<!– @license Copyright © 2016 The Polymer Project Authors. All rights reserved. This code may only be used under the BSD style license found at polymer.github.io/LICENSE.txt The complete set of authors may be found at polymer.github.io/AUTHORS.txt The complete set of contributors may be found at polymer.github.io/CONTRIBUTORS.txt Code distributed by Google as part of the polymer project is also subject to an additional IP rights grant found at polymer.github.io/PATENTS.txt –>

<link rel=“import” href=“../app-scroll-effects-behavior.html”>

<script>

/**
 * Upon scrolling past a threshold, fade in the rear background layer and fade out the front
 * background layer (opacity CSS transitioned over time).
 *
 *
 */
Polymer.AppLayout.registerEffect('fade-background', {
  /** @this Polymer.AppLayout.ElementWithBackground */
  setUp: function setUp(config) {
    var fx = {};
    var duration = config.duration || '0.5s';
    fx.backgroundFrontLayer = this._getDOMRef('backgroundFrontLayer');
    fx.backgroundRearLayer = this._getDOMRef('backgroundRearLayer');
    fx.backgroundFrontLayer.style.willChange = 'opacity';
    fx.backgroundFrontLayer.style.webkitTransform = 'translateZ(0)';
    fx.backgroundFrontLayer.style.transitionProperty = 'opacity';
    fx.backgroundFrontLayer.style.transitionDuration = duration;
    fx.backgroundRearLayer.style.willChange = 'opacity';
    fx.backgroundRearLayer.style.webkitTransform = 'translateZ(0)';
    fx.backgroundRearLayer.style.transitionProperty = 'opacity';
    fx.backgroundRearLayer.style.transitionDuration = duration;
    this._fxFadeBackground = fx;
  },
  /** @this Polymer.AppLayout.ElementWithBackground */
  run: function run(p, y) {
    var fx = this._fxFadeBackground;
    if (p >= 1) {
      fx.backgroundFrontLayer.style.opacity = 0;
      fx.backgroundRearLayer.style.opacity = 1;
    } else {
      fx.backgroundFrontLayer.style.opacity = 1;
      fx.backgroundRearLayer.style.opacity = 0;
    }
  },
  /** @this Polymer.AppLayout.ElementWithBackground */
  tearDown: function tearDown() {
    delete this._fxFadeBackground;
  }
});

</script>