Changeset 63357 in webkit

Timestamp:

Jul 14, 2010, 2:41:02 PM (15 years ago)

Author:

mitz@apple.com

Message:

<rdar://problem/7759909> Certain text runs measure 1 pixel wider when measured as a whole than when measured piecewise
​https://bugs.webkit.org/show_bug.cgi?id=42279

Reviewed by Simon Fraser.

No test because the issue cannot be reproduced with standard fonts.

Word- and run-rounding works by advancing ahead to the nearest integral width. As the total
width accumulated becomes large, the float type’s low precision results in accumulated rounding
error, sometimes crossing an integer. Consequently, word-rounding makes different decisions when
measuring a multi-word run than when measuring its words individually. To work around this,
word- and run-rounding are applied only to the width accumulated since the last rounding
character.

• platform/graphics/WidthIterator.cpp:

(WebCore::WidthIterator::advance):

• platform/graphics/mac/ComplexTextController.cpp:

(WebCore::ComplexTextController::adjustGlyphsAndAdvances):

Location:

trunk/WebCore

Files:

• ChangeLog (modified) (1 diff)
• platform/graphics/WidthIterator.cpp (modified) (4 diffs)
• platform/graphics/mac/ComplexTextController.cpp (modified) (5 diffs)

trunk/WebCore/ChangeLog

@@ +1 @@
+2010-07-14  Dan Bernstein  <mitz@apple.com>
+
+        Reviewed by Simon Fraser.
+
+        <rdar://problem/7759909> Certain text runs measure 1 pixel wider when measured as a whole than when measured piecewise
+        https://bugs.webkit.org/show_bug.cgi?id=42279
+
+        No test because the issue cannot be reproduced with standard fonts.
+
+        Word- and run-rounding works by advancing ahead to the nearest integral width. As the total
+        width accumulated becomes large, the float type’s low precision results in accumulated rounding
+        error, sometimes crossing an integer. Consequently, word-rounding makes different decisions when
+        measuring a multi-word run than when measuring its words individually. To work around this,
+        word- and run-rounding are applied only to the width accumulated since the last rounding
+        character.
+
+        * platform/graphics/WidthIterator.cpp:
+        (WebCore::WidthIterator::advance):
+        * platform/graphics/mac/ComplexTextController.cpp:
+        (WebCore::ComplexTextController::adjustGlyphsAndAdvances):
+
 2010-07-14  Tony Gentilcore  <tonyg@chromium.org>
 

trunk/WebCore/platform/graphics/WidthIterator.cpp

@@ -85 +85 @@
     bool hasExtraSpacing = (m_font->letterSpacing() || m_font->wordSpacing() || m_padding) && !m_run.spacingDisabled();
 
-    float runWidthSoFar = m_runWidthSoFar;
+    float widthSinceLastRounding = m_runWidthSoFar;
+    m_runWidthSoFar = floorf(m_runWidthSoFar);
+    widthSinceLastRounding -= m_runWidthSoFar;
+
     float lastRoundingWidth = m_finalRoundingWidth;
     FloatRect bounds;
@@ -132 +135 @@
         if (c == '\t' && m_run.allowTabs()) {
             float tabWidth = m_font->tabWidth();
-            width = tabWidth - fmodf(m_run.xPos() + runWidthSoFar, tabWidth);
+            width = tabWidth - fmodf(m_run.xPos() + m_runWidthSoFar + widthSinceLastRounding, tabWidth);
         } else {
             width = fontData->widthForGlyph(glyph);
@@ -217 +220 @@
         if ((m_run.applyWordRounding() && currentCharacter < m_run.length() && Font::isRoundingHackCharacter(*cp))
                 || (m_run.applyRunRounding() && currentCharacter >= m_end)) {
-            float totalWidth = runWidthSoFar + width;
-            width += ceilf(totalWidth) - totalWidth;
-        }
-
-        runWidthSoFar += width;
+            float totalWidth = widthSinceLastRounding + width;
+            widthSinceLastRounding = ceilf(totalWidth);
+            width += widthSinceLastRounding - totalWidth;
+            m_runWidthSoFar += widthSinceLastRounding;
+            widthSinceLastRounding = 0;
+        } else
+            widthSinceLastRounding += width;
 
         if (glyphBuffer)
@@ -236 +241 @@
 
     m_currentCharacter = currentCharacter;
-    m_runWidthSoFar = runWidthSoFar;
+    m_runWidthSoFar += widthSinceLastRounding;
     m_finalRoundingWidth = lastRoundingWidth;
 }

trunk/WebCore/platform/graphics/mac/ComplexTextController.cpp

@@ -432 +432 @@
 void ComplexTextController::adjustGlyphsAndAdvances()
 {
+    CGFloat widthSinceLastRounding = 0;
     size_t runCount = m_complexTextRuns.size();
     for (size_t r = 0; r < runCount; ++r) {
@@ -475 +476 @@
             if (ch == '\t' && m_run.allowTabs()) {
                 float tabWidth = m_font.tabWidth();
-                advance.width = tabWidth - fmodf(m_run.xPos() + m_totalWidth, tabWidth);
+                advance.width = tabWidth - fmodf(m_run.xPos() + m_totalWidth + widthSinceLastRounding, tabWidth);
             } else if (ch == zeroWidthSpace || Font::treatAsZeroWidthSpace(ch) && !treatAsSpace) {
                 advance.width = 0;
@@ -533 +534 @@
             // width so that the total run width will be on an integer boundary.
             if (m_run.applyWordRounding() && !lastGlyph && Font::isRoundingHackCharacter(nextCh) || m_run.applyRunRounding() && lastGlyph) {
-                CGFloat totalWidth = m_totalWidth + advance.width;
-                CGFloat extraWidth = ceilCGFloat(totalWidth) - totalWidth;
+                CGFloat totalWidth = widthSinceLastRounding + advance.width;
+                widthSinceLastRounding = ceilCGFloat(totalWidth);
+                CGFloat extraWidth = widthSinceLastRounding - totalWidth;
                 if (m_run.ltr())
                     advance.width += extraWidth;
                 else {
-                    m_totalWidth += extraWidth;
                     if (m_lastRoundingGlyph)
                         m_adjustedAdvances[m_lastRoundingGlyph - 1].width += extraWidth;
@@ -545 +546 @@
                     m_lastRoundingGlyph = m_adjustedAdvances.size() + 1;
                 }
-            }
-
-            m_totalWidth += advance.width;
+                m_totalWidth += widthSinceLastRounding;
+                widthSinceLastRounding = 0;
+            } else
+                widthSinceLastRounding += advance.width;
+
             advance.height *= -1;
             m_adjustedAdvances.append(advance);
@@ -566 +569 @@
             complexTextRun.setIsNonMonotonic();
     }
+    m_totalWidth += widthSinceLastRounding;
 }