SPRITE DISPLAY PRIORITIES

Sprites have the ability to cross each other's paths, as well as cross in front of, or behind other objects on the screen. This can give you a truly three dimensional effect for games.

Sprite to sprite priority is fixed. That means that sprite 0 has the highest priority, sprite 1 has the next priority, and so on, until we get to sprite 7, which has the lowest priority. In other words, if sprite 1 and sprite 6 are positioned so that they cross each other, sprite 1 will be in front of sprite 6.

So when you're planning which sprites will appear to be in the foreground of the picture, they must be assigned lower sprite numbers than those sprites you want to put towards the back of the scene. Those sprites will be given higher sprite numbers,

NOTE: A "window" effect is possible. If a sprite with higher priority has "holes" in it (areas where the dots are not set to 1 and thus turned ON), the sprite with the lower priority will show through. This also happens with sprite and background data.

Sprite to background priority is controllable by the SPRITE-BACKGROUND priority register located at 53275 ($D01B). Each sprite has a bit in this register. If that bit is 0, that sprite has a higher priority than the background on the screen. In other words, the sprite appears in front of background data. If that bit is a 1, that sprite has a lower priority than the background. Then the sprite appears behind the background data.

COLLISION DETECTS

One of the more interesting aspects of the VIC-II chip is its collision detection abilities. Collisions can be detected between sprites, or between sprites and background data. A collision occurs when a non-zero part of a sprite overlaps a non-zero portion of another sprite or characters on the screen.