bug 674373 pt 5 - provide a fullZoom API in nsIDOMWindowUtils, and use this rather than inferring zoom from CSS to device pixel ratio. r=roc

browser/base/content/browser.js

@@ -733,7 +733,7 @@ const gFormSubmitObserver = {
         offset = parseInt(style.paddingLeft) + parseInt(style.borderLeftWidth);
       }
 
-      offset = Math.round(offset * utils.screenPixelsPerCSSPixel);
+      offset = Math.round(offset * utils.fullZoom);
 
       position = "after_start";
     }
@@ -7551,9 +7551,9 @@ var MousePosTracker = {
   },
 
   handleEvent: function (event) {
-    var screenPixelsPerCSSPixel = this._windowUtils.screenPixelsPerCSSPixel;
-    this._x = event.screenX / screenPixelsPerCSSPixel - window.mozInnerScreenX;
-    this._y = event.screenY / screenPixelsPerCSSPixel - window.mozInnerScreenY;
+    var fullZoom = this._windowUtils.fullZoom;
+    this._x = event.screenX / fullZoom - window.mozInnerScreenX;
+    this._y = event.screenY / fullZoom - window.mozInnerScreenY;
 
     this._listeners.forEach(function (listener) {
       try {

browser/devtools/highlighter/highlighter.jsm

@@ -694,7 +694,7 @@ Highlighter.prototype = {
     this.zoom =
       this.win.QueryInterface(Ci.nsIInterfaceRequestor)
       .getInterface(Ci.nsIDOMWindowUtils)
-      .screenPixelsPerCSSPixel;
+      .fullZoom;
   },
 
   /////////////////////////////////////////////////////////////////////////

browser/devtools/shared/LayoutHelpers.jsm

@@ -175,7 +175,7 @@ LayoutHelpers = {
     let zoom =
       aWin.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
         .getInterface(Components.interfaces.nsIDOMWindowUtils)
-        .screenPixelsPerCSSPixel;
+        .fullZoom;
 
     // adjust rect for zoom scaling
     let aRectScaled = {};

content/events/test/test_bug574663.html

@@ -62,7 +62,7 @@ function runTest() {
 
       let [ctrlKey, isMomentum] = outstandingTests.shift();
       let scrollTopBefore = scrollbox.scrollTop;
-      let zoomFactorBefore = winUtils.screenPixelsPerCSSPixel;
+      let zoomFactorBefore = winUtils.fullZoom;
       sendTouchpadScrollMotion(scrollbox, 1, ctrlKey, isMomentum);
 
       setTimeout(function () {
@@ -70,14 +70,14 @@ function runTest() {
         if (!ctrlKey) {
           let postfix = isMomentum ? ", even after releasing the touchpad" : "";
           // Normal scroll: scroll
-          is(winUtils.screenPixelsPerCSSPixel, zoomFactorBefore, "Normal scrolling shouldn't change zoom" + postfix);
+          is(winUtils.fullZoom, zoomFactorBefore, "Normal scrolling shouldn't change zoom" + postfix);
           isnot(scrollbox.scrollTop, scrollTopBefore, "Normal scrolling should scroll" + postfix);
         } else {
           if (!isMomentum) {
-            isnot(winUtils.screenPixelsPerCSSPixel, zoomFactorBefore, "Ctrl-scrolling should zoom while the user is touching the touchpad");
+            isnot(winUtils.fullZoom, zoomFactorBefore, "Ctrl-scrolling should zoom while the user is touching the touchpad");
             is(scrollbox.scrollTop, scrollTopBefore, "Ctrl-scrolling shouldn't scroll while the user is touching the touchpad");
           } else {
-            is(winUtils.screenPixelsPerCSSPixel, zoomFactorBefore, "Momentum scrolling shouldn't zoom, even when pressing Ctrl");
+            is(winUtils.fullZoom, zoomFactorBefore, "Momentum scrolling shouldn't zoom, even when pressing Ctrl");
             isnot(scrollbox.scrollTop, scrollTopBefore, "Momentum scrolling should scroll, even when pressing Ctrl");
           }
         }

dom/base/nsDOMWindowUtils.cpp

@@ -1510,6 +1510,25 @@ nsDOMWindowUtils::GetScreenPixelsPerCSSPixel(float* aScreenPixels)
   return window->GetDevicePixelRatio(aScreenPixels);
 }
 
