Pixel Perfect Collision Detection

Sloppy collisions are boring. This library extends AndEngine's Sprite and AnimatedSprite with pixel-perfect collision detection.

Note: this will only work for collisions between unrotated, unscaled sprites.

Installation

• Save the jar file to your project's libs directory.
• If you are using eclipse, right-click on the jar, and click on build path > Add To Build Path
• Done!

Usage

PixelPerfectSprites work just like regular sprites, but are initialized with PixelPerfectTextureRegions, which are created by the PixelPerfectTextureRegionFactory.

Your code should look something like this:

public class Game extends BaseGameActivity{
    private Texture texture;
    private PixelPerfectTextureRegion diamondRegion;
    private PixelPerfectTiledTextureRegion triangleRegion;
    ...

    public void onLoadResources(){
        PixelPerfectTextureRegionFactory.setAssetBasePath("gfx/");
        ...
      
        texture = new Texture(256, 64, TextureOptions.NEAREST_PREMULTIPLYALPHA);
        diamondRegion = PixelPerfectTextureRegionFactory.createFromAsset(texture, this, "diamond.png", 0,0);
        triangleRegion = PixelPerfectTextureRegionFactory.createTiledFromAsset(texture, this, "triangle.png", 65,0);

        getEngine().getTextureManager().loadTextures(texture, ...);
    }
     
    public void onLoadScene(){
        ...
        PixelPerfectSprite diamond = new PixelPerfectSprite(0,0,ppRegion);
        scene.getTopLayer().addEntity(diamond); 

        PixelPerfectSprite spinningTriangle = new PixelPerfectSprite(100,100,ppRegion);
        spinningTriangle.animate(20, true);
        scene.getTopLayer().addEntity(spinningTriangle); 

        spinningTriangle.collidesWith(diamond);
    }
} 

For a more complete example, check out the demo

Technical Notes

The alpha channel of each sprite's bitmap is packed into a 1-bit-per-pixel int[][] mask. If the bounding boxes of the sprites intersect, logical shifts and &'s are used to test the intersection for a pixel-level collision.

The running time of the collision algorithm is proportional to the area of the intersection of the bounding boxes of the sprites being tested. 1000 collision checks against a 100x100 pixel intersection ran in 200ms on my HTC Incredible. At that rate, it shouldn't be any sort of bottleneck in your game. However, my benchmark was crude and my game required only a fraction of that speed, so YMMV.

Contact

If you have any questions, or find any bugs, let me know.

[email protected]