easing-fit

( refactoring attempts in dev branch )

Fit any easing function with keyframes and cubic-bezier timing function.

For example, assume we have an equation for a bouncing ball's height:

Math.abs(Math.sin(Math.pow(3 * t + 1.77, 2)) / ( Math.pow(3 * t + 2, 5 * t) + 1))

instead of simply sampling it with fixed interval of t, easing-fit breaks it into pieces of cubic bezier spline:

@keyframes bouncing {
  0% {
    animation-timing-function: cubic-bezier(0,0.5,1,0.6);
    transform: translate(0.4px);
  }
  11.5% {
    animation-timing-function: cubic-bezier(0.7,0.2,0.8,0.7);
    transform: translate(36.9px);
  }
  24.6% {
    animation-timing-function: cubic-bezier(0.2,0.3,0.3,0.9);
    transform: translate(0px);
  }
  32.3% {
    animation-timing-function: cubic-bezier(0.5,0.2,0.7,0.6);
    transform: translate(13.8px);
  }
  43.3% {
    animation-timing-function: cubic-bezier(0.3,0.5,0.6,0.8);
    transform: translate(0px);
  }
  49.6% {
    animation-timing-function: cubic-bezier(0.4,0.1,0.7,0.6);
    transform: translate(4px);
  }
  59.2% {
    animation-timing-function: cubic-bezier(0.3,0.5,0.7,0.8);
    transform: translate(0px);
  }
  64.6% {
    animation-timing-function: cubic-bezier(0.3,0.2,0.7,0.7);
    transform: translate(1.1px);
  }
  73.1% {
    animation-timing-function: cubic-bezier(0.3,0.5,0.7,1);
    transform: translate(0px);
  }
  100% {
    transform: translate(0px);
  }
}

Usage

First, import easing-fit and use it to create a keyframes object for our customized easing function:

easingFit = require("easing-fit");
customFunc = function(t) {
  return Math.sin(t * Math.PI * 2);
};
keyframes = easingFit.fit(customFunc, {});

The keyframes object contains all information needed. Then, convert it to CSS keyframe string with this help function:

var result = easingFit.toKeyframes(keyframes, {
  format: "css",
  prop: function(keyframe,config, idx) { return {"transform": "translate(" + keyframe.value + ")"}; },
  name: "sine",
  config: {.../* custom defined config */ }
});
/* result is the result CSS content */

Be sure to add your own prop function for converting value into CSS property. You can also check sample.ls for more detail.

Configuration

To tweak easing-fit further more, you can pass configuration into easingFit.fit, in the second parameter.

• SampleCount: how many points to sample in each segment. default is 1000.
• segSampleCount: how many points to sample when finding segment. default is 5.
• errorThreshold: pass to curve-fit, for error thresholding. default is 0.1
• precision: precision for output. default is 0.0001
• segPtrs: Array of points for forcing easing-fit to cut segments at. handy for approximating non-smooth function. default is [].

LICENSE

MIT