SDL2 - difference between RGB888 and RGB24

Question

As best I understand, both the RGB888 and RGB24 formats put their red components first, followed by green and then blue, and both formats take a total of 24 bits per pixel (because 8+8+8 = 24). Given this information both identifiers appear to describe the exact same format but I can verify that some of my code works with one of the two formats but not the other. What's the difference between the two that makes them incompatible?

Answer 1

They are different. If you look at SDL2/SDL_pixels.h you'll find:

SDL_PIXELFORMAT_RGB24 =
    SDL_DEFINE_PIXELFORMAT(SDL_PIXELTYPE_ARRAYU8, SDL_ARRAYORDER_RGB, 0,
                           24, 3)

SDL_PIXELFORMAT_RGB888 =
    SDL_DEFINE_PIXELFORMAT(SDL_PIXELTYPE_PACKED32, SDL_PACKEDORDER_XRGB,
                           SDL_PACKEDLAYOUT_8888, 24, 4)

SDL_PIXELFORMAT_RGBX8888 =
    SDL_DEFINE_PIXELFORMAT(SDL_PIXELTYPE_PACKED32, SDL_PACKEDORDER_RGBX,
                           SDL_PACKEDLAYOUT_8888, 24, 4)

So RGB24 is a tightly packed three byte format (RRGGBB), while RGB888 is a four byte format with the first byte going ignored (XXRRGGBB). So the format is just confusingly named and XRGB8888 would be a more appropriate name.

Don't know why they called it RGB888 instead of XRGB8888, but they leave the leading X away on other formats as well.