OpenGL texture upload: UNSIGNED_BYTE vs UNSIGNED_INT_8_8_8_8

Question

I'm calling glTexSubImage2D. If my pixel format is GL_RGBA, then are the pixel types GL_UNSIGNED_BYTE and GL_UNSIGNED_INT_8_8_8_8 fully equivalent?

Also, are these two pairs equivalent?

• Format = GL_RGBA, Type = GL_UNSIGNED_INT_8_8_8_8
• Format = GL_BGRA, Type = GL_UNSIGNED_INT_8_8_8_8_REV

I've tried reading the OpenGL spec and the GL_EXT_packed_pixels spec, but honestly I can't make head or tail of them.

Answer 1

The answers are No and No. You have to think about the byte order in your computer. If you have GL_RGBA and GL_UNSIGNED_INT_8_8_8_8, that means that pixels are stored in 32-bit integers, and the colors are in the logical order RGBA in such an integer, e.g. the red is in the high-order byte and the alpha is in the low-order byte. But if the machine is little-endian (as with Intel CPUs), it follows that the actual order in memory is ABGR. Whereas, GL_RGBA with GL_UNSIGNED_BYTE will store the bytes in RGBA order regardless whether the computer is little-endian or big-endian.

GL_BGRA with GL_UNSIGNED_INT_8_8_8_8_REV would store colors in an integer in the logical order ARGB, but then on a little-endian machine, you get BGRA order in memory.