Prevent to measure the whole word when break-all

third_party/WebKit/Source/core/layout/line/BreakingContextInlineHeaders.h

Index: third_party/WebKit/Source/core/layout/line/BreakingContextInlineHeaders.h
diff --git a/third_party/WebKit/Source/core/layout/line/BreakingContextInlineHeaders.h b/third_party/WebKit/Source/core/layout/line/BreakingContextInlineHeaders.h
index c123a226e44773465d4dc62328234378a4bce34f..42ffdcb47383e6017fa1a6526cf90139c1d65ea4 100644
--- a/third_party/WebKit/Source/core/layout/line/BreakingContextInlineHeaders.h
+++ b/third_party/WebKit/Source/core/layout/line/BreakingContextInlineHeaders.h
@@ -116,6 +116,9 @@ public:
 
 private:
     void skipTrailingWhitespace(InlineIterator&, const LineInfo&);
+    bool shouldMidWordBreak(UChar, LineLayoutText, const Font&,
+        float& charWidth, float& widthFromLastBreakingOpportunity,
+        bool breakAll, int& nextBreakablePositionForBreakAll);
     bool rewindToMidWordBreak(WordMeasurement&, int end, float width);
     bool rewindToFirstMidWordBreak(LineLayoutText, const ComputedStyle&, const Font&, bool breakAll, WordMeasurement&);
     bool rewindToMidWordBreak(LineLayoutText, const ComputedStyle&, const Font&, bool breakAll, WordMeasurement&);
@@ -542,6 +545,36 @@ ALWAYS_INLINE float textWidth(LineLayoutText text, unsigned from, unsigned len,
     return font.width(run, fallbackFonts, glyphBounds);
 }
 
+ALWAYS_INLINE bool BreakingContext::shouldMidWordBreak(
+    UChar c, LineLayoutText layoutText, const Font& font,
+    float& charWidth, float& widthFromLastBreakingOpportunity,
+    bool breakAll, int& nextBreakablePositionForBreakAll)
+{
+    // For breakWords/breakAll, we need to measure up to normal break
+    // opportunity and then rewindToMidWordBreak() because ligatures/kerning can
+    // shorten the width as we add more characters.
+    // However, doing so can hit the performance when a "word" is really long,
+    // such as minimized JS, because the next line will re-shape the rest of the
+    // word in the current architecture.
+    // This function is a heuristic optimization to stop at 2em overflow.
+    float overflowAllowance = 2 * font.getFontDescription().computedSize();
+
+    widthFromLastBreakingOpportunity += charWidth;
+    bool midWordBreakIsBeforeSurrogatePair = U16_IS_LEAD(c) && m_current.offset() + 1 < layoutText.textLength() && U16_IS_TRAIL(layoutText.uncheckedCharacterAt(m_current.offset() + 1));
+    charWidth = textWidth(layoutText, m_current.offset(), midWordBreakIsBeforeSurrogatePair ? 2 : 1, font, m_width.committedWidth() + widthFromLastBreakingOpportunity, m_collapseWhiteSpace);
+    if (m_width.committedWidth() + widthFromLastBreakingOpportunity + charWidth <= m_width.availableWidth() + overflowAllowance)
+        return false;
+

[kojii, 2016/07/05 11:37:58]

Up to this point in this function is just a move from handleText(). The
following logic is the additional one.

+    // breakAll has different break opportunities. Ensure we break only at
+    // breakAll allows to break.
+    if (breakAll &&
+        !m_layoutTextInfo.m_lineBreakIterator.isBreakable(m_current.offset(), nextBreakablePositionForBreakAll, LineBreakType::BreakAll)) {
+        return false;
+    }
+
+    return true;
+}
+
 ALWAYS_INLINE int lastBreakablePositionForBreakAll(LineLayoutText text,
     const ComputedStyle& style, int start, int end)
 {
@@ -715,6 +748,7 @@ inline bool BreakingContext::handleText(WordMeasurements& wordMeasurements, bool
     // rewindToMidWordBreak() finds the mid-word break point.
     LineBreakType lineBreakType = keepAll ? LineBreakType::KeepAll : LineBreakType::Normal;
     bool canBreakMidWord = breakAll || breakWords;
+    int nextBreakablePositionForBreakAll = -1;
 
     if (layoutText.isWordBreak()) {
         m_width.commit();
@@ -756,16 +790,8 @@ inline bool BreakingContext::handleText(WordMeasurements& wordMeasurements, bool
         bool applyWordSpacing = false;
 
