html5 <canvas> framerate

Question

I was thinking of making a game using javascript for the game logic and the HTML5 canvas element to animate the drawing. My goal is to write something that works in browsers and on newer smartphones. So I wrote up a quick program that moves 100 circles around on the screen and shows me the frame rate. I was fairly disappointed with the results: Chrome: ~90 FPS Firefox: ~ 25 FPS iPhone: ~11 FPS

This was a pretty simple test so I don't like my chances when it comes to actually making a complete game. Is this the standard result from the canvas element or are there some tricks to make drawing faster, if you have any good links let me know? Is canvas just a toy at this point or can it be used for real world applications.

Edit Here's the code:

var ctx;
var width;
var height;
var delta;
var lastTime;
var frames;
var totalTime;
var updateTime;
var updateFrames;
var creats = new Array();

function init() {
    var canvas =document.getElementById('main');
    width = canvas.width;
    height = canvas.height; 
    ctx = canvas.getContext('2d');
    for(var i=0; i < 100; ++i) {
        addCreature();
    }
    lastTime = (new Date()).getTime();
    frames = 0;
    totalTime = 0;
    updateTime = 0;
    updateFrames =0;
    setInterval(update, 10);
}


function addCreature() {
    var c = new Creature(Math.random()*100,Math.random()*200);
    creats.push(c);
}

function update() {
    var now = (new Date()).getTime();
    delta = now-lastTime;
    lastTime = now;
    totalTime+=delta;
    frames++;
    updateTime+=delta;
    updateFrames++;
    if(updateTime > 1000) {
        document.getElementById('fps').innerHTML = "FPS AVG: " + (1000*frames/totalTime) + " CUR: " + (1000*updateFrames/updateTime);
        updateTime = 0;
        updateFrames =0;
    }

    for(var i=0; i < creats.length; ++i) {
        creats[i].move();
    }

    draw();
}

function draw() {
    ctx.clearRect(0,0,width,height);
    creats.forEach(drawCreat);
}

function drawCreat(c,i,a) {
    if (!onScreen(c)) {
        return;
    }
    ctx.fillStyle = "#00A308";
    ctx.beginPath();
    ctx.arc(c.x, c.y, 10, 0, Math.PI*2, true); 
    ctx.closePath();
    ctx.fill();
}

function onScreen(o) {
    return o.x >= 0 && o.y >= 0 && o.x <= width && o.y <=height;
}

function Creature(x1,y) {
    this.x = x1;
    this.y = y;

    this.dx = Math.random()*2;
    this.dy = Math.random()*2;

    this.move = function() {
        this.x+=this.dx;
        this.y+=this.dy;
        if(this.x < 0 || this.x > width) {
            this.dx*=-1;
        }
        if(this.y < 0 || this.y > height) {
            this.dy*=-1;
        }
    }

}

init();

Answer 1

Arcs are math-intensive to draw. You can dramatically improve performance by using drawImage or even putImageData instead of drawing the path each frame.

The image can be a file loaded from a URL or it can be an image created by drawing on a separate canvas not visible to the user (not connected to the DOM). Either way, you'll save a ton of processor time.