Bug 683952. Speed up iterating over the continuations of the frame when scrolling to it. r=roc

layout/base/nsPresShell.cpp

@@ -4044,13 +4044,19 @@ PresShell::ScrollToAnchor()
  * we should include the top of the line in the added rectangle
  * @param aRect [inout] rect into which its bounds should be unioned
  * @param aHaveRect [inout] whether aRect contains data yet
+ * @param aPrevBlock [inout] the block aLines is a line iterator for
+ * @param aLines [inout] the line iterator we're using
+ * @param aCurLine [inout] the line to start looking from in this iterator
  */
 static void
 AccumulateFrameBounds(nsIFrame* aContainerFrame,
                       nsIFrame* aFrame,
                       PRBool aUseWholeLineHeightForInlines,
                       nsRect& aRect,
-                      PRBool& aHaveRect)
+                      PRBool& aHaveRect,
+                      nsIFrame*& aPrevBlock,
+                      nsAutoLineIterator& aLines,
+                      PRInt32& aCurLine)
 {
   nsRect frameBounds = aFrame->GetRect() +
     aFrame->GetParent()->GetOffsetTo(aContainerFrame);
@@ -4073,17 +4079,22 @@ AccumulateFrameBounds(nsIFrame* aContainerFrame,
         f &&
         frameType == nsGkAtoms::blockFrame) {
       // find the line containing aFrame and increase the top of |offset|.
-      nsAutoLineIterator lines = f->GetLineIterator();
-      if (lines) {
-        PRInt32 index = lines->FindLineContaining(prevFrame);
+      if (f != aPrevBlock) {
+        aLines = f->GetLineIterator();
+        aPrevBlock = f;
+        aCurLine = 0;
+      }
+      if (aLines) {
+        PRInt32 index = aLines->FindLineContaining(prevFrame, aCurLine);
         if (index >= 0) {
+          aCurLine = index;
           nsIFrame *trash1;
           PRInt32 trash2;
           nsRect lineBounds;
           PRUint32 trash3;
 
-          if (NS_SUCCEEDED(lines->GetLine(index, &trash1, &trash2,
-                                          lineBounds, &trash3))) {
+          if (NS_SUCCEEDED(aLines->GetLine(index, &trash1, &trash2,
+                                           lineBounds, &trash3))) {
             lineBounds += f->GetOffsetTo(aContainerFrame);
             if (lineBounds.y < frameBounds.y) {
               frameBounds.height = frameBounds.YMost() - lineBounds.y;
@@ -4286,9 +4297,16 @@ PresShell::DoScrollContentIntoView(nsIContent* aContent,
   nsRect frameBounds;
   PRBool haveRect = PR_FALSE;
   PRBool useWholeLineHeightForInlines = aVPercent != NS_PRESSHELL_SCROLL_ANYWHERE;
+  // Reuse the same line iterator across calls to AccumulateFrameBounds.  We set
+  // it every time we detect a new block (stored in prevBlock).
+  nsIFrame* prevBlock = nsnull;
+  nsAutoLineIterator lines;
+  // The last line we found a continuation on in |lines|.  We assume that later
+  // continuations cannot come on earlier lines.
+  PRInt32 curLine = 0;
   do {
     AccumulateFrameBounds(container, frame, useWholeLineHeightForInlines,
-                          frameBounds, haveRect);
+                          frameBounds, haveRect, prevBlock, lines, curLine);
   } while ((frame = frame->GetNextContinuation()));
 
   ScrollFrameRectIntoView(container, frameBounds, aVPercent, aHPercent,

layout/generic/nsILineIterator.h

@@ -104,9 +104,12 @@ public:
 
   /**
    * Given a frame that's a child of the block, find which line its on
-   * and return that line index. Returns -1 if the frame cannot be found.
+   * and return that line index, as long as it's at least as big as
+   * aStartLine.  Returns -1 if the frame cannot be found on lines
+   * starting with aStartLine.
    */
-  virtual PRInt32 FindLineContaining(nsIFrame* aFrame) = 0;
+  virtual PRInt32 FindLineContaining(nsIFrame* aFrame,
+                                     PRInt32 aStartLine = 0) = 0;
 
   // Given a line number and an X coordinate, find the frame on the
   // line that is nearest to the X coordinate. The

layout/generic/nsLineBox.cpp

@@ -626,15 +626,16 @@ nsLineIterator::GetLine(PRInt32 aLineNumber,
 }
 
 PRInt32
-nsLineIterator::FindLineContaining(nsIFrame* aFrame)
+nsLineIterator::FindLineContaining(nsIFrame* aFrame, PRInt32 aStartLine)
 {
-  nsLineBox* line = mLines[0];
-  PRInt32 lineNumber = 0;
+  NS_PRECONDITION(aStartLine <= mNumLines, "Bogus line numbers");
+  PRInt32 lineNumber = aStartLine;
   while (lineNumber != mNumLines) {
+    nsLineBox* line = mLines[lineNumber];
     if (line->Contains(aFrame)) {
       return lineNumber;
     }
-    line = mLines[++lineNumber];
+    ++lineNumber;
   }
   return -1;
 }

layout/generic/nsLineBox.h

@@ -1581,7 +1581,7 @@ public:
                      PRInt32* aNumFramesOnLine,
                      nsRect& aLineBounds,
                      PRUint32* aLineFlags);
-  virtual PRInt32 FindLineContaining(nsIFrame* aFrame);
+  virtual PRInt32 FindLineContaining(nsIFrame* aFrame, PRInt32 aStartLine = 0);
   NS_IMETHOD FindFrameAt(PRInt32 aLineNumber,
                          nscoord aX,
                          nsIFrame** aFrameFound,

layout/tables/nsTableRowGroupFrame.cpp

@@ -1706,14 +1706,16 @@ nsTableRowGroupFrame::GetLine(PRInt32    aLineNumber,
 }
   
 PRInt32
-nsTableRowGroupFrame::FindLineContaining(nsIFrame* aFrame)
+nsTableRowGroupFrame::FindLineContaining(nsIFrame* aFrame, PRInt32 aStartLine)
 {
   NS_ENSURE_ARG_POINTER(aFrame);
   
   nsTableRowFrame *rowFrame = do_QueryFrame(aFrame);
   NS_ASSERTION(rowFrame, "RowGroup contains a frame that is not a row");
 
-  return rowFrame->GetRowIndex() - GetStartRowIndex();
+  PRInt32 rowIndexInGroup = rowFrame->GetRowIndex() - GetStartRowIndex();
+
+  return rowIndexInGroup >= aStartLine ? rowIndexInGroup : -1;
 }
 
 #ifdef IBMBIDI

layout/tables/nsTableRowGroupFrame.h

@@ -258,10 +258,12 @@ public:
   
   /** Given a frame that's a child of the rowgroup, find which line its on.
     * @param aFrame       - frame, should be a row
+    * @param aStartLine   - minimal index to return
     * @return               row index relative to the row group if this a row
-    *                       frame. -1 if the frame cannot be found.
+    *                       frame and the index is at least aStartLine.
+    *                       -1 if the frame cannot be found.
     */
-  virtual PRInt32 FindLineContaining(nsIFrame* aFrame);
+  virtual PRInt32 FindLineContaining(nsIFrame* aFrame, PRInt32 aStartLine = 0);
 
   /** Find the orginating cell frame on a row that is the nearest to the
     * coordinate X.