VrShell: Allow native control of UI element opacity.

chrome/browser/resources/vr_shell/vr_shell_ui_api.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var api = {};
 
 /**
  * Enumeration of scene update commands.
  * @enum {number}
  * @const
  */
 api.Command = {
   'ADD_ELEMENT': 0,
   'UPDATE_ELEMENT': 1,
   'REMOVE_ELEMENT': 2,
   'ADD_ANIMATION': 3,
   'REMOVE_ANIMATION': 4
 };
 
 /**
  * Sends one or more commands to native scene management. Commands are used
  * to add, modify or remove elements and animations. For examples of how to
  * format command parameters, refer to examples in scene.js.
  * @param {Array<Object>} commands
  */
 api.sendCommands = function(commands) {
-  chrome.send('updateScene', commands);
+  if (commands.length > 0) {
+    chrome.send('updateScene', commands);
+  }
 };
 
 /**
  * Enumeration of valid Anchroing for X axis.
  * An element can either be anchored to the left, right, or center of the main
  * content rect (or it can be absolutely positioned using NONE). Any
  * translations applied will be relative to this anchoring.
  * @enum {number}
  * @const
  */
@@ skipping 169 matching lines @@
   /**
    * Hit-testable implies that the reticle will hit the element, if visible.
    * @param {boolean} testable
    */
   setHitTestable(testable) {
     this.properties['hitTestable'] = !!testable;
   }
 
   /**
    * Causes an element to be rendered relative to the field of view, rather
-   * than the scene.  Elements locked in this way should not have a parent.
+   * than the scene. Elements locked in this way should not have a parent.
    * @param {boolean} locked
    */
   setLockToFieldOfView(locked) {
     this.properties['lockToFov'] = !!locked;
   }
+
+  /**
+   * Causes an element to be rendered with a specified opacity, between 0.0 and
+   * 1.0. Opacity is inherited by children.
+   * @param {number} opacity
+   */
+  setOpacity(opacity) {
+    this.properties['opacity'] = opacity;
+  }
 };
 
 /**
  * Represents a new UI element. This object builds on UiElementUpdate,
  * forcing the underlying texture coordinates to be specified.
  * @struct
  */
 api.UiElement = class extends api.UiElementUpdate {
   /**
    * Constructor of UiElement.
@@ skipping 17 matching lines @@
 /**
  * Enumeration of animatable properties.
  * @enum {number}
  * @const
  */
 api.Property = {
   'COPYRECT': 0,
   'SIZE': 1,
   'TRANSLATION': 2,
   'SCALE': 3,
-  'ROTATION': 4
+  'ROTATION': 4,
+  'OPACITY': 5
 };
 
 /**
  * Enumeration of easing type.
  * @enum {number}
  * @const
  */
 api.Easing = {
   'LINEAR': 0,
   'CUBICBEZIER': 1,
@@ skipping 81 matching lines @@
    * @param {number} x
    * @param {number} y
    * @param {number} z
    */
   setTranslation(x, y, z) {
     this.property = api.Property.TRANSLATION;
     this.to.x = x;
     this.to.y = y;
     this.to.z = z;
   }
+
+  /**
+   * Set the animation's final element opacity.
+   * @param {number} opacity
+   */
+  setOpacity(opacity) {
+    this.property = api.Property.OPACITY;
+    this.to.x = opacity;
+  }
 };