Bug 663023 - Cache getDPI calls. r=mbrubeck

mobile/chrome/content/Util.js

@@ -162,7 +162,7 @@ let Util = {
   },
 
   isTablet: function isTablet() {
-    let dpi = Util.getWindowUtils(window).displayDPI;
+    let dpi = this.displayDPI;
     if (dpi <= 96)
       return (window.innerWidth > 1024);
 
@@ -188,6 +188,11 @@ let Util = {
       return ViewableAreaObserver.isKeyboardOpened;
 
     return (sendSyncMessage("Content:IsKeyboardOpened", {}))[0];
+  },
+
+  get displayDPI() {
+    delete this.displayDPI;
+    return this.displayDPI = this.getWindowUtils(window).displayDPI;
   }
 };
 

mobile/chrome/content/browser-ui.js

@@ -364,7 +364,7 @@ var BrowserUI = {
           return true;
         case -1: {
           let threshold = Services.prefs.getIntPref("widget.ime.android.fullscreen_threshold");
-          let dpi = Util.getWindowUtils(window).displayDPI;
+          let dpi = Util.displayDPI;
           return (window.innerHeight * 100 < threshold * dpi);
         }
       }

mobile/chrome/content/browser.js

@@ -1112,7 +1112,7 @@ var Browser = {
     if (prefValue > 0)
       return prefValue / 100;
 
-    let dpi = this.windowUtils.displayDPI;
+    let dpi = Util.displayDPI;
     if (dpi < 200) // Includes desktop displays, and LDPI and MDPI Android devices
       return 1;
     else if (dpi < 300) // Includes Nokia N900, and HDPI Android devices
@@ -1809,7 +1809,7 @@ const ContentTouchHandler = {
   panningPrevented: false,
 
   updateCanCancel: function(aX, aY) {
-    let dpi = Browser.windowUtils.displayDPI;
+    let dpi = Util.displayDPI;
 
     const kSafetyX = Services.prefs.getIntPref("dom.w3c_touch_events.safetyX") / 240 * dpi;
     const kSafetyY = Services.prefs.getIntPref("dom.w3c_touch_events.safetyY") / 240 * dpi;

mobile/chrome/content/content.js

@@ -68,7 +68,10 @@ const ElementTouchHelper = {
 
   /* Retrieve the closest element to a point by looking at borders position */
   getClosest: function getClosest(aWindowUtils, aX, aY) {
-    let dpiRatio = aWindowUtils.displayDPI / kReferenceDpi;
+    if (!this.dpiRatio)
+      this.dpiRatio = aWindowUtils.displayDPI / kReferenceDpi;
+
+    let dpiRatio = this.dpiRatio;
 
     let target = aWindowUtils.elementFromPoint(aX, aY,
                                                true,   /* ignore root scroll frame*/

mobile/chrome/content/input.js

@@ -118,7 +118,7 @@ function MouseModule() {
   this._mouseOverTimeout = new Util.Timeout(this._doMouseOver.bind(this));
   this._longClickTimeout = new Util.Timeout(this._doLongClick.bind(this));
 
-  this._doubleClickRadius = Util.getWindowUtils(window).displayDPI * kDoubleClickRadius;
+  this._doubleClickRadius = Util.displayDPI * kDoubleClickRadius;
 
   window.addEventListener("mousedown", this, true);
   window.addEventListener("mouseup", this, true);
@@ -570,7 +570,7 @@ MouseModule.prototype = {
 var ScrollUtils = {
   // threshold in pixels for sensing a tap as opposed to a pan
   get tapRadius() {
-    let dpi = Util.getWindowUtils(window).displayDPI;
+    let dpi = Util.displayDPI;
 
     delete this.tapRadius;
     return this.tapRadius = Services.prefs.getIntPref("ui.dragThresholdX") / 240 * dpi;
@@ -686,7 +686,7 @@ var ScrollUtils = {
  */
 function DragData() {
   this._domUtils = Cc["@mozilla.org/inspector/dom-utils;1"].getService(Ci.inIDOMUtils);
-  this._lockRevertThreshold = Util.getWindowUtils(window).displayDPI * kAxisLockRevertThreshold;
+  this._lockRevertThreshold = Util.displayDPI * kAxisLockRevertThreshold;
   this.reset();
 };