in yoga/Yoga.cpp [3622:3671]
YOGA_EXPORT float YGRoundValueToPixelGrid(
const double value,
const double pointScaleFactor,
const bool forceCeil,
const bool forceFloor) {
double scaledValue = value * pointScaleFactor;
// We want to calculate `fractial` such that `floor(scaledValue) = scaledValue
// - fractial`.
double fractial = fmod(scaledValue, 1.0);
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 (YGDoubleEqual(fractial, 0)) {
// First we check if the value is already rounded
scaledValue = scaledValue - fractial;
} else if (YGDoubleEqual(fractial, 1.0)) {
scaledValue = scaledValue - fractial + 1.0;
} else if (forceCeil) {
// Next we check if we need to use forced rounding
scaledValue = scaledValue - fractial + 1.0;
} else if (forceFloor) {
scaledValue = scaledValue - fractial;
} else {
// Finally we just round the value
scaledValue = scaledValue - fractial +
(!YGDoubleIsUndefined(fractial) &&
(fractial > 0.5 || YGDoubleEqual(fractial, 0.5))
? 1.0
: 0.0);
}
return (YGDoubleIsUndefined(scaledValue) ||
YGDoubleIsUndefined(pointScaleFactor))
? YGUndefined
: (float) (scaledValue / pointScaleFactor);
}