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Fix layout bug caused by floating point rounding error #1860

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Fix layout bug caused by floating point rounding error #1860

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ee425cb
failing test
matthieugicquel Aug 26, 2025
410092c
fix that works but is probably not the right one
matthieugicquel Aug 26, 2025
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24 changes: 24 additions & 0 deletions tests/YGRoundingFunctionTest.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -181,3 +181,27 @@ TEST(YogaTest, raw_layout_dimensions) {

YGConfigFree(config);
}

TEST(YogaTest, roundLayoutResultsToPixelGrid_height_rounding_up) {
YGConfigRef config = YGConfigNew();
YGConfigSetPointScaleFactor(config, 3);

YGNodeRef node = YGNodeNewWithConfig(config);
YGNodeStyleSetPositionType(node, YGPositionTypeAbsolute);

// These are values extracted from a debugging session in a real iOS app
YGNodeStyleSetPosition(node, YGEdgeLeft, 38.333333969116211);
YGNodeStyleSetPosition(node, YGEdgeTop, 1970.3333333432674);
YGNodeStyleSetWidth(node, 339.66665649414063);
YGNodeStyleSetHeight(node, 96);
YGNodeSetNodeType(node, YGNodeTypeText);

YGNodeCalculateLayout(node, YGUndefined, YGUndefined, YGDirectionLTR);

// If this value is anything less than 96, iOS will not wrap the text to a 4th line
ASSERT_FLOAT_EQ(YGNodeLayoutGetHeight(node), 96.0f);

YGNodeFreeRecursive(node);

YGConfigFree(config);
}
26 changes: 17 additions & 9 deletions yoga/algorithm/PixelGrid.cpp
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Expand Up @@ -116,15 +116,23 @@ void roundLayoutResultsToPixelGrid(
roundValueToPixelGrid(
absoluteNodeLeft, pointScaleFactor, false, textRounding));

node->getLayout().setDimension(
Dimension::Height,
roundValueToPixelGrid(
absoluteNodeBottom,
pointScaleFactor,
(textRounding && hasFractionalHeight),
(textRounding && !hasFractionalHeight)) -
roundValueToPixelGrid(
absoluteNodeTop, pointScaleFactor, false, textRounding));
// -- Height --
const float roundedBottom = roundValueToPixelGrid(
absoluteNodeBottom,
pointScaleFactor,
(textRounding && hasFractionalHeight),
(textRounding && !hasFractionalHeight));
const float roundedTop = roundValueToPixelGrid(
absoluteNodeTop, pointScaleFactor, false, textRounding);

const float roundedHeight = roundValueToPixelGrid(
roundedBottom - roundedTop,
pointScaleFactor,
false, // Don't force ceil for height calculation
false // Don't force floor for height calculation
);

node->getLayout().setDimension(Dimension::Height, roundedHeight);
}

for (yoga::Node* child : node->getChildren()) {
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