SDL_GetRGB - Get RGB values from a pixel in the specified pixel format.
#include "SDL.h"
void SDL_GetRGB(Uint32 pixel,
SDL_PixelFormat *fmt, Uint8 *r, Uint8 *g, Uint8 *b);
Get RGB component values from a pixel stored in the specified pixel format.
This function uses the entire 8-bit [0..255] range when converting
color components from pixel formats with less than 8-bits per RGB component
(e.g., a completely white pixel in 16-bit RGB565 format would return [0xff,
0xff, 0xff] not [0xf8, 0xfc, 0xf8]).
SDL_GetRGBA, SDL_MapRGB,
SDL_MapRGBA, SDL_PixelFormat