11: Isometric Tilemaps in Objective-C

Make ECC200 in Objective-C 11: Isometric Tilemaps

actions are run on the NPC and the directions need to be reversed, since you aren t moving the layer, the NPC is moving on the layer. As soon as you have NPCs wandering around, the next step is to ask how you can get them to move from A to B while avoiding obstacles and finding the shortest route. The answer to that is the A* pathfinding algorithm, which is an industry standard and has been adapted and tweaked for many situations. Tile-based games are ideal candidates for this particular pathfinding algorithm, since actor positions are usually restricted to the tile coordinates. For an in-depth introduction to the A* pathfinding algorithm, and honestly to a lot of game programming topics in general, you must visit Amit s A* pages at http://theory.stanford.edu/~amitp/GameProgramming/. And you ll want to visit Amit s Game Programming Information pages. He links to articles concerning artificial intelligence and tile-based games, including procedural world generation. A lot of the articles may seem dated but, in fact, most of them are timeless and are still valuable sources of information. Check them out at http://www-csstudents.stanford.edu/~amitp/gameprog.html.

In this chapter you ve learned what s special about isometric tilemaps, how isometric tiles are designed and how to create a tilemap with a perceived depth. You learned how to create and improve such an isometric tilemap with Tiled by adding an impassable border and preventing collisions. You also learned the techniques necessary to set up a tilemap for use with cocos2d, and how to setup cocos2d itself with 2D projection and a depth buffer for correct rendering of overlapping tiles and sprites. Finally, we added a player whose sprite is correctly clipped depending on whether it is in front or behind tiles. You can also move the player around tile by tile by tapping and holding the screen relative to the player sprite to make him go in that direction. That he will do unless the direction is blocked by a mountain, wall, or any other movementblocking tile that you set in Tiled. So far, we ve worked with games that needed to be controlled and animated in discrete steps. You were responsible for implementing all of the actor s movement and rotation as well as checking for collisions. In the next two chapters I ll introduce you to physics engines, which allow you to lean back as you watch your game s objects bounce around and collide with each other all by themselves. If this is the first time you ve worked with a physics engine, it will be a magical experience. Hold onto your hat!

Physics engines are what drive popular iOS games like Angry Birds, Stick Golf, Jelly Car, and Stair Dismount. They allow you to create a world that feels more dynamic and lifelike. Cocos2d is distributed with two physics engines: Box2D and Chipmunk. Both are designed to work only in two dimensions, so they re a perfect fit for cocos2d. In this chapter, you ll learn the basics of both physics engines, and along the way you ll probably come to appreciate one more than the other. I ll briefly explain the differences between the two physics engines, but for the most part it s a choice based on personal preference. If you ve never worked with a physics engine before, I ll also give you a quick introduction to their basic concepts and key elements.

A physics engine can be seen as an animation system for game objects. Of course, it s up to the game developer to connect and synchronize game objects like sprites with the physics objects, called rigid bodies. They are called that because physics engines animate them as if they were stiff, nondeformable objects. This simplification allows physics engines to calculate a large number of bodies. There are generally two types of bodies: dynamic (moving) and static (immovable) objects. The differentiation is important because static bodies never move and should never be moved and the physics engine can rely on certain optimizations based on the fact that static bodies never collide with each other. Dynamic bodies, on the other hand, collide with each other and with static bodies. They also have at least three defining parameters in addition to their position and rotation. One is density or mass in other words, a measure of how heavy an object is. Then there is friction how resistant or slippery the dynamic body is with respect to moving over surfaces. Finally, there is restitution, which determines the bounciness of the object. While impossible in the real world, physics engines can create dynamic bodies