Game Programming with the Simple DirectMedia Layer

The animation routine uses the dirty pixels technique so only a small portion of the screen is redrawn for each frame. With this technique, we keep track of the last position in which an object was drawn and the new position. When Bounce draws the Earth, first it erases the dirty pixels where it was by filling them with the background color, and then it draws the Earth in its new location. We fill rectangles and draw images using:

SDL_FillRect(screen, rectangle, color);
SDL_BlitSurface(image, NULL, screen, rectangle);

SDL_FillRect() fills a rectangle in an SDL_Surface, like the screen, with a color. The rectangle is specified using an SDL_Rect structure, and the color is created using SDL_MapRGB(). SDL_BlitSurface() copies a rectangle from one surface into a rectangle in another surface. If the source rectangle is NULL then the whole surface is copied. SDL_BlitSurface() is the routine that applies the color key and takes advantage of RLE encoding.

SDL reduces the time it takes to write games on Linux. It is small enough that learning it is a project, not a career, and it is powerful enough for commercial applications. I hope that between the information in this article and the source code for Bounce, you have learned enough of SDL to start modifying Bounce and building your own SDL games.

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