Prevent requestAnimationFrame from running all the time

Question

I\'d like to know how to call the animate function through requestAnimationFrame only when it\'s realy needed. Currently the animate i

Answer 1

You need to implement a condition so you can break the loop, for example (adopt as needed):

var isRunning = true;

function loop() {

    ... funky stuff here ...

    /// test condition before looping
    if (isRunning) requestAnimationFrame(loop);
}

Now when you set isRunning to false the loop will break. For convenience it's recommended that you have a method to start and stop the loop:

function startLoop(state) {

    if (state && !isRunning) {
        isRunning = true;
        loop();             /// starts loop

    } else if (!state && isRunning) {
        isRunning = false;
    }
}

The condition can be set by anything you need it to be set by, for example on a callback after an animation has finished etc. The important part is that the condition flag is available to both scopes using it (ie. most commonly in the global scope).

UPDATE:

More specific in this case is that your condition (radius) will never reach the condition required to eventually stop the loop.

Here is what you can do to fix this:

DEMO

var isPlaying = false;

function animate(){
    /**
     * To make sure you will reach the condition required you need
     * to either make sure you have a fall-out for the steps or the
     * step will become 0 not adding/subtracting anything so your
     * checks below won't trigger. Here we can use a simple max of
     * the step and a static value to make sure the value is always > 0
    */
    if(mouseover){
        radius += Math.max( ((targetRadius-radius)/ease)*speed, 0.5);
    } else {
        radius -= Math.max( ((radius-baseRadius)/ease)*speed,   0.5);
    }

    /**
     * Now the checks will trigger properly and we can use the
     * isPlaying flag to stop the loop when targets are reached.
    */
    if(radius >= targetRadius) {
        radius = targetRadius;
        isPlaying = false;              /// stop loop after this
    } else if (radius <= baseRadius) {
        radius = baseRadius;
        isPlaying = false;              /// stop loop after this
    }
    
    drawDday(radius);

    /// loop?
    if (isPlaying === true) requestAnimationFrame(animate);
}

In order to trigger the loop we use a method that will check if the loop is running, if not it will reset the isPlaying flag and start the loop. We do this inside both mouseover and mouseout:

canvas.on('mouseover', function(e){
    mouseover = true;
    startAnim();

}).on('mouseout', function(){
    mouseover = false;
    startAnim();
});

The method is simply checking isPlaying and if not set it set it to true and starts the loop - this so that the loop is only started once:

function startAnim() {
    if (!isPlaying) {
        isPlaying = true;
        requestAnimationFrame(animate);
    }
}

In the demo I added console logging to show when the loop is running and when targets are hit.

Hope this helps.