Bug 1554861 - Disable clipping and scaling for top-level remote browsers to resolve regressions. r=mattwoodrow

Differential Revision: https://phabricator.services.mozilla.com/D35702

--HG--
extra : moz-landing-system : lando

dom/ipc/BrowserChild.cpp

@@ -3332,16 +3332,16 @@ ScreenIntSize BrowserChild::GetInnerSize() {
       innerSize, PixelCastJustification::LayoutDeviceIsScreenForTabDims);
 };
 
-LayoutDeviceIntRect BrowserChild::GetVisibleRect() {
-  CSSRect visibleRect;
+Maybe<LayoutDeviceIntRect> BrowserChild::GetVisibleRect() const {
   if (mIsTopLevel) {
     // We are conservative about visible rects for top-level browsers to avoid
     // artifacts when resizing
-    visibleRect = CSSRect(CSSPoint(), mUnscaledInnerSize);
-  } else {
-    visibleRect = CSSPixel::FromAppUnits(mEffectsInfo.mVisibleRect);
+    return Nothing();
   }
-  return RoundedToInt(visibleRect * mPuppetWidget->GetDefaultScale());
+  CSSRect visibleRectCSS = CSSPixel::FromAppUnits(mEffectsInfo.mVisibleRect);
+  LayoutDeviceIntRect visibleRectLD =
+      RoundedToInt(visibleRectCSS * mPuppetWidget->GetDefaultScale());
+  return Some(visibleRectLD);
 }
 
 ScreenIntRect BrowserChild::GetOuterRect() {

dom/ipc/BrowserChild.h

@@ -239,6 +239,8 @@ class BrowserChild final : public nsMessageManagerScriptExecutor,
     return mBrowserChildMessageManager;
   }
 
+  bool IsTopLevel() const { return mIsTopLevel; }
+
   /**
    * MessageManagerCallback methods that we override.
    */
@@ -549,7 +551,7 @@ class BrowserChild final : public nsMessageManagerScriptExecutor,
 
   ScreenIntSize GetInnerSize();
 
-  LayoutDeviceIntRect GetVisibleRect();
+  Maybe<LayoutDeviceIntRect> GetVisibleRect() const;
 
   // Call RecvShow(nsIntSize(0, 0)) and block future calls to RecvShow().
   void DoFakeShow(const ShowInfo& aShowInfo);

layout/base/nsLayoutUtils.cpp

@@ -3792,11 +3792,14 @@ nsresult nsLayoutUtils::PaintFrame(gfxContext* aRenderingContext,
 
   // If we are in a remote browser, then apply clipping from ancestor browsers
   if (BrowserChild* browserChild = BrowserChild::GetFrom(presShell)) {
-    LayoutDeviceIntRect unscaledVisibleRect = browserChild->GetVisibleRect();
-    CSSRect visibleRect =
-        unscaledVisibleRect / presContext->CSSToDevPixelScale();
-    rootVisualOverflow.IntersectRect(rootVisualOverflow,
-                                     CSSPixel::ToAppUnits(visibleRect));
+    Maybe<LayoutDeviceIntRect> unscaledVisibleRect =
+        browserChild->GetVisibleRect();
+    if (unscaledVisibleRect) {
+      CSSRect visibleRect =
+          *unscaledVisibleRect / presContext->CSSToDevPixelScale();
+      rootVisualOverflow.IntersectRect(rootVisualOverflow,
+                                       CSSPixel::ToAppUnits(visibleRect));
+    }
   }
 
   nsIFrame* rootScrollFrame = presShell->GetRootScrollFrame();

layout/painting/nsDisplayList.cpp

@@ -2880,8 +2880,10 @@ FrameLayerBuilder* nsDisplayList::BuildLayers(nsDisplayListBuilder* aBuilder,
 
     // If we are in a remote browser, then apply scaling from ancestor browsers
     if (BrowserChild* browserChild = BrowserChild::GetFrom(presShell)) {
-      resolutionX *= browserChild->GetEffectsInfo().mScaleX;
-      resolutionY *= browserChild->GetEffectsInfo().mScaleY;
+      if (!browserChild->IsTopLevel()) {
+        resolutionX *= browserChild->GetEffectsInfo().mScaleX;
+        resolutionY *= browserChild->GetEffectsInfo().mScaleY;
+      }
     }
 
     ContainerLayerParameters containerParameters(resolutionX, resolutionY);

widget/PuppetWidget.cpp

@@ -1159,10 +1159,12 @@ LayoutDeviceIntRect PuppetWidget::GetScreenBounds() {
 }
 
 LayoutDeviceIntSize PuppetWidget::GetCompositionSize() {
-  if (!mBrowserChild) {
+  Maybe<LayoutDeviceIntRect> visibleRect =
+      mBrowserChild ? mBrowserChild->GetVisibleRect() : Nothing();
+  if (!visibleRect) {
     return nsBaseWidget::GetCompositionSize();
   }
-  return mBrowserChild->GetVisibleRect().Size();
+  return visibleRect->Size();
 }
 
 uint32_t PuppetWidget::GetMaxTouchPoints() const {