Famo.us - Fade in a Renderable's Opacity with a Quick Utility Function

fadeOpacity.js

/**
 * Utility function that allows for the quick creation of a StateModifier to modifiy the opacity of a renderable
 *
 * @param  {!number}   startOpacity The initial opacity of the object at the start of the transition (0-1)
 * @param  {!number}   endOpacity   The final opacity of the object at the end of the transition (0-1)
 * @param  {Transition}   transition  The curve function and duration that affects the opacity
 * @param  {function}   callback    Callback function after the transition
 * @return {StateModifier}
 * 
 * @example
 * // Fades in an object from 0 to full opacity using the inSine transition from Easing.js
 * // Logs "Fade Complete!" when done.
 * mainContext.add(fadeOpacity(0, 1, 'inSine', function(){ console.log('Fade Complete!'); } )
 *            .add(mySurface);
 */
function fadeOpacity(startOpacity, endOpacity, transition, callback) {
  var stateModifier = new StateModifier();
  stateModifier.setOpacity(startOpacity);
  stateModifier.setOpacity(endOpacity, transition, callback);
  
  return stateModifier;
}