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Fix rounding of negative numbers #825

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Fix rounding of negative numbers #825

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57 changes: 57 additions & 0 deletions tests/YGRoundingFunctionTest.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,13 @@ TEST(YogaTest, rounding_value) {
ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(5.999999, 2.0, false, false));
ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(5.999999, 2.0, true, false));
ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(5.999999, 2.0, false, true));
// Same tests for negative numbers
ASSERT_FLOAT_EQ(-6.0, YGRoundValueToPixelGrid(-6.000001, 2.0, false, false));
ASSERT_FLOAT_EQ(-6.0, YGRoundValueToPixelGrid(-6.000001, 2.0, true, false));
ASSERT_FLOAT_EQ(-6.0, YGRoundValueToPixelGrid(-6.000001, 2.0, false, true));
ASSERT_FLOAT_EQ(-6.0, YGRoundValueToPixelGrid(-5.999999, 2.0, false, false));
ASSERT_FLOAT_EQ(-6.0, YGRoundValueToPixelGrid(-5.999999, 2.0, true, false));
ASSERT_FLOAT_EQ(-6.0, YGRoundValueToPixelGrid(-5.999999, 2.0, false, true));

// Test that numbers with fraction are rounded correctly accounting for ceil/floor flags
ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(6.01, 2.0, false, false));
Expand All @@ -25,4 +32,54 @@ TEST(YogaTest, rounding_value) {
ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(5.99, 2.0, false, false));
ASSERT_FLOAT_EQ(6.0, YGRoundValueToPixelGrid(5.99, 2.0, true, false));
ASSERT_FLOAT_EQ(5.5, YGRoundValueToPixelGrid(5.99, 2.0, false, true));
// Same tests for negative numbers
ASSERT_FLOAT_EQ(-6.0, YGRoundValueToPixelGrid(-6.01, 2.0, false, false));
ASSERT_FLOAT_EQ(-6.0, YGRoundValueToPixelGrid(-6.01, 2.0, true, false));
ASSERT_FLOAT_EQ(-6.5, YGRoundValueToPixelGrid(-6.01, 2.0, false, true));
ASSERT_FLOAT_EQ(-6.0, YGRoundValueToPixelGrid(-5.99, 2.0, false, false));
ASSERT_FLOAT_EQ(-5.5, YGRoundValueToPixelGrid(-5.99, 2.0, true, false));
ASSERT_FLOAT_EQ(-6.0, YGRoundValueToPixelGrid(-5.99, 2.0, false, true));
}

static YGSize measureText(
YGNodeRef node,
float width,
YGMeasureMode widthMode,
float height,
YGMeasureMode heightMode
) {
return (YGSize){
.width = 10,
.height = 10
};
}

// Regression test for https://github.com/facebook/yoga/issues/824
TEST(YogaTest, consistent_rounding_during_repeated_layouts) {
const YGConfigRef config = YGConfigNew();
YGConfigSetPointScaleFactor(config, 2);

const YGNodeRef root = YGNodeNewWithConfig(config);
YGNodeStyleSetMargin(root, YGEdgeTop, -1.49);
YGNodeStyleSetWidth(root, 500);
YGNodeStyleSetHeight(root, 500);

const YGNodeRef node0 = YGNodeNewWithConfig(config);
YGNodeInsertChild(root, node0, 0);

const YGNodeRef node1 = YGNodeNewWithConfig(config);
YGNodeSetMeasureFunc(node1, measureText);
YGNodeInsertChild(node0, node1, 0);

for (int i = 0; i < 5; i++) {
// Dirty the tree so YGRoundToPixelGrid runs again
YGNodeStyleSetMargin(root, YGEdgeLeft, i + 1);

YGNodeCalculateLayout(root, YGUndefined, YGUndefined, YGDirectionLTR);
ASSERT_FLOAT_EQ(10, YGNodeLayoutGetHeight(node1));
}

YGNodeFreeRecursive(root);

YGConfigFree(config);
}
19 changes: 19 additions & 0 deletions yoga/Yoga.cpp
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Expand Up @@ -3608,7 +3608,26 @@ float YGRoundValueToPixelGrid(
const bool forceCeil,
const bool forceFloor) {
float scaledValue = value * pointScaleFactor;
// We want to calculate `fractial` such that `floor(scaledValue) = scaledValue - fractial`.
float fractial = fmodf(scaledValue, 1.0f);
if (fractial < 0) {
// This branch is for handling negative numbers for `value`.
//
// Regarding `floor` and `ceil`. Note that for a number x, `floor(x) <= x <= ceil(x)` even for
// negative numbers. Here are a couple of examples:
// - x = 2.2: floor( 2.2) = 2, ceil( 2.2) = 3
// - x = -2.2: floor(-2.2) = -3, ceil(-2.2) = -2
//
// Regarding `fmodf`. For fractional negative numbers, `fmodf` returns a negative
// number. For example, `fmodf(-2.2) = -0.2`. However, we want `fractial` to be the
// number such that subtracting it from `value` will give us `floor(value)`. In the
// case of negative numbers, adding 1 to `fmodf(value)` gives us this. Let's continue
// the example from above:
// - fractial = fmodf(-2.2) = -0.2
// - Add 1 to the fraction: fractial2 = fractial + 1 = -0.2 + 1 = 0.8
// - Finding the `floor`: -2.2 - fractial2 = -2.2 - 0.8 = -3
++fractial;
}
if (YGFloatsEqual(fractial, 0)) {
// First we check if the value is already rounded
scaledValue = scaledValue - fractial;
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