3D Basics - HTML5 Animation with JavaScript - page 341

friction = 0.98,
fl = 250,
vpX = canvas.width / 2,
vpY = canvas.height / 2;
window.addEventListener('keydown', function (event) {
switch (event.keyCode) {
case 38: //up
vy -= 1;
break;
case 40: //down
vy += 1;
break;
case 37: //left
vx -= 1;
break;
case 39: //right
vx += 1;
break;
case 16: //shift
vz += 1;
break;
case 17: //control
vz -= 1;
break;
}
}, false);
(function drawFrame () {
window.requestAnimationFrame(drawFrame, canvas);
context.clearRect(0, 0, canvas.width, canvas.height);
xpos += vx;
ypos += vy;
zpos += vz;
vx *= friction;
vy *= friction;
vz *= friction;
if (zpos > -fl) {
var scale = fl / (fl + zpos);
ball.scaleX = ball.scaleY = scale;
ball.x = vpX + xpos * scale;
ball.y = vpY + ypos * scale;
ball.visible = true;
} else {
ball.visible = false;
}
if (ball.visible) {
ball.draw(context);
}
}());