Bug 1114297 - Improve performance of nsTreeBodyFrame::AdjustForCellText for very long strings; r=smontagu

layout/base/nsLayoutUtils.cpp

@@ -5121,6 +5121,28 @@ nsLayoutUtils::AppUnitWidthOfStringBidi(const char16_t* aString,
                                              aContext);
 }
 
+bool
+nsLayoutUtils::StringWidthIsGreaterThan(const nsString& aString,
+                                        nsFontMetrics& aFontMetrics,
+                                        nsRenderingContext& aContext,
+                                        nscoord aWidth)
+{
+  const char16_t *string = aString.get();
+  uint32_t length = aString.Length();
+  uint32_t maxChunkLength = GetMaxChunkLength(aFontMetrics);
+  nscoord width = 0;
+  while (length > 0) {
+    int32_t len = FindSafeLength(string, length, maxChunkLength);
+    width += aFontMetrics.GetWidth(string, len, &aContext);
+    if (width > aWidth) {
+      return true;
+    }
+    length -= len;
+    string += len;
+  }
+  return false;
+}
+
 nsBoundingMetrics
 nsLayoutUtils::AppUnitBoundsOfString(const char16_t* aString,
                                      uint32_t aLength,

layout/base/nsLayoutUtils.h

@@ -1486,6 +1486,11 @@ public:
                                           nsFontMetrics& aFontMetrics,
                                           nsRenderingContext& aContext);
 
+  static bool StringWidthIsGreaterThan(const nsString& aString,
+                                       nsFontMetrics& aFontMetrics,
+                                       nsRenderingContext& aContext,
+                                       nscoord aWidth);
+
   static nsBoundingMetrics AppUnitBoundsOfString(const char16_t* aString,
                                                  uint32_t aLength,
                                                  nsFontMetrics& aFontMetrics,

layout/xul/tree/nsTreeBodyFrame.cpp

@@ -1319,15 +1319,16 @@ nsTreeBodyFrame::AdjustForCellText(nsAutoString& aText,
 {
   NS_PRECONDITION(aColumn && aColumn->GetFrame(), "invalid column passed");
 
-  nscoord width = nsLayoutUtils::AppUnitWidthOfStringBidi(aText, this,
-                                                          aFontMetrics,
-                                                          aRenderingContext);
   nscoord maxWidth = aTextRect.width;
+  bool widthIsGreater = nsLayoutUtils::StringWidthIsGreaterThan(aText,
+                                                                aFontMetrics,
+                                                                aRenderingContext,
+                                                                maxWidth);
 
   if (aColumn->Overflow()) {
     DebugOnly<nsresult> rv;
     nsTreeColumn* nextColumn = aColumn->GetNext();
-    while (nextColumn && width > maxWidth) {
+    while (nextColumn && widthIsGreater) {
       while (nextColumn) {
         nscoord width;
         rv = nextColumn->GetWidthInTwips(this, &width);
@@ -1351,6 +1352,10 @@ nsTreeBodyFrame::AdjustForCellText(nsAutoString& aText,
           NS_ASSERTION(NS_SUCCEEDED(rv), "nextColumn is invalid");
 
           maxWidth += width;
+          widthIsGreater = nsLayoutUtils::StringWidthIsGreaterThan(aText,
+                                                                   aFontMetrics,
+                                                                   aRenderingContext,
+                                                                   maxWidth);
 
           nextColumn = nextColumn->GetNext();
         }
@@ -1361,7 +1366,8 @@ nsTreeBodyFrame::AdjustForCellText(nsAutoString& aText,
     }
   }
 
-  if (width > maxWidth) {
+  nscoord width;
+  if (widthIsGreater) {
     // See if the width is even smaller than the ellipsis
     // If so, clear the text completely.
     const nsDependentString& kEllipsis = nsContentUtils::GetLocalizedEllipsis();
@@ -1458,11 +1464,11 @@ nsTreeBodyFrame::AdjustForCellText(nsAutoString& aText,
         break;
       }
     }
-
-    width = nsLayoutUtils::AppUnitWidthOfStringBidi(aText, this, aFontMetrics,
-                                                    aRenderingContext);
   }
 
+  width = nsLayoutUtils::AppUnitWidthOfStringBidi(aText, this, aFontMetrics,
+                                                  aRenderingContext);
+
   switch (aColumn->GetTextAlignment()) {
     case NS_STYLE_TEXT_ALIGN_RIGHT: {
       aTextRect.x += aTextRect.width - width;