HTML5 Canvas - Wheel spinning function acts strange

Question

In HTML5 canvas, I have a wheel, that I'm trying to spin, however the wheel is acting really crazy. It's being swung around the screen, out of it and into it again.

var canvas = document.getElementById("my-canvas");
var ctx = canvas.getContext("2d");

var img = new Image();
img.src = "http://www.roulette30.com/wp-content/uploads/americanroulette.png";

ctx.drawImage(img, 70, 70, 200, 200);

function spinWheel() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
    ctx.translate(0, 0, canvas.width, canvas.height);
    ctx.rotate(1 * Math.PI / 180);
    ctx.drawImage(img, 70, 70, 200, 200);
}

setInterval(spinWheel, 0);

#my-canvas {
  border: 1px solid black;
}

<!--<img id="my-image" height="200" width="200" src="http://www.roulette30.com/wp-content/uploads/americanroulette.png">
-->
<canvas id="my-canvas" width="400" height="400"></canvas>

I was certain that if I called the translate method, I could always have the wheel positioned in the center of the screen. Along with rotate, this was sure to work.

Any insights will be welcomed.

Answer 1

You need to translate outside of your spin code, to half width/height for dead center.

var canvas = document.getElementById("my-canvas");
var ctx = canvas.getContext("2d");

var img = new Image();
img.src = "http://www.roulette30.com/wp-content/uploads/americanroulette.png";

var speed = 1; // adding increases speed
var loop = true;

ctx.translate(canvas.width/2, canvas.height/2);

function spinWheel() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  ctx.rotate(speed * Math.PI / 180);
  ctx.drawImage(img, -(img.width/2), -(img.height/2));
  if (loop) requestAnimationFrame(spinWheel);
}

spinWheel();

#my-canvas {
  border: 1px solid black;
}

<canvas id="my-canvas" width="400" height="400"></canvas>