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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#ifndef mozilla_AspectRatio_h
#define mozilla_AspectRatio_h
/* The aspect ratio of a box, in a "width / height" format. */
#include "mozilla/Attributes.h"
#include "mozilla/gfx/BaseSize.h"
#include "nsCoord.h"
#include <algorithm>
#include <limits>
namespace IPC {
template <typename T>
struct ParamTraits;
} // namespace IPC
namespace mozilla {
enum class LogicalAxis : uint8_t;
class LogicalSize;
class WritingMode;
enum class UseBoxSizing : uint8_t {
// The aspect ratio works with content box dimensions always.
// The aspect ratio works with the dimensions of the box specified by
// box-sizing.
struct AspectRatio {
friend struct IPC::ParamTraits<mozilla::AspectRatio>;
AspectRatio() = default;
explicit AspectRatio(float aRatio,
UseBoxSizing aUseBoxSizing = UseBoxSizing::No)
: mRatio(std::max(aRatio, 0.0f)), mUseBoxSizing(aUseBoxSizing) {}
static AspectRatio FromSize(float aWidth, float aHeight,
UseBoxSizing aUseBoxSizing = UseBoxSizing::No) {
if (aWidth == 0.0f || aHeight == 0.0f) {
// For the degenerate ratio, we don't care about which box sizing we are
// using, so using default constructor is fine.
return AspectRatio();
return AspectRatio(aWidth / aHeight, aUseBoxSizing);
template <typename T, typename Sub, typename Coord>
static AspectRatio FromSize(const gfx::BaseSize<T, Sub, Coord>& aSize) {
return FromSize(aSize.Width(), aSize.Height());
explicit operator bool() const { return mRatio != 0.0f; }
nscoord ApplyTo(nscoord aCoord) const {
return NSCoordSaturatingNonnegativeMultiply(aCoord, mRatio);
float ApplyToFloat(float aFloat) const {
return mRatio * aFloat;
// Inverts the ratio, in order to get the height / width ratio.
[[nodiscard]] AspectRatio Inverted() const {
if (!*this) {
return AspectRatio();
// Clamp to a small epsilon, in case mRatio is absurdly large & produces
// 0.0f in the division here (so that valid ratios always generate other
// valid ratios when inverted).
return AspectRatio(
std::max(std::numeric_limits<float>::epsilon(), 1.0f / mRatio),
[[nodiscard]] inline AspectRatio ConvertToWritingMode(
const WritingMode& aWM) const;
* This method computes the ratio-dependent size by the ratio-determining size
* and aspect-ratio (i.e. preferred aspect ratio). Basically this function
* will be used in the calculation of 'auto' sizes when the preferred
* aspect ratio is not 'auto'.
* @param aRatioDependentAxis The ratio depenedent axis of the box.
* @param aWM The writing mode of the box.
* @param aRatioDetermingSize The content-box size on the ratio determining
* axis. Basically, we use this size and |mRatio|
* to compute the size on the ratio-dependent
* axis.
* @param aContentBoxSizeToBoxSizingAdjust The border padding box size
* adjustment. We need this because
* aspect-ratio should take the
* box-sizing into account if its
* style is '<ratio>'. If its style
* is 'auto & <ratio>', we should use
* content-box dimensions always.
* If the callers want the ratio to
* apply to the content-box size, we
* should pass a zero LogicalSize.
* If mUseBoxSizing is No, we ignore
* this parameter because we should
* use content box dimensions always.
* The return value is the content-box size on the ratio-dependent axis.
* Plese see the definition of the ratio-dependent axis and the
* ratio-determining axis in the spec:
[[nodiscard]] nscoord ComputeRatioDependentSize(
LogicalAxis aRatioDependentAxis, const WritingMode& aWM,
nscoord aRatioDeterminingSize,
const LogicalSize& aContentBoxSizeToBoxSizingAdjust) const;
bool operator==(const AspectRatio& aOther) const {
return mRatio == aOther.mRatio && mUseBoxSizing == aOther.mUseBoxSizing;
bool operator!=(const AspectRatio& aOther) const {
return !(*this == aOther);
bool operator<(const AspectRatio& aOther) const {
mUseBoxSizing == aOther.mUseBoxSizing,
"Do not compare AspectRatio if their mUseBoxSizing are different.");
return mRatio < aOther.mRatio;
// 0.0f represents no aspect ratio.
float mRatio = 0.0f;
UseBoxSizing mUseBoxSizing = UseBoxSizing::No;
} // namespace mozilla
#endif // mozilla_AspectRatio_h