Canvas Game Essentials - HTML5 Canvas - page 397

}
function canvasApp(){
var theCanvas = document.getElementById("canvas");
if (!theCanvas || !theCanvas.getContext) {
return;
}
var context = theCanvas.getContext("2d");
if (!context) {
return;
}
//canvasApp level variables
var rotation = 0;
var x = 50;
var y = 50;
var facingX = 0;
var facingY = 0;
var movingX = 0;
var movingY = 0;
var width = 20;
var height = 20;
var rotationalVelocity = 5; //how many degrees to turn the ship
var thrustAcceleration = .03;
var keyPressList = [];
function drawScreen() {
//check keys
if (keyPressList[38]==true){
//thrust
var angleInRadians = rotation * Math.PI / 180;
facingX = Math.cos(angleInRadians);
facingY = Math.sin(angleInRadians);
movingX = movingX+thrustAcceleration*facingX;
movingY = movingY+thrustAcceleration*facingY;
}
if (keyPressList[37]==true) {
//rotate counterclockwise
rotation −= rotationalVelocity;
}
if (keyPressList[39]==true) {
//rotate clockwise
rotation += rotationalVelocity;;
}