Maps the RGB 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 an alpha component it will be returned as all 1 bits (fully opaque).
A pixel value best approximating the given RGB 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).