Font's fast code path doesn't handle partial runs correctly when kerning or ligatures are enabled

https://bugs.webkit.org/show_bug.cgi?id=100050

Reviewed by Darin Adler.

Renamed m_characterIndex to m_characterIndexOfGlyph and gave it an inline size of 10,
which covers around 66% of all cases. The rest of the cases are now preallocated to the
upper limit which is length of the original TextRun.

* platform/graphics/FontFastPath.cpp:
(WebCore::Font::getGlyphsAndAdvancesForSimpleText):
(WebCore::Font::selectionRectForSimpleText):
(WebCore::Font::offsetForPositionForSimpleText):
* platform/graphics/WidthIterator.cpp:
(WebCore::WidthIterator::WidthIterator):
(WebCore::WidthIterator::advanceInternal):
* platform/graphics/WidthIterator.h:

Change-Id: I253195dc5fc07b4c9d0bb4947cd07d86f054a265
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154674 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>

3 files changed, 12 insertions, 9 deletions

diff --git a/Source/WebCore/platform/graphics/FontFastPath.cpp b/Source/WebCore/platform/graphics/FontFastPath.cpp
index 22ce7f57e..d1553ea3f 100644
--- a/Source/WebCore/platform/graphics/FontFastPath.cpp
+++ b/Source/WebCore/platform/graphics/FontFastPath.cpp
@@ -335,13 +335,13 @@ float Font::getGlyphsAndAdvancesForSimpleText(const TextRun& run, int from, int
     float totalWidth = it.m_runWidthSoFar;
     float beforeWidth = 0;
     int glyphPos = 0;
-    for (; glyphPos < localGlyphBuffer.size() && it.m_characterIndex[glyphPos] < from; ++glyphPos)
+    for (; glyphPos < localGlyphBuffer.size() && it.m_characterIndexOfGlyph[glyphPos] < from; ++glyphPos)
         beforeWidth += localGlyphBuffer.advanceAt(glyphPos);
     int glyphFrom = glyphPos;
 
     float afterWidth = totalWidth;
     glyphPos = localGlyphBuffer.size() - 1;
-    for (; glyphPos >= glyphFrom && it.m_characterIndex[glyphPos] >= to; --glyphPos)
+    for (; glyphPos >= glyphFrom && it.m_characterIndexOfGlyph[glyphPos] >= to; --glyphPos)
         afterWidth -= localGlyphBuffer.advanceAt(glyphPos);
     int glyphTo = glyphPos + 1;
 
@@ -494,13 +494,13 @@ FloatRect Font::selectionRectForSimpleText(const TextRun& run, const FloatPoint&
     float totalWidth = it.m_runWidthSoFar;
     float beforeWidth = 0;
     int glyphPos = 0;
-    for (; glyphPos < glyphBuffer.size() && it.m_characterIndex[glyphPos] < from; ++glyphPos)
+    for (; glyphPos < glyphBuffer.size() && it.m_characterIndexOfGlyph[glyphPos] < from; ++glyphPos)
         beforeWidth += glyphBuffer.advanceAt(glyphPos);
     int glyphFrom = glyphPos;
 
     float afterWidth = totalWidth;
     glyphPos = glyphBuffer.size() - 1;
-    for (; glyphPos >= glyphFrom && it.m_characterIndex[glyphPos] >= to; --glyphPos)
+    for (; glyphPos >= glyphFrom && it.m_characterIndexOfGlyph[glyphPos] >= to; --glyphPos)
         afterWidth -= glyphBuffer.advanceAt(glyphPos);
 
     // Using roundf() rather than ceilf() for the right edge as a compromise to ensure correct caret positioning.
@@ -525,7 +525,7 @@ int Font::offsetForPositionForSimpleText(const TextRun& run, float x, bool inclu
                 characterOffset = run.length();
                 break;
             }
-            characterOffset = it.m_characterIndex[glyphPosition];
+            characterOffset = it.m_characterIndexOfGlyph[glyphPosition];
             float glyphWidth = glyphBuffer.advanceAt(glyphPosition);
             if (includePartialGlyphs) {
                 if (currentX - glyphWidth / 2.0f <= x)
@@ -543,7 +543,7 @@ int Font::offsetForPositionForSimpleText(const TextRun& run, float x, bool inclu
                 characterOffset = run.length();
                 break;
             }
-            characterOffset = it.m_characterIndex[glyphPosition];
+            characterOffset = it.m_characterIndexOfGlyph[glyphPosition];
             float glyphWidth = glyphBuffer.advanceAt(glyphPosition);
             if (includePartialGlyphs) {
                 if (currentX + glyphWidth / 2.0f >= x)
diff --git a/Source/WebCore/platform/graphics/WidthIterator.cpp b/Source/WebCore/platform/graphics/WidthIterator.cpp
index 1fb1d9b40..7a1698d19 100644
--- a/Source/WebCore/platform/graphics/WidthIterator.cpp
+++ b/Source/WebCore/platform/graphics/WidthIterator.cpp
@@ -67,6 +67,8 @@ WidthIterator::WidthIterator(const Font* font, const TextRun& run, HashSet<const
         else
             m_expansionPerOpportunity = m_expansion / expansionOpportunityCount;
     }
+    // Character-index will end up the same or slightly shorter than m_run, so if we reserve that much it will never need to resize.
+    m_characterIndexOfGlyph.reserveInitialCapacity(m_run.length());
 }
 
 GlyphData WidthIterator::glyphDataForCharacter(UChar32 character, bool mirror, int currentCharacter, unsigned& advanceLength)
@@ -226,7 +228,7 @@ inline unsigned WidthIterator::advanceInternal(TextIterator& textIterator, Glyph
                         if (glyphBuffer) {
                             if (glyphBuffer->isEmpty()) {
                                 glyphBuffer->add(fontData->spaceGlyph(), fontData, expansionAtThisOpportunity);
-                                m_characterIndex.append(currentCharacterIndex);
+                                m_characterIndexOfGlyph.append(currentCharacterIndex);
                             } else
                                 glyphBuffer->expandLastAdvance(expansionAtThisOpportunity);
                         }
@@ -295,7 +297,7 @@ inline unsigned WidthIterator::advanceInternal(TextIterator& textIterator, Glyph
 
         if (glyphBuffer) {
             glyphBuffer->add(glyph, fontData, (rtl ? oldWidth + lastRoundingWidth : width));
-            m_characterIndex.append(currentCharacterIndex);
+            m_characterIndexOfGlyph.append(currentCharacterIndex);
         }
 
         lastRoundingWidth = width - oldWidth;
diff --git a/Source/WebCore/platform/graphics/WidthIterator.h b/Source/WebCore/platform/graphics/WidthIterator.h
index 43007e80d..8aa26782c 100644
--- a/Source/WebCore/platform/graphics/WidthIterator.h
+++ b/Source/WebCore/platform/graphics/WidthIterator.h
@@ -82,7 +82,8 @@ public:
     float m_expansionPerOpportunity;
     bool m_isAfterExpansion;
     float m_finalRoundingWidth;
-    Vector<int> m_characterIndex;
+    // An inline capacity of 10 catches around 2/3 of the cases. To catch 90% we would need 32.
+    Vector<int, 10> m_characterIndexOfGlyph;
 
 #if ENABLE(SVG_FONTS)
     String m_lastGlyphName;