Bug 1820988 - Handle separator characters in canvas2d TextReplaceWhitespaceCharacters, to avoid a second preprocessing of the string in ProcessText. r=gfx-reviewers,aosmond

This avoids an extra string copy/scan in ProcessText, by including the block/segment
separators it cares about in the preprocessing that's already being done to normalize
whitespace characters by the caller.

Depends on D171986

Differential Revision: https://phabricator.services.mozilla.com/D171987

dom/canvas/CanvasRenderingContext2D.cpp

@@ -3845,10 +3845,13 @@ void CanvasRenderingContext2D::GetFontKerning(nsAString& aFontKerning) {
  * with U+0020 SPACE. The whitespace characters are defined as U+0020 SPACE,
  * U+0009 CHARACTER TABULATION (tab), U+000A LINE FEED (LF), U+000B LINE
  * TABULATION, U+000C FORM FEED (FF), and U+000D CARRIAGE RETURN (CR).
+ * We also replace characters with Bidi type Segment Separator or Block
+ * Separator.
  * @param str The string whose whitespace characters to replace.
  */
 static inline void TextReplaceWhitespaceCharacters(nsAutoString& aStr) {
-  aStr.ReplaceChar(u"\x09\x0A\x0B\x0C\x0D", char16_t(' '));
+  aStr.ReplaceChar(u"\x09\x0A\x0B\x0C\x0D\x1C\x1D\x1E\x1F\x85\x2029",
+                   char16_t(' '));
 }
 
 void CanvasRenderingContext2D::FillText(const nsAString& aText, double aX,

layout/base/nsBidiPresUtils.cpp

@@ -2144,11 +2144,12 @@ nsresult nsBidiPresUtils::ProcessText(const char16_t* aText, size_t aLength,
   NS_ASSERTION((aPosResolve == nullptr) != (aPosResolveCount > 0),
                "Incorrect aPosResolve / aPosResolveCount arguments");
 
-  nsAutoString textBuffer(aText, aLength);
-  textBuffer.ReplaceChar(kSeparators, kSpace);
-  const char16_t* text = textBuffer.get();
+  // Caller should have already replaced any separators in the original text
+  // with <space> characters.
+  MOZ_ASSERT(nsDependentString(aText, aLength).FindCharInSet(kSeparators) ==
+             kNotFound);
 
-  if (aBidiEngine->SetParagraph(Span(text, aLength), aBaseLevel).isErr()) {
+  if (aBidiEngine->SetParagraph(Span(aText, aLength), aBaseLevel).isErr()) {
     return NS_ERROR_FAILURE;
   }
 
@@ -2209,7 +2210,7 @@ nsresult nsBidiPresUtils::ProcessText(const char16_t* aText, size_t aLength,
      */
 
     if (dir == intl::BidiDirection::RTL) {
-      aprocessor.SetText(text + start, subRunLength, intl::BidiDirection::RTL);
+      aprocessor.SetText(aText + start, subRunLength, intl::BidiDirection::RTL);
       width = aprocessor.GetWidth();
       xOffset += width;
       xEndRun = xOffset;
@@ -2218,11 +2219,10 @@ nsresult nsBidiPresUtils::ProcessText(const char16_t* aText, size_t aLength,
     while (subRunCount > 0) {
       // CalculateBidiClass can increment subRunCount if the run
       // contains mixed character types
-      CalculateBidiClass(text, lineOffset, typeLimit, subRunLimit, subRunLength,
-                         subRunCount, bidiClass, prevClass);
+      CalculateBidiClass(aText, lineOffset, typeLimit, subRunLimit,
+                         subRunLength, subRunCount, bidiClass, prevClass);
 
-      nsAutoString runVisualText;
-      runVisualText.Assign(text + start, subRunLength);
+      nsAutoString runVisualText(aText + start, subRunLength);
       if (aPresContext) {
         FormatUnicodeText(aPresContext, runVisualText.BeginWriting(),
                           subRunLength, bidiClass);
@@ -2308,14 +2308,14 @@ nsresult nsBidiPresUtils::ProcessText(const char16_t* aText, size_t aLength,
                   visualStart +
                   (subRunLength - (posResolve->logicalIndex + 1 - start));
               // Skipping to the "left part".
-              visualLeftPart = text + posResolve->logicalIndex + 1;
+              visualLeftPart = aText + posResolve->logicalIndex + 1;
               // Skipping to the right side of the current character
               visualRightSide = visualLeftPart - 1;
             } else {
               posResolve->visualIndex =
                   visualStart + (posResolve->logicalIndex - start);
               // Skipping to the "left part".
-              visualLeftPart = text + start;
+              visualLeftPart = aText + start;
               // In LTR mode this is the same as visualLeftPart
               visualRightSide = visualLeftPart;
             }