         // Determine if we should try breaking in the middle of a word.
-        if (breakWords && !midWordBreak && !U16_IS_TRAIL(c)) {
-            widthFromLastBreakingOpportunity += charWidth;
-            bool midWordBreakIsBeforeSurrogatePair = U16_IS_LEAD(c) && m_current.offset() + 1 < layoutText.textLength() && U16_IS_TRAIL(layoutText.uncheckedCharacterAt(m_current.offset() + 1));
-            charWidth = textWidth(layoutText, m_current.offset(), midWordBreakIsBeforeSurrogatePair ? 2 : 1, font, m_width.committedWidth() + widthFromLastBreakingOpportunity, m_collapseWhiteSpace);
-            // Measure up to 2em overflow since ligatures/kerning can shorten
-            // the width as we add more characters. rewindToMidWordBreak() can
-            // measure the accurate mid-word break point then.
-            midWordBreak = m_width.committedWidth() + widthFromLastBreakingOpportunity + charWidth > m_width.availableWidth()
-                + 2 * font.getFontDescription().computedSize();
-        }
+        if (canBreakMidWord && !midWordBreak && !U16_IS_TRAIL(c))
+            midWordBreak = shouldMidWordBreak(c, layoutText, font, charWidth, widthFromLastBreakingOpportunity, breakAll, nextBreakablePositionForBreakAll);
 
         // Determine if we are in the whitespace between words.
         int nextBreakablePosition = m_current.nextBreakablePosition();
@@ -827,10 +853,6 @@ inline bool BreakingContext::handleText(WordMeasurements& wordMeasurements, bool
             m_appliedStartWidth = true;
         }
 
-        // If we haven't hit a breakable position yet and already don't fit on the line try to move below any floats.
-        if (!m_width.committedWidth() && m_autoWrap && !m_width.fitsOnLine() && !widthMeasurementAtLastBreakOpportunity)
-            m_width.fitBelowFloats(m_lineInfo.isFirstLine());
-
         midWordBreak = false;
         if (!m_width.fitsOnLine()) {
             if (canBreakMidWord) {
@@ -854,6 +876,15 @@ inline bool BreakingContext::handleText(WordMeasurements& wordMeasurements, bool
             }
         }
 
+        // If we haven't hit a breakable position yet and already don't fit on the line try to move below any floats.
+        if (!m_width.committedWidth() && m_autoWrap && !m_width.fitsOnLine() && !widthMeasurementAtLastBreakOpportunity) {
+            float availableWidthBefore = m_width.availableWidth();
+            m_width.fitBelowFloats(m_lineInfo.isFirstLine());
+            // If availableWidth changes by moving the line below floats, needs to measure midWordBreak again.
+            if (midWordBreak && availableWidthBefore != m_width.availableWidth())
+                midWordBreak = false;
+        }

[kojii, 2016/07/05 11:37:58]

Doing this before rewindToMidWordBreak was the previous fix, but it was
incorrect. The new fix is to revert to do it after, but reset midWordBreak if
availableWidth was changed by floats, so that we loop again to recompute the new
break opportunity.

With this fix applied, word-break-all-wrap-with-floats.html fails without this
additional fix.

+
         // If there is a soft-break available at this whitespace position then take it.
         applyWordSpacing = wordSpacing && m_currentCharacterIsSpace;
         if (canBreakAtWhitespace(breakWords, wordMeasurement, stoppedIgnoringSpaces, charWidth, hyphenated, disableSoftHyphen, hyphenWidth, betweenWords, midWordBreak, canBreakMidWord, previousCharacterIsSpace, lastWidthMeasurement, layoutText, font, applyWordSpacing, wordSpacing))