Changeset 213008 in webkit

Timestamp:

Feb 25, 2017, 2:18:23 PM (9 years ago)

Author:

Alan Bujtas

Message:

Text might wrap when its preferred logical width is used for sizing the containing block.
​https://bugs.webkit.org/show_bug.cgi?id=168864
<rdar://problem/30690734>

Reviewed by Antti Koivisto.

Source/WebCore:

In certain cases we end up measuring a text run in 2 different ways.

1. preferred width computation -> slow path FontCascade::width()
2. line breaking logic -> fast path FontCascade::widthForSimpleText()

FontCascade::width() and ::widthForSimpleText() might return different results for the same run even when
the individual glyph widths are measured to be the same. It's because they run diffrent set of
arithmetics on the float values and for certain values these arithmetics produce different results due to the floating point
precision.
Since RenderText::computePreferredLogicalWidths() currently forces us to use the slow path
(to retrieve fontfallback and glyph overflow information) the only alternative solution is to turn off the fast path
for all runs that have been already measured using the slow path (which would be just wasteful).

Test: fast/text/fast-run-width-vs-slow-run-width.html

• platform/graphics/FontCascade.cpp:

(WebCore::FontCascade::widthForSimpleText): Mimics WidthIterator::applyFontTransforms. Use the same set of arithmetics here.

LayoutTests:

• fast/text/fast-run-width-vs-slow-run-width-expected.html: Added.
• fast/text/fast-run-width-vs-slow-run-width.html: Added.

Location:

trunk

Files:

• LayoutTests/ChangeLog (modified) (1 diff)
• LayoutTests/fast/text/fast-run-width-vs-slow-run-width-expected.html (added)
• LayoutTests/fast/text/fast-run-width-vs-slow-run-width.html (added)
• Source/WebCore/ChangeLog (modified) (1 diff)
• Source/WebCore/platform/graphics/FontCascade.cpp (modified) (2 diffs)

trunk/LayoutTests/ChangeLog

@@ +1 @@
+2017-02-25  Zalan Bujtas <zalan@apple.com>
+
+        Text might wrap when its preferred logical width is used for sizing the containing block.
+        https://bugs.webkit.org/show_bug.cgi?id=168864
+        <rdar://problem/30690734>
+
+        Reviewed by Antti Koivisto.
+
+        * fast/text/fast-run-width-vs-slow-run-width-expected.html: Added.
+        * fast/text/fast-run-width-vs-slow-run-width.html: Added.
+
 2017-02-25  Michael Catanzaro  <mcatanzaro@igalia.com>
 

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2017-02-25  Zalan Bujtas  <zalan@apple.com>
+
+        Text might wrap when its preferred logical width is used for sizing the containing block.
+        https://bugs.webkit.org/show_bug.cgi?id=168864
+        <rdar://problem/30690734>
+
+        Reviewed by Antti Koivisto.
+
+        In certain cases we end up measuring a text run in 2 different ways.
+        1. preferred width computation -> slow path FontCascade::width() 
+        2. line breaking logic -> fast path FontCascade::widthForSimpleText()
+ 
+        FontCascade::width() and ::widthForSimpleText() might return different results for the same run even when
+        the individual glyph widths are measured to be the same. It's because they run diffrent set of
+        arithmetics on the float values and for certain values these arithmetics produce different results due to the floating point
+        precision.
+        Since RenderText::computePreferredLogicalWidths() currently forces us to use the slow path
+        (to retrieve fontfallback and glyph overflow information) the only alternative solution is to turn off the fast path
+        for all runs that have been already measured using the slow path (which would be just wasteful).
+
+        Test: fast/text/fast-run-width-vs-slow-run-width.html
+
+        * platform/graphics/FontCascade.cpp:
+        (WebCore::FontCascade::widthForSimpleText): Mimics WidthIterator::applyFontTransforms. Use the same set of arithmetics here.  
+
 2017-02-24  Simon Fraser  <simon.fraser@apple.com>
 

trunk/Source/WebCore/platform/graphics/FontCascade.cpp

@@ -383 +383 @@
 float FontCascade::widthForSimpleText(StringView text) const
 {
+    if (text.isNull() || text.isEmpty())
+        return 0;
     ASSERT(codePath(TextRun(text)) != FontCascade::Complex);
     float* cacheEntry = m_fonts->widthCache().add(text, std::numeric_limits<float>::quiet_NaN());
@@ -410 +412 @@
     if (hasKerningOrLigatures) {
         font.applyTransforms(&glyphs[0], &advances[0], glyphs.size(), enableKerning(), requiresShaping());
-        runWidth = 0;
+        // This is needed only to match the result of the slow path. Same glyph widths but different floating point arithmentics can
+        // produce different run width.
+        float runWidthDifferenceWithTransformApplied = -runWidth;
         for (auto& advance : advances)
-            runWidth += advance.width();
+            runWidthDifferenceWithTransformApplied += advance.width();
+        runWidth += runWidthDifferenceWithTransformApplied;
     }