Bug 1725555 - patch 3 - Also use continuations array to accelerate nsTextFrame::SelectionStateChanged. r=emilio

After CollectClientRectsAndText is eliminated from the profiles here, SelectionStateChanged
is the next obvious hotspot, and it can similarly be accelerated by binary-searching the continuations.

Depends on D122999

Differential Revision: https://phabricator.services.mozilla.com/D123000

dom/base/nsRange.cpp

@@ -2648,32 +2648,8 @@ static nsresult GetPartialTextRect(RectCallback* aCallback,
     nsIFrame* relativeTo =
         nsLayoutUtils::GetContainingBlockForClientRect(textFrame);
 
-    // Try to binary-search the list of continuations for the starting point.
-    // (GetContinuations is fallible; if it returns nullptr, we'll just start
-    // from the beginning.)
-    nsTArray<nsTextFrame*>* continuations = textFrame->GetContinuations();
-    nsTextFrame* f = textFrame;
-    if (continuations) {
-      size_t index;
-      if (BinarySearchIf(
-              *continuations, 0, continuations->Length(),
-              [=](nsTextFrame* aFrame) -> int {
-                if (aStartOffset < aFrame->GetContentOffset()) {
-                  return -1;
-                }
-                if (aStartOffset > aFrame->GetContentOffset()) {
-                  return 1;
-                }
-                return 0;
-              },
-              &index)) {
-        f = (*continuations)[index];
-      } else {
-        f = (*continuations)[index ? index - 1 : 0];
-      }
-    }
-
-    for (; f; f = static_cast<nsTextFrame*>(f->GetNextContinuation())) {
+    for (nsTextFrame* f = textFrame->FindContinuationForOffset(aStartOffset); f;
+         f = static_cast<nsTextFrame*>(f->GetNextContinuation())) {
       int32_t fstart = f->GetContentOffset(), fend = f->GetContentEnd();
       if (fend <= aStartOffset) {
         continue;

layout/generic/nsTextFrame.cpp

@@ -4494,8 +4494,6 @@ class nsContinuingTextFrame final : public nsTextFrame {
   nsIFrame* FirstInFlow() const final;
   nsTextFrame* FirstContinuation() const final { return mFirstContinuation; };
 
-  nsTArray<nsTextFrame*>* GetContinuations() final { return nullptr; }
-
   void AddInlineMinISize(gfxContext* aRenderingContext,
                          InlineMinISizeData* aData) final;
   void AddInlinePrefISize(gfxContext* aRenderingContext,
@@ -7503,6 +7501,33 @@ bool nsTextFrame::IsFrameSelected() const {
   return mIsSelected == nsTextFrame::SelectionState::Selected;
 }
 
+nsTextFrame* nsTextFrame::FindContinuationForOffset(int32_t aOffset) {
+  // Use a continuations array to accelerate finding the first continuation
+  // of interest, if possible.
+  MOZ_ASSERT(!GetPrevContinuation(), "should be called on the primary frame");
+  auto* continuations = GetContinuations();
+  nsTextFrame* f = this;
+  if (continuations) {
+    size_t index;
+    if (BinarySearchIf(
+            *continuations, 0, continuations->Length(),
+            [=](nsTextFrame* aFrame) -> int {
+              return aOffset - aFrame->GetContentOffset();
+            },
+            &index)) {
+      f = (*continuations)[index];
+    } else {
+      f = (*continuations)[index ? index - 1 : 0];
+    }
+  }
+
+  while (f && f->GetContentEnd() <= aOffset) {
+    f = f->GetNextContinuation();
+  }
+
+  return f;
+}
+
 void nsTextFrame::SelectionStateChanged(uint32_t aStart, uint32_t aEnd,
                                         bool aSelected,
                                         SelectionType aSelectionType) {
@@ -7513,13 +7538,12 @@ void nsTextFrame::SelectionStateChanged(uint32_t aStart, uint32_t aEnd,
   InvalidateSelectionState();
 
   // Selection is collapsed, which can't affect text frame rendering
-  if (aStart == aEnd) return;
-
-  nsTextFrame* f = this;
-  while (f && f->GetContentEnd() <= int32_t(aStart)) {
-    f = f->GetNextContinuation();
+  if (aStart == aEnd) {
+    return;
   }
 
+  nsTextFrame* f = FindContinuationForOffset(aStart);
+
   nsPresContext* presContext = PresContext();
   while (f && f->GetContentOffset() < int32_t(aEnd)) {
     // We may need to reflow to recompute the overflow area for

layout/generic/nsTextFrame.h

@@ -784,10 +784,11 @@ class nsTextFrame : public nsIFrame {
 
   nsRect WebRenderBounds();
 
-  // Return pointer to an array of all frames in the continuation chain, or
-  // null if we're too short of memory. (This is only meant to be called on the
-  // first text frame in the chain; continuations will always return null.)
-  virtual nsTArray<nsTextFrame*>* GetContinuations();
+  // Find the continuation (which may be this frame itself) containing the
+  // given offset. Note that this may return null, if the offset is beyond the
+  // text covered by the continuation chain.
+  // (To be used only on the first textframe in the chain.)
+  nsTextFrame* FindContinuationForOffset(int32_t aOffset);
 
  protected:
   virtual ~nsTextFrame();
@@ -1010,6 +1011,10 @@ class nsTextFrame : public nsIFrame {
 
   void ClearMetrics(ReflowOutput& aMetrics);
 
+  // Return pointer to an array of all frames in the continuation chain, or
+  // null if we're too short of memory.
+  nsTArray<nsTextFrame*>* GetContinuations();
+
   // Clear any cached continuations array; this should be called whenever the
   // chain is modified.
   void ClearCachedContinuations() {