3D Game Programming

functionremoveItems() {

game_items.forEach(function(item) {

scene.remove(item);

});

game_items = [];

}

Adding items to the river is where things start to get interesting. The ground

still has the river_points property. We’ll use that list of points to randomly place

power-up fruit at a couple of places along the river. Randomly placing the fruit

will make each new game a different challenge for players.

Only we don’t want to be quite random about it. If it were completely random,

we might end up with two pieces of fruit in the same place or one right at the

start.

Recall that there are 100 faces in the ground and 100 points in the ground

that we are using to describe the middle of the river. Lets randomly place a

power-up fruit around river point 20 and another around point 70. The fol-

lowing will do what we need:

functionaddItems(ground, scoreboard) {

varpoints = ground.river_points;

varrandom20 = Math.floor(20 + 10*Math.random()),

fruit20 = addFruitPowerUp(points[random20], ground, scoreboard);

game_items.push(fruit20);

varrandom70 = Math.floor(70 + 10*Math.random()),

fruit70 = addFruitPowerUp(points[random70], ground, scoreboard);

game_items.push(fruit70);

}

The main purpose of this code block is to call the addFruitPowerUp() function that

we’ll build shortly. The fruit20 and fruit70 items are then pushed onto the list

of all game items (so that they can later be removed as needed).

The random20 and random70 numbers might look a little complicated at first,

but if you look closely, they ought to make some sense. Let’s look at just ran-

dom20 to better understand. The Math.random() function generates a number

between 0 and 1.

• If Math.random() is 0 , then 10Math.random() is 0 , making 20 + 10Math.random()
  end up as 20.


• If Math.random() is 0.5, then 10Math.random() is 5 , making 20 + 10Math.random()
  end up as 25.

report erratum • discuss

Setting the Finish Line • 203

Prepared exclusively for Michael Powell