Add tab characters support in complex path

Source/platform/fonts/shaping/CachingWordShapeIterator.h

Index: Source/platform/fonts/shaping/CachingWordShapeIterator.h
diff --git a/Source/platform/fonts/shaping/CachingWordShapeIterator.h b/Source/platform/fonts/shaping/CachingWordShapeIterator.h
index 2321d81c85b47ea976ea3c5a79578111c3cab5fe..dbaafbc886f7109313ae61ee5ab6c3f345aae669 100644
--- a/Source/platform/fonts/shaping/CachingWordShapeIterator.h
+++ b/Source/platform/fonts/shaping/CachingWordShapeIterator.h
@@ -38,7 +38,8 @@ class CachingWordShapeIterator {
 public:
     CachingWordShapeIterator(ShapeCache* cache, const TextRun& run,
         const Font* font)
-        : m_shapeCache(cache), m_textRun(run), m_font(font), m_startIndex(0)
+        : m_shapeCache(cache), m_textRun(run), m_font(font)
+        , m_widthSoFar(0), m_startIndex(0)
     {
         ASSERT(font);
         const FontDescription& fontDescription = font->fontDescription();
@@ -60,6 +61,8 @@ public:
     bool next(RefPtr<ShapeResult>* wordResult)
     {
         if (!m_shapeByWord) {
+            if (UNLIKELY(m_textRun.allowTabs()))
+                return nextForAllowTabs(wordResult);
             if (m_startIndex)
                 return false;
             *wordResult = shapeWord(m_textRun, m_font);
@@ -76,16 +79,10 @@ public:
                 return true;
             }
 
-            for (unsigned i = m_startIndex; ; i++) {
-                if (i == length || m_textRun[i] == spaceCharacter) {
-                    TextRun wordRun = m_textRun.subRun(m_startIndex,
-                        i - m_startIndex);
-                    *wordResult = shapeWord(wordRun, m_font);
-                    m_startIndex = i;
-                    return true;
-                }
-            }
+            *wordResult = shapeWordUntilCharacter(spaceCharacter);
+            return true;

[eae, 2015/08/10 17:24:07]

Shouldn't this be "return *wordResult != nullptr;"?

[kojii, 2015/08/11 07:22:21]

Done. The fix was moved to nextUntilCharacterOrTab() below so that compiler can
generate jmp instead of call.

Also applied the same fix for spaceCharacter case (moved to nextWord() below.)
These fixes change the behavior of next() slightly, I hope to be more correct.

         }
+
         return false;
     }
 
@@ -109,9 +106,46 @@ private:
         return shapeResult.release();
     }
 
+    PassRefPtr<ShapeResult> shapeWordUntilCharacter(UChar delimiter)
+    {
+        unsigned length = m_textRun.length();
+        ASSERT(m_startIndex < length);
+        for (unsigned i = m_startIndex + 1;; i++) {
+            if (i == length || m_textRun[i] == delimiter) {
+                TextRun wordRun = m_textRun.subRun(m_startIndex,
+                    i - m_startIndex);
+                m_startIndex = i;
+                return shapeWord(wordRun, m_font);
+            }
+        }

[eae, 2015/08/10 17:24:07]

Missing "return nullptr"?

[kojii, 2015/08/11 07:22:20]

The loop exits only with "return", so it's not necessary. I added
ASSERT_NOT_REACHED() for clarification, but compiler claimed that the code is
not reachable.

+    }
+
+    bool nextForAllowTabs(RefPtr<ShapeResult>* wordResult)
+    {
+        unsigned length = m_textRun.length();
+        if (m_startIndex >= length)
+            return false;
+
+        if (UNLIKELY(m_textRun[m_startIndex] == tabulationCharacter)) {
+            for (unsigned i = m_startIndex + 1;; i++) {
+                if (i == length || m_textRun[i] != tabulationCharacter) {
+                    *wordResult = ShapeResult::createForTabulationCharacters(
+                        m_font, m_textRun, m_widthSoFar, i - m_startIndex);
+                    m_startIndex = i;
+                    break;
+                }
+            }
+        } else {
+            *wordResult = shapeWordUntilCharacter(tabulationCharacter);

[eae, 2015/08/10 17:24:07]

Shouldn't this still segment on space? I.e. shape until either a space or a
tabulation character is encountered?

[kojii, 2015/08/11 07:22:21]

Good point, we need to do that if we want to cache words in allowTabs(). I
wasn't trying to do so, but after trying, it wasn't as complicated as thought.

PS13 adds this capability. Now we need to check allowTabs() on every next()
call. Is this ok? If you don't think the cost is worth the value, I can revert
to PS12 (which reflects your other comments.)

It turns out that <select> implies allowTabs(), so I needed to rebaseline for
sub-pixel changes caused by the segmenting. Image diff below:
https://storage.googleapis.com/chromium-layout-test-archives/linux_blink_rel/...

+        }
+        m_widthSoFar += (*wordResult)->width();
+        return true;
+    }
+
     ShapeCache* m_shapeCache;
     const TextRun& m_textRun;
     const Font* m_font;
+    float m_widthSoFar; // Used only when allowTabs()
     unsigned m_startIndex : 30;
     unsigned m_wordResultCachable : 1;
     unsigned m_shapeByWord : 1;