Maps the RGBA color value to the specified pixel format and returns the pixel value as a 32-bit int.
If the format has a palette (8-bit) the index of the closest matching color in the palette will be returned.
If the specified pixel format has no alpha component the alpha value will be ignored (as it will be in formats with a palette).
A pixel value best approximating the given RGBA color value for a given pixel format. If the pixel format bpp (color depth) is less than 32-bpp then the unused upper bits of the return value can safely be ignored (e.g., with a 16-bpp format the return value can be assigned to a Uint16, and similarly a Uint8 for an 8-bpp format).