HTML5 Canvas, 2nd Edition

Simple Homegrown AI Overview

The enemy tanks chase the player object based on a set of simple rules. We have coded those rules into the gameStateEnemyMove() function, which is one of the longest and most complicated functions in this book. Let’s first step through the logic used to create the function, and then you can examine it in Example 9-2.

This function starts by looping through the enemy array. It must determine a new tile location on which to move each enemy. To do so, it follows some simple rules that determine the order in which the testBounds() function will test the movement directions:

1. First, it tests to see whether the player is closer to the enemy vertically or horizontally.

2. If vertically, and the player is above the enemy, it places up and then down in the directionsToTest array.

3. If vertically, and the player is below the enemy, it places down and then up in the directionsToTest array.

   Note

   The up and then down, or down and then up, directions are pushed into the directionsTest array to simplify the AI. The logic here is if the player is up from the enemy, but the enemy is blocked by an object, the enemy will try the opposite direction first. In our game, there will be no instance when an object blocks the direction the enemy tank wants to move in, because the only illegal direction is trying to move off the bounds of the screen. If we add tiles to our playfield that block the enemy, this entire set of AI code suddenly becomes very useful and necessary. We have included ...