Fix MathML fraction bar not painted when thickness equals width

Ahmad-S792 · Ahmad Saleem · commit a787642717c3 · 2026-02-22T23:44:58.000-08:00
https://bugs.webkit.org/show_bug.cgi?id=308440 rdar://170934351 Reviewed by Frédéric Wang. GraphicsContext::drawLine() misidentifies horizontal lines as vertical when stroke thickness equals the distance between endpoints. This causes the fraction bar to not render when FractionRuleThickness produces a thickness equal to the bar width. Replace drawLine() with fillRect() to draw the fraction bar as an explicit rectangle, avoiding the heuristic entirely. * LayoutTests/TestExpectations: Progressions * Source/WebCore/rendering/mathml/RenderMathMLFraction.cpp: (WebCore::RenderMathMLFraction::paint): Canonical link: https://commits.webkit.org/308025@main
diff --git a/LayoutTests/TestExpectations b/LayoutTests/TestExpectations
@@ -1995,10 +1995,7 @@ imported/w3c/web-platform-tests/html/browsers/windows/nested-browsing-contexts/f
 
 # These MathML WPT tests fail.
 webkit.org/b/180013 mathml/non-core/lengths-2.html [ ImageOnlyFailure ]
-webkit.org/b/194952 imported/w3c/web-platform-tests/mathml/presentation-markup/fractions/frac-bar-001.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/mathml/presentation-markup/direction/direction-overall-003.html [ ImageOnlyFailure ]
-imported/w3c/web-platform-tests/mathml/presentation-markup/fractions/frac-bar-002.html [ ImageOnlyFailure ]
-imported/w3c/web-platform-tests/mathml/presentation-markup/fractions/frac-default-padding.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/mathml/presentation-markup/operators/embellished-op-1-2.html [ ImageOnlyFailure Pass ]
 imported/w3c/web-platform-tests/mathml/presentation-markup/operators/embellished-op-1-3.html [ ImageOnlyFailure Pass ]
 imported/w3c/web-platform-tests/mathml/presentation-markup/operators/embellished-op-1-4.html [ ImageOnlyFailure Pass ]
@@ -2051,7 +2048,6 @@ imported/w3c/web-platform-tests/mathml/relations/css-styling/clip.html [ ImageOn
 imported/w3c/web-platform-tests/mathml/relations/css-styling/presentational-hints-001.html [ ImageOnlyFailure Pass ]
 imported/w3c/web-platform-tests/mathml/relations/css-styling/transform.html [ ImageOnlyFailure ]
 
-imported/w3c/web-platform-tests/mathml/presentation-markup/fractions/frac-bar-003.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/mathml/presentation-markup/operators/mo-lspace-rspace-2.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/mathml/presentation-markup/operators/mo-movablelimits-and-embellished-operator.html [ ImageOnlyFailure ]
 imported/w3c/web-platform-tests/mathml/presentation-markup/operators/op-dict-8.html [ ImageOnlyFailure ]
diff --git a/Source/WebCore/rendering/mathml/RenderMathMLFraction.cpp b/Source/WebCore/rendering/mathml/RenderMathMLFraction.cpp
@@ -293,16 +293,18 @@ void RenderMathMLFraction::paint(PaintInfo& info, const LayoutPoint& paintOffset
         return;
 
     LayoutUnit borderAndPaddingLeft = writingMode().isBidiLTR() ? borderAndPaddingStart() : borderAndPaddingEnd();
-    auto adjustedPaintOffset = roundPointToDevicePixels(paintOffset + location() + LayoutPoint(borderAndPaddingLeft, borderAndPaddingBefore() + fractionAscent() - mathAxisHeight()), document().deviceScaleFactor());
+    LayoutUnit barX = borderAndPaddingLeft;
+    LayoutUnit barY = borderAndPaddingBefore() + fractionAscent() - mathAxisHeight() - thickness / 2;
+    LayoutUnit barWidth = logicalWidth() - borderAndPaddingLogicalWidth();
+
+    auto barOrigin = roundPointToDevicePixels(paintOffset + location() + LayoutPoint(barX, barY), document().deviceScaleFactor());
+    auto barEnd = roundPointToDevicePixels(paintOffset + location() + LayoutPoint(barX + barWidth, barY + thickness), document().deviceScaleFactor());
 
     GraphicsContextStateSaver stateSaver(info.context());
 
-    info.context().setStrokeThickness(thickness);
-    info.context().setStrokeStyle(StrokeStyle::SolidStroke);
-    info.context().setStrokeColor(style().visitedDependentColorApplyingColorFilter());
     // MathML Core says the fraction bar takes the full width of the content box.
-    auto endPoint = roundPointToDevicePixels({ adjustedPaintOffset.x() + logicalWidth() - borderAndPaddingLogicalWidth(), adjustedPaintOffset.y() }, document().deviceScaleFactor());
-    info.context().drawLine(adjustedPaintOffset, endPoint);
+    info.context().setFillColor(style().visitedDependentColorApplyingColorFilter());
+    info.context().fillRect({ barOrigin, barEnd });
 }
 
 std::optional<LayoutUnit> RenderMathMLFraction::firstLineBaseline() const
