JavaScript Canvas Animation

Question

This animation makes my fans spin up after several seconds, and it seems to have a sub-par framerate. I am trying to understand why, and optimize its performance.

Codepen

The animation function (this is the main part of the code):

function animate() {
    t++
    ctx.clearRect(0, 0, c.width, c.height);

    for (var i = 40; i < max; i+= 60) {
        var radius = Math.floor(i+Math.sin(t/10)*10)
        ctx.beginPath()
        ctx.arc(center[0], center[1], radius, 0, 2 * Math.PI, false)
        ctx.closePath()
        ctx.stroke()
    }

    requestAnimationFrame(animate)
}

The for loop draws the minimum number of circles needed in order to fill the screen. Their radius pulses in and out with a sine function based on the 't' variable.

Am I doing something wrong?

Answer 1

I guess I'm just assuming that it's inefficient because it makes my macbook's fans spin up after maybe 10 seconds

That's not really a good measure of "efficiency". The browser is trying to render 60 frames per second. That's a frame every ~16ms. Of course that's going to cause your processor to churn.

Math.floor(i+Math.sin(t/10)*10)

You can use <number> | 0 to trim off the decimal places of your numbers. In some JS engines and certain versions of JS engines, bitwise operations are faster than your regular math functions.

2 * Math.PI

There is a very small penalty when accessing object properties and becomes evident when you use it all over the place. Since Math.PI is a constant value, it wouldn't hurt if you assigned it to a variable for direct access. In fact, 2 * Math.PI is also constant. Why not put the result in a variable and spare the engine a multiplication operation as well.

function animate() {
  ...
  requestAnimationFrame(animate)
}

The issue with depending on just the render loop is the time it takes between updates. requestAnimationFrame can run faster or slower depending on conditions. If your "tweening" is time-sensitive, you might want to update based on delta-time instead.