed samples to see if they were working. They were.
- I checked if the Debug string extensions were enabled, they were. They were very quiet about the problem.
After 2 hours with CodeXL, I suddenly notice hwGamma in my code was true. Turns out, the GL buffer was being created with GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT5_EXT; but in glCompressedTexSubImage2D, the format being specified was GL_COMPRESSED_RGBA_S3TC_DXT5_EXT.
My suggestion is... pleaseeee!!! For the love of God, add Debug messages when supplying wrong parameters to glCompressedTexSubImage** family of functions. Diagnostics would include:
- Offsets/width/height don't meet the restrictions (i.e. SubImage is not supported for this format, the numbers aligned aligned to multiples of X, etc)
- The size parameter is no the one the driver expects (i.e. 131.072 bytes vs 131.073 bytes)
- The format paremeter doesn't match with the one the texture was created.
Tiny details like this would certainly help all developers and we will greatly appreciate, helping us to fix a problem that could be resolved in 2 minutes instead of wasting a whole day.
Simply an "INVALID_OPERATION" can be quite frustrating to deal with.
Just my feedback
Thanks in advance!