@lay:4401l4

Listing 4. Using a Colorkey Blit

#include <SDL/SDL.h>
#include <stdio.h>
#include <stdlib.h>

int main()
{
    SDL_Surface *screen;
    SDL_Surface *background;
    SDL_Surface *image;
    SDL_Rect src,dest;
    Uint32 colorkey;


    /* Same old initialization code, but go for a
       640x480 display instead of the previous
       256x256. */


    /* Load the bitmap files. */
    background = SDL_LoadBMP("background.bmp");
    if (background ==NULL) {
        printf("Unable to load bitmap.\n");
        return 1;
    };

    image = SDL_LoadBMP("tux.bmp");
    if (image == NULL) {
        printf("Unable to load bitmap.\n");
        return 1;
    };

    /* Draw the background. */
    src.x = 0; src.y = 0;
    src.w = background->w;
    src.h = background->h;
    dest.x = 0; dest.y = 0;
    dest.w = background->w;
    dest.h = background->h;
    SDL_BlitSurface(background,&src,screen,&dest);

    /* Draw the penguin without a colorkey. */
    src.x = 0;
    src.y = 0;
    src.w = image->w;
    src.h = image->h;
    dest.x = 30;
    dest.y = 90;
    dest.w = image->w;
    dest.h = image->h;
    SDL_BlitSurface(image,&src,screen,&dest);

    /* The penguin is stored on a blue background. We
       can use the SDL_MapRGB function to obtain the
       correct pixel value for pure blue. */
    colorkey = SDL_MapRGB(image->format,0,0,255);

    /* We'll now enable this surface's colorkey and draw
       it again. To turn off the colorkey again, we would
       replace the SDL_SRCCOLORKEY flag with zero. */
    SDL_SetColorKey(image,SDL_SRCCOLORKEY,colorkey);
    src.x = 0; src.y = 0;
    src.w = image->w;
    src.h = image->h;
    dest.x = screen->w - image->w - 30;
    dest.y = 90;
    dest.w = image->w; dest.h = image->h;
    SDL_BlitSurface(image,&src,screen,&dest);

    /* Ask SDL to update the entire screen. */
    SDL_UpdateRect(screen,0,0,0,0);

    /* Pause for a few seconds as the viewer gasps in awe. */
    SDL_Delay(10000);

    /* Free the memory that was allocated to the bitmaps. */
    SDL_FreeSurface(background);
    SDL_FreeSurface(image);

    return 0;
}