Video is probably the most common thing that SDL is used for, and +so it has the most complete subsystem. Here are a few +examples to demonstrate the basics.
This is what almost all SDL programs have to do in one way or +another.
Example 2-1. Initializing the Video Display
SDL_Surface *screen;
+
+ /* Initialize the SDL library */
+ if( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
+ fprintf(stderr,
+ "Couldn't initialize SDL: %s\n", SDL_GetError());
+ exit(1);
+ }
+
+ /* Clean up on exit */
+ atexit(SDL_Quit);
+
+ /*
+ * Initialize the display in a 640x480 8-bit palettized mode,
+ * requesting a software surface
+ */
+ screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE);
+ if ( screen == NULL ) {
+ fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
+ SDL_GetError());
+ exit(1);
+ }If you have a preference for a certain pixel depth but will accept any +other, use SDL_SetVideoMode with SDL_ANYFORMAT as below. You can also +use SDL_VideoModeOK() to find the native video mode that is closest to +the mode you request.
Example 2-2. Initializing the Best Video Mode
/* Have a preference for 8-bit, but accept any depth */
+ screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE|SDL_ANYFORMAT);
+ if ( screen == NULL ) {
+ fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
+ SDL_GetError());
+ exit(1);
+ }
+ printf("Set 640x480 at %d bits-per-pixel mode\n",
+ screen->format->BitsPerPixel);The following function loads and displays a BMP file given as +argument, once SDL is initialised and a video mode has been set.
Example 2-3. Loading and Displaying a BMP File
void display_bmp(char *file_name)
+{
+ SDL_Surface *image;
+
+ /* Load the BMP file into a surface */
+ image = SDL_LoadBMP(file_name);
+ if (image == NULL) {
+ fprintf(stderr, "Couldn't load %s: %s\n", file_name, SDL_GetError());
+ return;
+ }
+
+ /*
+ * Palettized screen modes will have a default palette (a standard
+ * 8*8*4 colour cube), but if the image is palettized as well we can
+ * use that palette for a nicer colour matching
+ */
+ if (image->format->palette && screen->format->palette) {
+ SDL_SetColors(screen, image->format->palette->colors, 0,
+ image->format->palette->ncolors);
+ }
+
+ /* Blit onto the screen surface */
+ if(SDL_BlitSurface(image, NULL, screen, NULL) < 0)
+ fprintf(stderr, "BlitSurface error: %s\n", SDL_GetError());
+
+ SDL_UpdateRect(screen, 0, 0, image->w, image->h);
+
+ /* Free the allocated BMP surface */
+ SDL_FreeSurface(image);
+}The following two functions can be used to get and set single +pixels of a surface. They are carefully written to work with any depth +currently supported by SDL. Remember to lock the surface before +calling them, and to unlock it before calling any other SDL +functions.
To convert between pixel values and their red, green, blue +components, use SDL_GetRGB() and SDL_MapRGB().
Example 2-4. getpixel()
/*
+ * Return the pixel value at (x, y)
+ * NOTE: The surface must be locked before calling this!
+ */
+Uint32 getpixel(SDL_Surface *surface, int x, int y)
+{
+ int bpp = surface->format->BytesPerPixel;
+ /* Here p is the address to the pixel we want to retrieve */
+ Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;
+
+ switch(bpp) {
+ case 1:
+ return *p;
+
+ case 2:
+ return *(Uint16 *)p;
+
+ case 3:
+ if(SDL_BYTEORDER == SDL_BIG_ENDIAN)
+ return p[0] << 16 | p[1] << 8 | p[2];
+ else
+ return p[0] | p[1] << 8 | p[2] << 16;
+
+ case 4:
+ return *(Uint32 *)p;
+
+ default:
+ return 0; /* shouldn't happen, but avoids warnings */
+ }
+}Example 2-5. putpixel()
/*
+ * Set the pixel at (x, y) to the given value
+ * NOTE: The surface must be locked before calling this!
+ */
+void putpixel(SDL_Surface *surface, int x, int y, Uint32 pixel)
+{
+ int bpp = surface->format->BytesPerPixel;
+ /* Here p is the address to the pixel we want to set */
+ Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;
+
+ switch(bpp) {
+ case 1:
+ *p = pixel;
+ break;
+
+ case 2:
+ *(Uint16 *)p = pixel;
+ break;
+
+ case 3:
+ if(SDL_BYTEORDER == SDL_BIG_ENDIAN) {
+ p[0] = (pixel >> 16) & 0xff;
+ p[1] = (pixel >> 8) & 0xff;
+ p[2] = pixel & 0xff;
+ } else {
+ p[0] = pixel & 0xff;
+ p[1] = (pixel >> 8) & 0xff;
+ p[2] = (pixel >> 16) & 0xff;
+ }
+ break;
+
+ case 4:
+ *(Uint32 *)p = pixel;
+ break;
+ }
+}The following code uses the putpixel() function above to set a +yellow pixel in the middle of the screen.
Example 2-6. Using putpixel()
/* Code to set a yellow pixel at the center of the screen */
+
+ int x, y;
+ Uint32 yellow;
+
+ /* Map the color yellow to this display (R=0xff, G=0xFF, B=0x00)
+ Note: If the display is palettized, you must set the palette first.
+ */
+ yellow = SDL_MapRGB(screen->format, 0xff, 0xff, 0x00);
+
+ x = screen->w / 2;
+ y = screen->h / 2;
+
+ /* Lock the screen for direct access to the pixels */
+ if ( SDL_MUSTLOCK(screen) ) {
+ if ( SDL_LockSurface(screen) < 0 ) {
+ fprintf(stderr, "Can't lock screen: %s\n", SDL_GetError());
+ return;
+ }
+ }
+
+ putpixel(screen, x, y, yellow);
+
+ if ( SDL_MUSTLOCK(screen) ) {
+ SDL_UnlockSurface(screen);
+ }
+ /* Update just the part of the display that we've changed */
+ SDL_UpdateRect(screen, x, y, 1, 1);
+
+ return;