Issue #1355 - Avoid unnecessary work in nsIFrame::BuildDisplayListForStackingContext() and nsIFrame::BuildDisplayListForChild() and Cleanup DescendIntoChild

Bug 1441796 - Part 1: Optimize the (pseudo)-stacking context conditions

Bug 1441796 - Part 3: Reuse the results in nsIFrame::BuildDisplayListForStackingContext() for ChildrenHavePerspective(), IsTransformed(), and Combines3DTransformWithAncestors()

Bug 1512244 - Part 1: Cleanup DescendIntoChild

2 files changed, 27 insertions, 10 deletions

diff --git a/layout/base/nsDisplayList.cpp b/layout/base/nsDisplayList.cpp
index b08fe4219a..a869564a4f 100644
--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -1009,8 +1009,22 @@ nsDisplayListBuilder::EnterPresShell(nsIFrame* aReferenceFrame,
   }
   state->mInsidePointerEventsNoneDoc = pointerEventsNone;
 
-  if (!buildCaret)
+  state->mPresShellIgnoreScrollFrame =
+      state->mPresShell->IgnoringViewportScrolling()
+          ? state->mPresShell->GetRootScrollFrame()
+          : nullptr;
+
+   nsPresContext* pc = aReferenceFrame->PresContext();
+   nsCOMPtr<nsIDocShell> docShell = pc->GetDocShell();
+   if (docShell) {
+     docShell->GetWindowDraggingAllowed(&mWindowDraggingAllowed);
+   }
+
+   mIsInChromePresContext = pc->IsChrome();
+
+  if (!buildCaret) {
     return;
+  }
 
   RefPtr<nsCaret> caret = state->mPresShell->GetCaret();
   state->mCaretFrame = caret->GetPaintGeometry(&state->mCaretRect);
@@ -1018,13 +1032,6 @@ nsDisplayListBuilder::EnterPresShell(nsIFrame* aReferenceFrame,
     mFramesMarkedForDisplay.AppendElement(state->mCaretFrame);
     MarkFrameForDisplay(state->mCaretFrame, nullptr);
   }
-
-  nsPresContext* pc = aReferenceFrame->PresContext();
-  nsCOMPtr<nsIDocShell> docShell = pc->GetDocShell();
-  if (docShell) {
-    docShell->GetWindowDraggingAllowed(&mWindowDraggingAllowed);
-  }
-  mIsInChromePresContext = pc->IsChrome();
 }
 
 // A non-blank paint is a paint that does not just contain the canvas background.
diff --git a/layout/base/nsDisplayList.h b/layout/base/nsDisplayList.h
index 1b2010d339..3aeb20d196 100644
--- a/layout/base/nsDisplayList.h
+++ b/layout/base/nsDisplayList.h
@@ -520,6 +520,14 @@ public:
    * Get the caret associated with the current presshell.
    */
   nsCaret* GetCaret();
+
+   /**
+    * Returns the root scroll frame for the current PresShell, if the PresShell
+    * is ignoring viewport scrolling.
+    */
+   nsIFrame* GetPresShellIgnoreScrollFrame() {
+     return CurrentPresShellState()->mPresShellIgnoreScrollFrame;
+   }
   /**
    * Notify the display list builder that we're entering a presshell.
    * aReferenceFrame should be a frame in the new presshell.
@@ -805,10 +813,11 @@ public:
   friend class AutoSaveRestorePerspectiveIndex;
   class AutoSaveRestorePerspectiveIndex {
   public:
-    AutoSaveRestorePerspectiveIndex(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
+    AutoSaveRestorePerspectiveIndex(nsDisplayListBuilder* aBuilder,
+                                    const bool aChildrenHavePerspective)
       : mBuilder(nullptr)
     {
-      if (aFrame->ChildrenHavePerspective()) {
+      if (aChildrenHavePerspective) {
         mBuilder = aBuilder;
         mCachedItemIndex = aBuilder->mPerspectiveItemIndex;
         aBuilder->mPerspectiveItemIndex = 0;
@@ -1175,6 +1184,7 @@ private:
     nsRect        mCaretRect;
     uint32_t      mFirstFrameMarkedForDisplay;
     bool          mIsBackgroundOnly;
+    nsIFrame*     mPresShellIgnoreScrollFrame;
     // This is a per-document flag turning off event handling for all content
     // in the document, and is set when we enter a subdocument for a pointer-
     // events:none frame.