iPhone Game Development

Physics

In our game, physics will be a simple matter of entity-to-world and entity-to-entity collision in two dimensions. In Level 4, we have water tiles, but that will be a special case of entity-to-world.

Entities

What are “entities”? As we mentioned in Physics Engine, the game world consists of the “level,” the “player,” and the “animals.” To simplify things, we will say the game world consists of the “level” and “entities.” An entity is anything that exists in the game world within a particular level.

The player is an entity because she is in the world but can move around independently. The animals are also entities that can move around on their own. There can also be stationary entities, such as a button. Because a button has an animation and logic behind it (pressed and unpressed), it cannot be fully represented as merely a part of the tile-engine portion of the level; it must be an entity.

All entities need to have a position, a way to render themselves, and an update function that gets called every frame to allow their internal logic to progress.

We will begin by creating a class named Entity (which you already saw referenced in TileWorld):

//Entity.h @interface Entity : NSObject { CGPoint worldPos; CGPoint velocity; Sprite* sprite; TileWorld* world; } @property (nonatomic, retain) Sprite* sprite; @property (nonatomic) CGPoint position; - (id) initWithPos:(CGPoint) pos sprite:(Sprite*)sprite; - (void) drawAtPoint:(CGPoint) offset; - (void) update:(CGFloat) time; - (void) setWorld:(TileWorld*) ...