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// Copyright (C) 2018 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
#ifndef QCOLORTRANSFERFUNCTION_P_H
#define QCOLORTRANSFERFUNCTION_P_H
//
// W A R N I N G
// -------------
//
// This file is not part of the Qt API. It exists purely as an
// implementation detail. This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//
#include <QtGui/private/qtguiglobal_p.h>
#include <QtCore/QFlags>
#include <cmath>
QT_BEGIN_NAMESPACE
// Defines a ICC parametric curve type 4
class QColorTransferFunction
{
public:
QColorTransferFunction() noexcept
: m_a(1.0f), m_b(0.0f), m_c(1.0f), m_d(0.0f), m_e(0.0f), m_f(0.0f), m_g(1.0f)
, m_flags(Hints(Hint::Calculated) | Hint::IsGamma | Hint::IsIdentity)
{ }
QColorTransferFunction(float a, float b, float c, float d, float e, float f, float g) noexcept
: m_a(a), m_b(b), m_c(c), m_d(d), m_e(e), m_f(f), m_g(g), m_flags()
{ }
bool isGamma() const
{
updateHints();
return m_flags & Hint::IsGamma;
}
bool isIdentity() const
{
updateHints();
return m_flags & Hint::IsIdentity;
}
bool isSRgb() const
{
updateHints();
return m_flags & Hint::IsSRgb;
}
float apply(float x) const
{
if (x < m_d)
return m_c * x + m_f;
float t = std::pow(m_a * x + m_b, m_g);
if (std::isfinite(t))
return t + m_e;
if (t > 0.f)
return 1.f;
else
return 0.f;
}
QColorTransferFunction inverted() const
{
float a, b, c, d, e, f, g;
d = m_c * m_d + m_f;
if (std::isnormal(m_c)) {
c = 1.0f / m_c;
f = -m_f / m_c;
} else {
c = 0.0f;
f = 0.0f;
}
bool valid_abeg = std::isnormal(m_a) && std::isnormal(m_g);
if (valid_abeg)
a = std::pow(1.0f / m_a, m_g);
if (valid_abeg && !std::isfinite(a))
valid_abeg = false;
if (valid_abeg) {
b = -a * m_e;
e = -m_b / m_a;
g = 1.0f / m_g;
} else {
a = 0.0f;
b = 0.0f;
e = 1.0f;
g = 1.0f;
}
return QColorTransferFunction(a, b, c, d, e, f, g);
}
// A few predefined curves:
static QColorTransferFunction fromGamma(float gamma)
{
return QColorTransferFunction(1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, gamma,
Hints(Hint::Calculated) | Hint::IsGamma |
(paramCompare(gamma, 1.0f) ? Hint::IsIdentity : Hint::NoHint));
}
static QColorTransferFunction fromSRgb()
{
return QColorTransferFunction(1.0f / 1.055f, 0.055f / 1.055f, 1.0f / 12.92f, 0.04045f, 0.0f, 0.0f, 2.4f,
Hints(Hint::Calculated) | Hint::IsSRgb);
}
static QColorTransferFunction fromProPhotoRgb()
{
return QColorTransferFunction(1.0f, 0.0f, 1.0f / 16.0f, 16.0f / 512.0f, 0.0f, 0.0f, 1.8f,
Hints(Hint::Calculated));
}
bool matches(const QColorTransferFunction &o) const
{
return paramCompare(m_a, o.m_a) && paramCompare(m_b, o.m_b)
&& paramCompare(m_c, o.m_c) && paramCompare(m_d, o.m_d)
&& paramCompare(m_e, o.m_e) && paramCompare(m_f, o.m_f)
&& paramCompare(m_g, o.m_g);
}
friend inline bool operator==(const QColorTransferFunction &f1, const QColorTransferFunction &f2);
friend inline bool operator!=(const QColorTransferFunction &f1, const QColorTransferFunction &f2);
float m_a;
float m_b;
float m_c;
float m_d;
float m_e;
float m_f;
float m_g;
enum class Hint : quint32 {
NoHint = 0,
Calculated = 1,
IsGamma = 2,
IsIdentity = 4,
IsSRgb = 8
};
Q_DECLARE_FLAGS(Hints, Hint);
private:
QColorTransferFunction(float a, float b, float c, float d, float e, float f, float g, Hints flags) noexcept
: m_a(a), m_b(b), m_c(c), m_d(d), m_e(e), m_f(f), m_g(g), m_flags(flags)
{ }
static inline bool paramCompare(float p1, float p2)
{
// Much fuzzier than fuzzy compare.
// It tries match parameters that has been passed through a 8.8
// fixed point form.
return (qAbs(p1 - p2) <= (1.0f / 512.0f));
}
void updateHints() const
{
if (m_flags & Hint::Calculated)
return;
// We do not consider the case with m_d = 1.0f linear or simple,
// since it wouldn't be linear for applyExtended().
bool simple = paramCompare(m_a, 1.0f) && paramCompare(m_b, 0.0f)
&& paramCompare(m_d, 0.0f)
&& paramCompare(m_e, 0.0f);
if (simple) {
m_flags |= Hint::IsGamma;
if (qFuzzyCompare(m_g, 1.0f))
m_flags |= Hint::IsIdentity;
} else {
if (*this == fromSRgb())
m_flags |= Hint::IsSRgb;
}
m_flags |= Hint::Calculated;
}
mutable Hints m_flags;
};
Q_DECLARE_OPERATORS_FOR_FLAGS(QColorTransferFunction::Hints);
inline bool operator==(const QColorTransferFunction &f1, const QColorTransferFunction &f2)
{
return f1.matches(f2);
}
inline bool operator!=(const QColorTransferFunction &f1, const QColorTransferFunction &f2)
{
return !f1.matches(f2);
}
QT_END_NAMESPACE
#endif // QCOLORTRANSFERFUNCTION_P_H
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