+NS_IMETHODIMP
+nsDOMWindowUtils::GetFullZoom(float* aFullZoom)
+{
+  *aFullZoom = 1.0f;
+
+  if (!nsContentUtils::IsCallerTrustedForRead()) {
+    return NS_ERROR_DOM_SECURITY_ERR;
+  }
+
+  nsPresContext* presContext = GetPresContext();
+  if (!presContext) {
+    return NS_OK;
+  }
+
+  *aFullZoom = presContext->DeviceContext()->GetPixelScale();
+
+  return NS_OK;
+}
+ 
 NS_IMETHODIMP
 nsDOMWindowUtils::DispatchDOMEventViaPresShell(nsIDOMNode* aTarget,
                                                nsIDOMEvent* aEvent,

dom/interfaces/base/nsIDOMWindowUtils.idl

@@ -40,7 +40,7 @@ interface nsIDOMTouch;
 interface nsIDOMClientRect;
 interface nsIURI;
 
-[scriptable, uuid(90d8e97b-2c61-4c05-9f1c-e568d22f5bdc)]
+[scriptable, uuid(47405734-D827-44AE-AC01-EF10E80F5D04)]
 interface nsIDOMWindowUtils : nsISupports {
 
   /**
@@ -697,6 +697,14 @@ interface nsIDOMWindowUtils : nsISupports {
    */
   readonly attribute float screenPixelsPerCSSPixel;
 
+  /**
+   * Get the current zoom factor.
+   * This is _approximately_ the same as nsIMarkupDocumentViewer.fullZoom,
+   * but takes into account Gecko's quantization of the zoom factor, which is
+   * implemented by adjusting the (integer) number of appUnits per devPixel.
+   */
+  readonly attribute float fullZoom;
+
   /**
    * Dispatches aEvent via the nsIPresShell object of the window's document.
    * The event is dispatched to aTarget, which should be an object

gfx/src/nsDeviceContext.cpp

@@ -734,4 +734,6 @@ nsDeviceContext::UpdateScaledAppUnits()
 {
     mAppUnitsPerDevPixel =
         NS_MAX(1, NSToIntRound(float(mAppUnitsPerDevNotScaledPixel) / mPixelScale));
+    // adjust mPixelScale to reflect appunit rounding
+    mPixelScale = float(mAppUnitsPerDevNotScaledPixel) / mAppUnitsPerDevPixel;
 }

gfx/src/nsDeviceContext.h

@@ -222,6 +222,11 @@ public:
      */
     bool SetPixelScale(float aScale);
 
+    /**
+     * Returns the pixel scaling factor (page zoom factor) applied.
+     */
+    float GetPixelScale() const { return mPixelScale; }
+
     /**
      * True if this device context was created for printing.
      */

layout/style/test/test_moz_device_pixel_ratio.html

@@ -38,11 +38,11 @@ function run() {
     return window.getComputedStyle(document.getElementById(divName), null).visibility == "visible";
   }
 
-  function getZoomRatio() {
+  function getScreenPixelsPerCSSPixel() {
     return SpecialPowers.DOMWindowUtils.screenPixelsPerCSSPixel;
   }
 
-  var screenPixelsPerCSSPixel = getZoomRatio();
+  var screenPixelsPerCSSPixel = getScreenPixelsPerCSSPixel();
   var baseRatio = 1.0 * screenPixelsPerCSSPixel;
   var doubleRatio = 2.0 * screenPixelsPerCSSPixel;
   var halfRatio = 0.5 * screenPixelsPerCSSPixel;
@@ -61,10 +61,10 @@ function run() {
 
   ok(isVisible("zoom1"), "Base ratio rule should apply at base zoom level");
   ok(!isVisible("zoom2") && !isVisible("zoom3"), "no other rules should apply");
-  var origZoom = zoom(2 * screenPixelsPerCSSPixel);
+  var origZoom = zoom(2);
   ok(isVisible("zoom2"), "Double ratio rule should apply at double zoom level");
   ok(!isVisible("zoom1") && !isVisible("zoom3"), "no other rules should apply");
-  zoom(0.5 * screenPixelsPerCSSPixel);
+  zoom(0.5);
   ok(isVisible("zoom3"), "Half ratio rule should apply at half zoom level");
   ok(!isVisible("zoom1") && !isVisible("zoom2"), "no other rules should apply");
   zoom(origZoom);