Flywheel

Flywheel is a lightweight tool to make working with HTML5's requestAnimationFrame simpler.

API

Setting up a loop

Flywheel takes two arguments:

• A callback to loop over. It passes the amount of time passed since the last frame to the callback.

• A DOM element, which acts identically to the requestAnimationFrame second parameter.

After setup, it returns an object that can be used to manipulate the loop. By default, the loop is not running; to start it, use the methods from the next section.

    
    var element = document.getElementsByTagName("canvas")[0]

    function animation_loop(time_delta){
        /* do animation work here */
    }

    var fw = flywheel(animation_loop, element)

Starting, stopping and toggling a loop

    
    // start and stop 
    fw.start()
    fw.stop()

    // toggle loop on and off
    fw.toggle()
    fw.toggle()

Changing the callback and element

To change a callback:

    fw.callback = function(time_delta){
        /* do alternative animation work here */
    }

To change an element:

    fw.element = document.getElementById("my_other_canvas")

Time Delta capping:

When a page loses focus or the loop is paused, the gap between frames can be large enough to cause problems in games (especially where acceleration or collision detection is involved). To combat this, flywheel limits the time_delta value passed to the callback ( by default, to 50ms; equivilent to ~20fps ).

To change the cap:

    fw.framerate_cap = 40

Step for debugging:

    // step forwards a frame (assuming a time delta of 16ms; equivilent to ~60fps)
    fw.step()

    // step forwards with a custom time delta.
    fw.step(30)

Testing

Feel free to run the test suite

Licensing

This software is available under the MIT license.