3D Game Programming

Another way to handle moving between levels is to remove and create specific

game elements—like platforms and obstacles—while the rest of the scene

stays the same. As games get more complicated, this becomes a very hard

way to do it. But in this game we only have a few obstacles, so this approach

will work just fine.

Let’s build a Levels object to hold this information. This is a slightly different

reason to use objects than we saw in the previous chapter. There we used a

Ramp object to help us easily create multiple ramps. This time we build a Levels

object because it will be easier to think of it as a single thing.

Add the Levels code below the scoreboard code, but before the animate() function.

Create the Levels function constructor as follows so that it sets four properties:

functionLevels(scoreboard, scene) {

this.scoreboard = scoreboard;

this.scene = scene;

this.levels = [];

this.current_level = 0;

}

The Levels object will need to know about each of these things to do what it

needs to do. It needs access to the scoreboard to reset the counter between

levels. It needs access to the scene to draw and remove obstacles. It needs to

have a list of things on the different levels. Finally, it needs to know what the

current level is.

Objects Should Work on Only Their Own Properties

We don’t really need to pass the scoreboard and scene objects into our

constructor. Since all of our code is in the same place, it’s possible

for our Levels object to do something directly to the scoreboard variable.

Never do that.

There are two reasons. First, if we split all of this code into separate

JavaScript libraries, then scoreboard and scene won’t always be defined

in the library. Second, your code will be cleaner. Object-oriented

programming is not easy. Use whatever rules you can to keep it

from getting messy. This is a good rule.

With the constructor out of the way, let’s define the methods for the Levels

object. First, we need a way to add a new level:

Levels.prototype.addLevel =function(things_on_this_level) {

this.levels.push(things_on_this_level);

};

report erratum • discuss

Building Levels • 179

Prepared exclusively for Michael Powell