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https://github.com/facebook/react-native.git
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J.T. Yim
4eec47344e
Summary: Changelog: [Internal] Include FlexLayout C++ source to ReactCommons Reviewed By: d16r, NickGerleman Differential Revision: D38716145 fbshipit-source-id: 0ca2ab040e72168f2f1b479609b6cda2787eba66
70 lines
2.4 KiB
C++
70 lines
2.4 KiB
C++
/*
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* Copyright (c) Meta Platforms, Inc. and affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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#include "Rounding.h"
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#include <cmath>
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#include "Utils.h"
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namespace facebook {
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namespace flexlayout {
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namespace algo {
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using namespace facebook::flexlayout::utils;
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auto RoundValueToPixelGrid(
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const double value,
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const double pointScaleFactor,
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const bool forceCeil,
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const bool forceFloor) -> float {
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double scaledValue = value * pointScaleFactor;
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if (isUndefined(scaledValue) || isUndefined(pointScaleFactor)) {
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return NAN;
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}
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// We want to calculate `fractial` such that `floor(scaledValue) = scaledValue
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// - fractial`.
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double fractial = fmod(scaledValue, 1.0f);
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if (fractial < 0) {
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// This branch is for handling negative numbers for `value`.
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//
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// Regarding `floor` and `ceil`. Note that for a number x, `floor(x) <= x <=
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// ceil(x)` even for negative numbers. Here are a couple of examples:
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// - x = 2.2: floor( 2.2) = 2, ceil( 2.2) = 3
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// - x = -2.2: floor(-2.2) = -3, ceil(-2.2) = -2
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//
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// Regarding `fmodf`. For fractional negative numbers, `fmodf` returns a
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// negative number. For example, `fmodf(-2.2) = -0.2`. However, we want
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// `fractial` to be the number such that subtracting it from `value` will
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// give us `floor(value)`. In the case of negative numbers, adding 1 to
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// `fmodf(value)` gives us this. Let's continue the example from above:
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// - fractial = fmodf(-2.2) = -0.2
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// - Add 1 to the fraction: fractial2 = fractial + 1 = -0.2 + 1 = 0.8
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// - Finding the `floor`: -2.2 - fractial2 = -2.2 - 0.8 = -3
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++fractial;
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}
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// Check if the value is already rounded or we force-round down or up
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if (FlexLayoutDoubleEqual(fractial, 0) || forceFloor) {
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scaledValue = scaledValue - fractial;
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} else if (FlexLayoutDoubleEqual(fractial, 1.0f) || forceCeil) {
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scaledValue = scaledValue - fractial + 1.0f;
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} else {
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// Finally we just round the value
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scaledValue = scaledValue - fractial +
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(isDefined(fractial) &&
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(fractial > 0.5f || FlexLayoutDoubleEqual(fractial, 0.5f))
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? 1.0f
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: 0.0f);
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}
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return static_cast<Float>(scaledValue / pointScaleFactor);
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}
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} // namespace algo
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} // namespace flexlayout
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} // namespace facebook
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