Optimize SVGTextQuery's character offset ligature adjustment query

Source/core/rendering/svg/SVGTextQuery.cpp

Index: Source/core/rendering/svg/SVGTextQuery.cpp
diff --git a/Source/core/rendering/svg/SVGTextQuery.cpp b/Source/core/rendering/svg/SVGTextQuery.cpp
index f5ead0d43661f2ec0f636f48021b511100a0b748..93d8ea4b7c02b30b31a971abe4ecca7a8b6211f5 100644
--- a/Source/core/rendering/svg/SVGTextQuery.cpp
+++ b/Source/core/rendering/svg/SVGTextQuery.cpp
@@ -38,13 +38,28 @@ struct SVGTextQuery::Data {
         , 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)
@@ -130,6 +145,7 @@ bool SVGTextQuery::executeQuery(Data* queryData, ProcessTextFragmentCallback fra
         }
 
         queryData->processedCharacters = processedCharacters;
+        queryData->invalidateLigatureAdjustmentCache();
     }
 
     return false;
@@ -156,6 +172,15 @@ bool SVGTextQuery::mapStartEndPositionsIntoFragmentCoordinates(Data* queryData,
 
 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();
@@ -212,16 +237,18 @@ void SVGTextQuery::modifyStartEndPositionsRespectingLigatures(Data* queryData, i
         positionOffset += metrics.length();
     }
 
-    if (!alterStartPosition && !alterEndPosition)
-        return;
-
-    if (lastPositionOffset != -1 && lastPositionOffset - positionOffset > 1) {
-        if (alterStartPosition && startPosition > lastPositionOffset && startPosition < static_cast<int>(positionOffset))
-            startPosition = lastPositionOffset;
+    if (alterStartPosition || alterEndPosition) {
+        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