Bug 1042959 - Ensure that we always use the actual old screen size in HandlePossibleViewportChange. r=botond

dom/ipc/TabChild.cpp

@@ -78,6 +78,7 @@
 #include "mozilla/gfx/Matrix.h"
 #include "UnitTransforms.h"
 #include "ClientLayerManager.h"
+#include "LayersLogging.h"
 
 #include "nsColorPickerProxy.h"
 
@@ -88,6 +89,9 @@
 #define BROWSER_ELEMENT_CHILD_SCRIPT \
     NS_LITERAL_STRING("chrome://global/content/BrowserElementChild.js")
 
+#define TABC_LOG(...)
+// #define TABC_LOG(...) printf_stderr("TABC: " __VA_ARGS__)
+
 using namespace mozilla;
 using namespace mozilla::dom;
 using namespace mozilla::dom::ipc;
@@ -174,12 +178,16 @@ TabChildBase::InitializeRootMetrics()
   // as the resolution.
   mLastRootMetrics.mResolution = mLastRootMetrics.mCumulativeResolution / LayoutDeviceToParentLayerScale(1);
   mLastRootMetrics.SetScrollOffset(CSSPoint(0, 0));
+
+  TABC_LOG("After InitializeRootMetrics, mLastRootMetrics is %s\n",
+    Stringify(mLastRootMetrics).c_str());
 }
 
 void
 TabChildBase::SetCSSViewport(const CSSSize& aSize)
 {
   mOldViewportSize = aSize;
+  TABC_LOG("Setting CSS viewport to %s\n", Stringify(aSize).c_str());
 
   if (mContentDocumentIsDisplayed) {
     nsCOMPtr<nsIDOMWindowUtils> utils(GetDOMWindowUtils());
@@ -213,12 +221,15 @@ TabChildBase::GetPageSize(nsCOMPtr<nsIDocument> aDocument, const CSSSize& aViewp
 }
 
 bool
-TabChildBase::HandlePossibleViewportChange()
+TabChildBase::HandlePossibleViewportChange(const ScreenIntSize& aOldScreenSize)
 {
   if (!IsAsyncPanZoomEnabled()) {
     return false;
   }
 
+  TABC_LOG("HandlePossibleViewportChange aOldScreenSize=%s mInnerSize=%s\n",
+    Stringify(aOldScreenSize).c_str(), Stringify(mInnerSize).c_str());
+
   nsCOMPtr<nsIDocument> document(GetDocument());
   nsCOMPtr<nsIDOMWindowUtils> utils(GetDOMWindowUtils());
 
@@ -249,6 +260,8 @@ TabChildBase::HandlePossibleViewportChange()
     return false;
   }
 
+  TABC_LOG("HandlePossibleViewportChange mOldViewportSize=%s viewport=%s\n",
+    Stringify(mOldViewportSize).c_str(), Stringify(viewport).c_str());
   CSSSize oldBrowserSize = mOldViewportSize;
   mLastRootMetrics.mViewport.SizeTo(viewport);
   if (oldBrowserSize == CSSSize()) {
@@ -269,9 +282,7 @@ TabChildBase::HandlePossibleViewportChange()
     return false;
   }
 
-  ScreenIntSize oldScreenSize = ViewAs<ScreenPixel>(
-      RoundedToInt(mLastRootMetrics.mCompositionBounds).Size(),
-      PixelCastJustification::ScreenToParentLayerForRoot);
+  ScreenIntSize oldScreenSize = aOldScreenSize;
   if (oldScreenSize == ScreenIntSize()) {
     oldScreenSize = mInnerSize;
   }
@@ -748,7 +759,7 @@ TabChild::HandleEvent(nsIDOMEvent* aEvent)
   if (eventType.EqualsLiteral("DOMMetaAdded")) {
     // This meta data may or may not have been a meta viewport tag. If it was,
     // we should handle it immediately.
-    HandlePossibleViewportChange();
+    HandlePossibleViewportChange(mInnerSize);
   }
 
   return NS_OK;
@@ -799,7 +810,7 @@ TabChild::Observe(nsISupports *aSubject,
           InitializeRootMetrics();
           utils->SetResolution(mLastRootMetrics.mResolution.scale,
                                mLastRootMetrics.mResolution.scale);
-          HandlePossibleViewportChange();
+          HandlePossibleViewportChange(mInnerSize);
         }
       }
     }
@@ -1750,6 +1761,7 @@ TabChild::RecvUpdateDimensions(const nsRect& rect, const nsIntSize& size, const
     }
 
     mOrientation = orientation;
+    ScreenIntSize oldScreenSize = mInnerSize;
     mInnerSize = ScreenIntSize::FromUnknownSize(
       gfx::IntSize(size.width, size.height));
     mWidget->Resize(0, 0, size.width, size.height,
@@ -1767,7 +1779,7 @@ TabChild::RecvUpdateDimensions(const nsRect& rect, const nsIntSize& size, const
       InitializeRootMetrics();
     }
 
-    HandlePossibleViewportChange();
+    HandlePossibleViewportChange(oldScreenSize);
 
     return true;
 }

dom/ipc/TabChild.h

@@ -178,7 +178,7 @@ public:
     // viewport data on a document may have changed. If it didn't
     // change, this function doesn't do anything.  However, it should
     // not be called all the time as it is fairly expensive.
-    bool HandlePossibleViewportChange();
+    bool HandlePossibleViewportChange(const ScreenIntSize& aOldScreenSize);
     virtual bool DoUpdateZoomConstraints(const uint32_t& aPresShellId,
                                          const mozilla::layers::FrameMetrics::ViewID& aViewId,
                                          const bool& aIsRoot,