qcolortransferfunction_p.h

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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