HTML 5 efficient drawing on canvas for game

I am attempting to develop a game with canvas element. Right now, I am drawing tiles (colored s开发者_StackOverflow中文版quares) as the background, and the hero controlled by arrow keys based off of this demo: http://www.lostdecadegames.com/demos/simple_canvas_game/

However, calling showDungeon() to draw my background makes the movement of the hero not smooth like in the demo. I think the problem is that I am drawing each tile as 32x32, which is making the movement slow in Chrome. Any suggestions or code optimizations I can do? The movement is fine when the tiles are 16x16, but I want the tiles 32x32. I kind of dont want to use CSS to double the size of the canvas as that can ruin the graphics with anti-aliasing. http://www.html5rocks.com/en/tutorials/casestudies/onslaught.html#toc-pixelated

// Draw everything
var render = function() {

   showDungeon();
    ctx.drawImage(img, hero.x, hero.y);

};

// The main game loop
var main = function() {
    var now = Date.now();
    var delta = now - then;

    update(delta / 1000);
    render();

    then = now;
};

// Let's play this game!
var then = Date.now();
setInterval(main, 1); // Execute as fast as possible

unrelated problem: for some reason, I couldnt draw a green square as a hero in render(), so i used an image instead. http://jsfiddle.net/4M5Xz/4/

---

You have a strange loop in the code:

function showDungeon() {
   for (var x = 0; x < (15*32); x++) {
      for (var y = 0; y < (15*32); y++) {
         ...
      }
   }
}

It's like you are drawing the background too many times. I changed it to:

function showDungeon() {
   for (var x = 0; x < 15; x++) {
      for (var y = 0; y < 15; y++) {
         ...
      }
   }
}

and it was smooth again.