amator/index.js

Tiny animation library

var BezierEasing = require('bezier-easing')

// Predefined set of animations. Similar to CSS easing functions
var animations = {
  ease:  BezierEasing(0.25, 0.1, 0.25, 1),
  easeIn: BezierEasing(0.42, 0, 1, 1),
  easeOut: BezierEasing(0, 0, 0.58, 1),
  easeInOut: BezierEasing(0.42, 0, 0.58, 1),
  linear: BezierEasing(0, 0, 1, 1)
}


module.exports = animate;
module.exports.makeAggregateRaf = makeAggregateRaf;
module.exports.sharedScheduler = makeAggregateRaf();


function animate(source, target, options) {
  var start = Object.create(null)
  var diff = Object.create(null)
  options = options || {}
  // We let clients specify their own easing function
  var easing = (typeof options.easing === 'function') ? options.easing : animations[options.easing]

  // if nothing is specified, default to ease (similar to CSS animations)
  if (!easing) {
    if (options.easing) {
      console.warn('Unknown easing function in amator: ' + options.easing);
    }
    easing = animations.ease
  }

  var step = typeof options.step === 'function' ? options.step : noop
  var done = typeof options.done === 'function' ? options.done : noop

  var scheduler = getScheduler(options.scheduler)

  var keys = Object.keys(target)
  keys.forEach(function(key) {
    start[key] = source[key]
    diff[key] = target[key] - source[key]
  })

  var durationInMs = typeof options.duration === 'number' ? options.duration : 400
  var durationInFrames = Math.max(1, durationInMs * 0.06) // 0.06 because 60 frames pers 1,000 ms
  var previousAnimationId
  var frame = 0

  previousAnimationId = scheduler.next(loop)

  return {
    cancel: cancel
  }

  function cancel() {
    scheduler.cancel(previousAnimationId)
    previousAnimationId = 0
  }

  function loop() {
    var t = easing(frame/durationInFrames)
    frame += 1
    setValues(t)
    if (frame <= durationInFrames) {
      previousAnimationId = scheduler.next(loop)
      step(source)
    } else {
      previousAnimationId = 0
      setTimeout(function() { done(source) }, 0)
    }
  }

  function setValues(t) {
    keys.forEach(function(key) {
      source[key] = diff[key] * t + start[key]
    })
  }
}

function noop() { }

function getScheduler(scheduler) {
  if (!scheduler) {
    var canRaf = typeof window !== 'undefined' && window.requestAnimationFrame
    return canRaf ? rafScheduler() : timeoutScheduler()
  }
  if (typeof scheduler.next !== 'function') throw new Error('Scheduler is supposed to have next(cb) function')
  if (typeof scheduler.cancel !== 'function') throw new Error('Scheduler is supposed to have cancel(handle) function')

  return scheduler
}

function rafScheduler() {
  return {
    next: window.requestAnimationFrame.bind(window),
    cancel: window.cancelAnimationFrame.bind(window)
  }
}

function timeoutScheduler() {
  return {
    next: function(cb) {
      return setTimeout(cb, 1000/60)
    },
    cancel: function (id) {
      return clearTimeout(id)
    }
  }
}

function makeAggregateRaf() {
  var frontBuffer = new Set();
  var backBuffer = new Set();
  var frameToken = 0;

  return {
    next: next,
    cancel: next,
    clearAll: clearAll
  }

  function clearAll() {
    frontBuffer.clear();
    backBuffer.clear();
    cancelAnimationFrame(frameToken);
    frameToken = 0;
  }

  function next(callback) {
    backBuffer.add(callback);
    renderNextFrame();
  }

  function renderNextFrame() {
    if (!frameToken) frameToken = requestAnimationFrame(renderFrame);
  }

  function renderFrame() {
    frameToken = 0;

    var t = backBuffer;
    backBuffer = frontBuffer;
    frontBuffer = t;

    frontBuffer.forEach(function(callback) {
      callback();
    });
    frontBuffer.clear();
  }

  function cancel(callback) {
    backBuffer.delete(callback);
  }
}