Canvas Games: Part I - HTML5 Canvas - page 683

Rock size constants
These variables set up some human-readable values for the three rock sizes, allowing us
to simply use the constant instead ofa literal value. We can then change the literal value if
needed:

const const ROCK_SCALE_LARGE = 1 ;

const

const ROCK_SCALE_MEDIUM = 2 ;
const const ROCK_SCALE_SMALL = 3 ;

Logical display objects
These variables set up the single player object and arrays to hold the various other logical
display objects for our game. See the upcoming sections The Player Object and Arrays of
Logical Display Objects for further details about each:

var var player = {};

var

var rocks = [];
var var saucers = [];

var

var playerMissiles = [];
var var particles = []

var var saucerMissiles = [];

Level-specific variables

The level-specific variables handle the difficulty settings when the game level increases.
See the section Level Knobs for more details about how these are used:

var var levelRockMaxSpeedAdjust = 1 ;

var var levelSaucerMax = 1 ;

var

var levelSaucerOccurrenceRate = 25
var var levelSaucerSpeed = 1 ;

var var levelSaucerFireDelay = 300 ;

var

var levelSaucerFireRate = 30 ;
var

var levelSaucerMissileSpeed = 1 ;