[MD settings] rtl sliders

chrome/browser/resources/settings/controls/settings_slider.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.
 
 /**
  * @fileoverview
  * settings-slider wraps a paper-slider. It maps the slider's values from a
  * linear UI range to a range of real values.  When |value| does not map exactly
  * to a tick mark, it interpolates to the nearest tick.
  *
  * Unlike paper-slider, there is no distinction between value and
  * immediateValue; when either changes, the |value| property is updated.
  */
 Polymer({
   is: 'settings-slider',
 
   behaviors: [CrPolicyPrefBehavior],
 
   properties: {
+    /** @type {?settings.DirectionDelegate} */
+    directionDelegate: {
+      observer: 'directionDelegateChanged_',
+      type: Object,
+      value: new settings.DirectionDelegateImpl(),
+    },
+
     /** @type {!chrome.settingsPrivate.PrefObject} */
     pref: Object,
 
     /** @type {!Array<number>} Values corresponding to each tick. */
     tickValues: {type: Array, value: []},
 
     min: Number,
 
     max: Number,
 
@@ skipping 15 matching lines @@
   ],
 
   /**
    * Sets the |pref.value| property to the value corresponding to the knob
    * position after a user action.
    * @private
    */
   onSliderChanged_: function() {
     var newValue;
     if (this.tickValues && this.tickValues.length > 0)
-      newValue = this.tickValues[this.$.slider.immediateValue];
+      newValue =
+          this.tickValues[this.convertValue_(this.$.slider.immediateValue)];
     else
-      newValue = this.$.slider.immediateValue;
+      newValue = this.convertValue_(this.$.slider.immediateValue);
 
     this.set('pref.value', newValue);
   },
 
   /** @private */
   computeDisableSlider_: function() {
     return this.disabled || this.isPrefEnforced();
   },
 
   /**
+   * Convert to/from the slider value and the preference value.
+   * TODO(dschuyler): This is a workaround for paper-slider which doesn't
+   * currently handle RTL. It'd be better to convert at a lower level.
+   * @private
+   */
+  convertValue_: function(sliderValue) {
+    return (this.directionDelegate.isRtl() && this.tickValues) ?
+        this.tickValues.length - 1 - sliderValue :
+        sliderValue;
+  },
+
+  /**
    * Updates the knob position when |pref.value| changes. If the knob is still
    * being dragged, this instead forces |pref.value| back to the current
    * position.
    * @private
    */
   valueChanged_: function() {
     // If |tickValues| is empty, simply set current value to the slider.
     if (this.tickValues.length == 0) {
-      this.$.slider.value = this.pref.value;
+      this.$.slider.value = this.convertValue_(this.pref.value);
       return;
     }
 
     // First update the slider settings if |tickValues| was set.
     var numTicks = Math.max(1, this.tickValues.length);
     this.$.slider.max = numTicks - 1;
     // Limit the number of ticks to 10 to keep the slider from looking too busy.
     /** @const */ var MAX_TICKS = 10;
     this.$.slider.snaps = numTicks < MAX_TICKS;
     this.$.slider.maxMarkers = numTicks < MAX_TICKS ? numTicks : 0;
 
     if (this.$.slider.dragging && this.tickValues.length > 0 &&
         this.pref.value != this.tickValues[this.$.slider.immediateValue]) {
       // The value changed outside settings-slider but we're still holding the
       // knob, so set the value back to where the knob was.
       // Async so we don't confuse Polymer's data binding.
       this.async(function() {
-        var newValue = this.tickValues[this.$.slider.immediateValue];
+        var newValue =
+            this.tickValues[this.convertValue_(this.$.slider.immediateValue)];
         this.set('pref.value', newValue);
       });
       return;
     }
 
     // Convert from the public |value| to the slider index (where the knob
     // should be positioned on the slider).
     var sliderIndex = this.tickValues.length > 0 ?
         this.tickValues.indexOf(/** @type {number} */ (this.pref.value)) :
         0;
     if (sliderIndex == -1) {
       // No exact match.
       sliderIndex = this.findNearestIndex_(
           this.tickValues,
           /** @type {number} */ (this.pref.value));
     }
-    this.$.slider.value = sliderIndex;
+    this.$.slider.value = this.convertValue_(sliderIndex);
   },
 
   /**
    * Returns the index of the item in |arr| closest to |value|.
    * @param {!Array<number>} arr
    * @param {number} value
    * @return {number}
    * @private
    */
   findNearestIndex_: function(arr, value) {
     var closestIndex;
     var minDifference = Number.MAX_VALUE;
     for (var i = 0; i < arr.length; i++) {
       var difference = Math.abs(arr[i] - value);
       if (difference < minDifference) {
         closestIndex = i;
         minDifference = difference;
       }
     }
 
     assert(typeof closestIndex != 'undefined');
     return closestIndex;
   },
 });