Optimize SVGTextQuery's character offset ligature adjustment query

Source/core/rendering/svg/SVGTextQuery.cpp

 /*
  * Copyright (C) Research In Motion Limited 2010-2012. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 20 matching lines @@
 
 namespace WebCore {
 
 // Base structure for callback user data
 struct SVGTextQuery::Data {
     Data()
         : isVerticalText(false)
         , processedCharacters(0)
         , textRenderer(0)
         , textBox(0)
+        , ligatureAdjustmentLastStartPositionQuery(-1)
+        , ligatureAdjustmentLastEndPositionQuery(-1)
+        , ligatureAdjustmentLastStartPositionResult(-1)
+        , ligatureAdjustmentLastEndPositionResult(-1)
     {
     }
 
+    void invalidateLigatureAdjustmentCache()
+    {
+        ligatureAdjustmentLastStartPositionQuery = ligatureAdjustmentLastEndPositionQuery = -1;
+        ligatureAdjustmentLastStartPositionResult = ligatureAdjustmentLastEndPositionResult = -1;
+    }
+
     bool isVerticalText;
     unsigned processedCharacters;
     RenderSVGInlineText* textRenderer;
     const SVGInlineTextBox* textBox;
+    // Ligature adjustment cache.
+    int ligatureAdjustmentLastStartPositionQuery;
+    int ligatureAdjustmentLastEndPositionQuery;
+    int ligatureAdjustmentLastStartPositionResult;
+    int ligatureAdjustmentLastEndPositionResult;
 };
 
 static inline InlineFlowBox* flowBoxForRenderer(RenderObject* renderer)
 {
     if (!renderer)
         return 0;
 
     if (renderer->isRenderBlock()) {
         // If we're given a block element, it has to be a RenderSVGText.
         ASSERT(renderer->isSVGText());
@@ skipping 65 matching lines @@
         unsigned fragmentCount = fragments.size();
         for (unsigned i = 0; i < fragmentCount; ++i) {
             const SVGTextFragment& fragment = fragments.at(i);
             if ((this->*fragmentCallback)(queryData, fragment))
                 return true;
 
             processedCharacters += fragment.length;
         }
 
         queryData->processedCharacters = processedCharacters;
+        queryData->invalidateLigatureAdjustmentCache();
     }
 
     return false;
 }
 
 bool SVGTextQuery::mapStartEndPositionsIntoFragmentCoordinates(Data* queryData, const SVGTextFragment& fragment, int& startPosition, int& endPosition) const
 {
     // Reuse the same logic used for text selection & painting, to map our query start/length into start/endPositions of the current text fragment.
     startPosition -= queryData->processedCharacters;
     endPosition -= queryData->processedCharacters;
 
     startPosition = max(0, startPosition);
 
     if (startPosition >= endPosition)
         return false;
 
     modifyStartEndPositionsRespectingLigatures(queryData, startPosition, endPosition);
     if (!queryData->textBox->mapStartEndPositionsIntoFragmentCoordinates(fragment, startPosition, endPosition))
         return false;
 
     ASSERT(startPosition < endPosition);
     return true;
 }
 
 void SVGTextQuery::modifyStartEndPositionsRespectingLigatures(Data* queryData, int& startPosition, int& endPosition) const
 {
+    if (queryData->ligatureAdjustmentLastStartPositionQuery == startPosition && queryData->ligatureAdjustmentLastEndPositionQuery == endPosition) {
+        startPosition = queryData->ligatureAdjustmentLastStartPositionResult;
+        endPosition = queryData->ligatureAdjustmentLastEndPositionResult;
+        return;
+    }
+
+    queryData->ligatureAdjustmentLastStartPositionQuery = startPosition;
+    queryData->ligatureAdjustmentLastEndPositionQuery = endPosition;
+
     SVGTextLayoutAttributes* layoutAttributes = queryData->textRenderer->layoutAttributes();
     Vector<SVGTextMetrics>& textMetricsValues = layoutAttributes->textMetricsValues();
     unsigned boxStart = queryData->textBox->start();
     unsigned boxLength = queryData->textBox->len();
 
     unsigned textMetricsOffset = 0;
     unsigned textMetricsSize = textMetricsValues.size();
 
     unsigned positionOffset = 0;
     unsigned positionSize = layoutAttributes->context()->textLength();
@@ skipping 36 matching lines @@
             }
         }
 
         if (!alterStartPosition && !alterEndPosition)
             break;
 
         lastPositionOffset = positionOffset;
         positionOffset += metrics.length();
     }
 
-    if (!alterStartPosition && !alterEndPosition)
-        return;
+    if (alterStartPosition || alterEndPosition) {
+        if (lastPositionOffset != -1 && lastPositionOffset - positionOffset > 1) {
+            if (alterStartPosition && startPosition > lastPositionOffset && startPosition < static_cast<int>(positionOffset))
+                startPosition = lastPositionOffset;
 
-    if (lastPositionOffset != -1 && lastPositionOffset - positionOffset > 1) {
-        if (alterStartPosition && startPosition > lastPositionOffset && startPosition < static_cast<int>(positionOffset))
-            startPosition = lastPositionOffset;
+            if (alterEndPosition && endPosition > lastPositionOffset && endPosition < static_cast<int>(positionOffset))
+                endPosition = positionOffset;
+        }
+    }
 
-        if (alterEndPosition && endPosition > lastPositionOffset && endPosition < static_cast<int>(positionOffset))
-            endPosition = positionOffset;
-    }
+    queryData->ligatureAdjustmentLastStartPositionResult = startPosition;
+    queryData->ligatureAdjustmentLastEndPositionResult = endPosition;
 }
 
 // numberOfCharacters() implementation
 bool SVGTextQuery::numberOfCharactersCallback(Data*, const SVGTextFragment&) const
 {
     // no-op
     return false;
 }
 
 unsigned SVGTextQuery::numberOfCharacters() const
@@ skipping 306 matching lines @@
         return -1;
 
     CharacterNumberAtPositionData data(position);
     if (!executeQuery(&data, &SVGTextQuery::characterNumberAtPositionCallback))
         return -1;
 
     return data.processedCharacters;
 }
 
 }