Bug 1725555 - patch 2 - Enable the primary nsTextFrame to provide, and cache, an array of all the continuations in the chain. r=emilio

This allows us to binary-search the continuations from nsRange::CollectClientRectsAndText,
instead of linear-searching the linked list for every range we need to look up.

Depends on D122998

Differential Revision: https://phabricator.services.mozilla.com/D122999

dom/base/nsRange.cpp

@@ -2647,10 +2647,40 @@ static nsresult GetPartialTextRect(RectCallback* aCallback,
   if (textFrame) {
     nsIFrame* relativeTo =
         nsLayoutUtils::GetContainingBlockForClientRect(textFrame);
-    for (nsTextFrame* f = textFrame; f;
+
-         f = static_cast<nsTextFrame*>(f->GetNextContinuation())) {
+    // 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())) {
       int32_t fstart = f->GetContentOffset(), fend = f->GetContentEnd();
-      if (fend <= aStartOffset || fstart >= aEndOffset) continue;
+      if (fend <= aStartOffset) {
+        continue;
+      }
+      if (fstart >= aEndOffset) {
+        break;
+      }
 
       // Calculate the text content offsets we'll need if text is requested.
       int32_t textContentStart = fstart;

layout/generic/nsTextFrame.cpp

@@ -4384,6 +4384,35 @@ void nsTextFrame::DestroyFrom(nsIFrame* aDestructRoot,
   nsIFrame::DestroyFrom(aDestructRoot, aPostDestroyData);
 }
 
+nsTArray<nsTextFrame*>* nsTextFrame::GetContinuations() {
+  MOZ_ASSERT(NS_IsMainThread());
+  // Only for use on the primary frame, which has no prev-continuation.
+  MOZ_ASSERT(!GetPrevContinuation());
+  if (!mNextContinuation) {
+    return nullptr;
+  }
+  if (mHasContinuationsProperty) {
+    return GetProperty(ContinuationsProperty());
+  }
+  size_t count = 0;
+  for (nsIFrame* f = this; f; f = f->GetNextContinuation()) {
+    ++count;
+  }
+  auto* continuations = new nsTArray<nsTextFrame*>;
+  if (continuations->SetCapacity(count, fallible)) {
+    for (nsTextFrame* f = this; f;
+         f = static_cast<nsTextFrame*>(f->GetNextContinuation())) {
+      continuations->AppendElement(f);
+    }
+  } else {
+    delete continuations;
+    continuations = nullptr;
+  }
+  AddProperty(ContinuationsProperty(), continuations);
+  mHasContinuationsProperty = true;
+  return continuations;
+}
+
 class nsContinuingTextFrame final : public nsTextFrame {
  public:
   NS_DECL_FRAMEARENA_HELPERS(nsContinuingTextFrame)
@@ -4410,10 +4439,16 @@ class nsContinuingTextFrame final : public nsTextFrame {
     nsTextFrame* prevFirst = mFirstContinuation;
     if (mPrevContinuation) {
       mFirstContinuation = mPrevContinuation->FirstContinuation();
+      if (mFirstContinuation) {
+        mFirstContinuation->ClearCachedContinuations();
+      }
     } else {
       mFirstContinuation = nullptr;
     }
     if (mFirstContinuation != prevFirst) {
+      if (prevFirst) {
+        prevFirst->ClearCachedContinuations();
+      }
       auto* f = static_cast<nsContinuingTextFrame*>(mNextContinuation);
       while (f) {
         f->mFirstContinuation = mFirstContinuation;
@@ -4438,10 +4473,16 @@ class nsContinuingTextFrame final : public nsTextFrame {
     nsTextFrame* prevFirst = mFirstContinuation;
     if (mPrevContinuation) {
       mFirstContinuation = mPrevContinuation->FirstContinuation();
+      if (mFirstContinuation) {
+        mFirstContinuation->ClearCachedContinuations();
+      }
     } else {
       mFirstContinuation = nullptr;
     }
     if (mFirstContinuation != prevFirst) {
+      if (prevFirst) {
+        prevFirst->ClearCachedContinuations();
+      }
       auto* f = static_cast<nsContinuingTextFrame*>(mNextContinuation);
       while (f) {
         f->mFirstContinuation = mFirstContinuation;
@@ -4457,6 +4498,8 @@ class nsContinuingTextFrame final : public nsTextFrame {
     return mFirstContinuation;
   };
 
+  nsTArray<nsTextFrame*>* GetContinuations() final { return nullptr; }
+
   void AddInlineMinISize(gfxContext* aRenderingContext,
                          InlineMinISizeData* aData) final;
   void AddInlinePrefISize(gfxContext* aRenderingContext,
@@ -9121,6 +9164,12 @@ void nsTextFrame::ReflowText(nsLineLayout& aLineLayout, nscoord aAvailableWidth,
   RemoveStateBits(TEXT_REFLOW_FLAGS | TEXT_WHITESPACE_FLAGS);
   mReflowRequestedForCharDataChange = false;
   RemoveProperty(WebRenderTextBounds());
+
+  // Discard cached continuations array that will be invalidated by the reflow.
+  if (nsTextFrame* first = FirstContinuation()) {
+    first->ClearCachedContinuations();
+  }
+
   // Temporarily map all possible content while we construct our new textrun.
   // so that when doing reflow our styles prevail over any part of the
   // textrun we look at. Note that next-in-flows may be mapping the same

layout/generic/nsTextFrame.h

@@ -214,6 +214,9 @@ class nsTextFrame : public nsIFrame {
   // nsQueryFrame
   NS_DECL_QUERYFRAME
 
+  NS_DECLARE_FRAME_PROPERTY_DELETABLE(ContinuationsProperty,
+                                      nsTArray<nsTextFrame*>)
+
   // nsIFrame
   void BuildDisplayList(nsDisplayListBuilder* aBuilder,
                         const nsDisplayListSet& aLists) final;
@@ -781,6 +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();
+
  protected:
   virtual ~nsTextFrame();
 
@@ -815,6 +823,9 @@ class nsTextFrame : public nsIFrame {
   };
   mutable SelectionState mIsSelected;
 
+  // Whether a cached continuations array is present.
+  bool mHasContinuationsProperty = false;
+
   /**
    * Return true if the frame is part of a Selection.
    * Helper method to implement the public IsSelected() API.
@@ -999,6 +1010,16 @@ class nsTextFrame : public nsIFrame {
 
   void ClearMetrics(ReflowOutput& aMetrics);
 
+  // Clear any cached continuations array; this should be called whenever the
+  // chain is modified.
+  void ClearCachedContinuations() {
+    MOZ_ASSERT(NS_IsMainThread());
+    if (mHasContinuationsProperty) {
+      RemoveProperty(ContinuationsProperty());
+      mHasContinuationsProperty = false;
+    }
+  }
+
   /**
    * UpdateIteratorFromOffset() updates the iterator from a given offset.
    * Also, aInOffset may be updated to cluster start if aInOffset isn't
@@ -1010,8 +1031,6 @@ class nsTextFrame : public nsIFrame {
 
   nsPoint GetPointFromIterator(const gfxSkipCharsIterator& aIter,
                                PropertyProvider& aProperties);
-
- public:
 };
 
 MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(nsTextFrame::TrimmedOffsetFlags)