Additive Animation

This is a simple npm module which implements additive animation algorithm described here:

http://iosoteric.com/additive-animations-animatewithduration-in-ios-8/

or in this video:

https://developer.apple.com/videos/wwdc/2014/#236

It combines concurrent animations of the same object into one smooth continuous animation.

Demo

Here it is (I hope you like cats).

Usage Example

Let's make smooth scrolling for window. Create animation object and provide the options. You need to provide at least onRender callback:

var AdditiveAnimation = require('additive-animation');

function onRender(state) {
  window.scrollTo(0, state.y);
};

var animation = new AdditiveAnimation({
  onRender: onRender
});

Now call animate method to start animation:

var fromState = { y: 0 };
var toState = { y: 1000 };
var duration = 1000;

animation.animate(fromState, toState, duration);

To add new animation with another final state, just call it again:

fromState = { y: window.scrollTop };
toState = { y: 2000 };

animation.animate(fromState, toState, duration);

API

animation = new AdditiveAnimation(options)

Creates animation object. Possible options:

Name | Signature | Description :---------|:--------|:-------- onRender | function(state) | (required) a callback for rendering current animation state. onFinish | function(finalState) | Fires after the last animation is completed. onCancel | function() | Fires if animation is canceled. enabledRAF | bool | Use window.requestAnimationFrame in animation loop. True by default. Note: if you use it, you should probably also use some polyfill, like this: https://github.com/cagosta/requestAnimationFrame fps | number | If RAF is disabled, setTimeout is used in animation loop. Here you can define frequency (60 frames per second by default).

animation.animate(fromState, toState, duration, easing)

Animates object state. fromState and toState are expected to be the objects with number values, e.g. { x: 100, y: 200 }. duration is animation duration in milliseconds.

easing is a function used for easing. It could be a string (name of one of the functions described here: https://gist.github.com/gre/1650294 - for example, 'linear' or 'easeInOutQuad') or your own function (assuming it's input and output values are in range [0, 1]). 'easeInOutQuad' by default.

animation.isAnimating()

Returns true if there is an active animation.

animation.cancel()

Cancels current animation.