1// Copyright (C) 2018 The Qt Company Ltd.
2// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
3
4#ifndef QCOLORTRANSFERFUNCTION_P_H
5#define QCOLORTRANSFERFUNCTION_P_H
6
7//
8// W A R N I N G
9// -------------
10//
11// This file is not part of the Qt API. It exists purely as an
12// implementation detail. This header file may change from version to
13// version without notice, or even be removed.
14//
15// We mean it.
16//
17
18#include <QtGui/private/qtguiglobal_p.h>
19#include <QtCore/QFlags>
20
21#include <cmath>
22
23QT_BEGIN_NAMESPACE
24
25// Defines a ICC parametric curve type 4
26class QColorTransferFunction
27{
28public:
29 QColorTransferFunction() noexcept
30 : 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)
31 , m_flags(Hints(Hint::Calculated) | Hint::IsGamma | Hint::IsIdentity)
32 { }
33
34 QColorTransferFunction(float a, float b, float c, float d, float e, float f, float g) noexcept
35 : m_a(a), m_b(b), m_c(c), m_d(d), m_e(e), m_f(f), m_g(g), m_flags()
36 { }
37
38 bool isGamma() const
39 {
40 updateHints();
41 return m_flags & Hint::IsGamma;
42 }
43 bool isIdentity() const
44 {
45 updateHints();
46 return m_flags & Hint::IsIdentity;
47 }
48 bool isSRgb() const
49 {
50 updateHints();
51 return m_flags & Hint::IsSRgb;
52 }
53
54 float apply(float x) const
55 {
56 if (x < m_d)
57 return m_c * x + m_f;
58 float t = std::pow(x: m_a * x + m_b, y: m_g);
59 if (std::isfinite(x: t))
60 return t + m_e;
61 if (t > 0.f)
62 return 1.f;
63 else
64 return 0.f;
65 }
66
67 QColorTransferFunction inverted() const
68 {
69 float a, b, c, d, e, f, g;
70
71 d = m_c * m_d + m_f;
72
73 if (std::isnormal(x: m_c)) {
74 c = 1.0f / m_c;
75 f = -m_f / m_c;
76 } else {
77 c = 0.0f;
78 f = 0.0f;
79 }
80
81 bool valid_abeg = std::isnormal(x: m_a) && std::isnormal(x: m_g);
82 if (valid_abeg)
83 a = std::pow(x: 1.0f / m_a, y: m_g);
84 if (valid_abeg && !std::isfinite(x: a))
85 valid_abeg = false;
86 if (valid_abeg) {
87 b = -a * m_e;
88 e = -m_b / m_a;
89 g = 1.0f / m_g;
90 } else {
91 a = 0.0f;
92 b = 0.0f;
93 e = 1.0f;
94 g = 1.0f;
95 }
96
97 return QColorTransferFunction(a, b, c, d, e, f, g);
98 }
99
100 // A few predefined curves:
101 static QColorTransferFunction fromGamma(float gamma)
102 {
103 return QColorTransferFunction(1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, gamma,
104 Hints(Hint::Calculated) | Hint::IsGamma |
105 (paramCompare(p1: gamma, p2: 1.0f) ? Hint::IsIdentity : Hint::NoHint));
106 }
107 static QColorTransferFunction fromSRgb()
108 {
109 return QColorTransferFunction(1.0f / 1.055f, 0.055f / 1.055f, 1.0f / 12.92f, 0.04045f, 0.0f, 0.0f, 2.4f,
110 Hints(Hint::Calculated) | Hint::IsSRgb);
111 }
112 static QColorTransferFunction fromProPhotoRgb()
113 {
114 return QColorTransferFunction(1.0f, 0.0f, 1.0f / 16.0f, 16.0f / 512.0f, 0.0f, 0.0f, 1.8f,
115 Hints(Hint::Calculated));
116 }
117 static QColorTransferFunction fromBt2020()
118 {
119 return QColorTransferFunction(1.0f / 1.0993f, 0.0993f / 1.0993f, 1.0f / 4.5f, 0.08145f, 0.0f, 0.0f, 2.2f,
120 Hints(Hint::Calculated));
121 }
122 bool matches(const QColorTransferFunction &o) const
123 {
124 return paramCompare(p1: m_a, p2: o.m_a) && paramCompare(p1: m_b, p2: o.m_b)
125 && paramCompare(p1: m_c, p2: o.m_c) && paramCompare(p1: m_d, p2: o.m_d)
126 && paramCompare(p1: m_e, p2: o.m_e) && paramCompare(p1: m_f, p2: o.m_f)
127 && paramCompare(p1: m_g, p2: o.m_g);
128 }
129 friend inline bool operator==(const QColorTransferFunction &f1, const QColorTransferFunction &f2);
130 friend inline bool operator!=(const QColorTransferFunction &f1, const QColorTransferFunction &f2);
131
132 float m_a;
133 float m_b;
134 float m_c;
135 float m_d;
136 float m_e;
137 float m_f;
138 float m_g;
139
140 enum class Hint : quint32 {
141 NoHint = 0,
142 Calculated = 1,
143 IsGamma = 2,
144 IsIdentity = 4,
145 IsSRgb = 8
146 };
147
148 Q_DECLARE_FLAGS(Hints, Hint);
149
150private:
151 QColorTransferFunction(float a, float b, float c, float d, float e, float f, float g, Hints flags) noexcept
152 : m_a(a), m_b(b), m_c(c), m_d(d), m_e(e), m_f(f), m_g(g), m_flags(flags)
153 { }
154 static inline bool paramCompare(float p1, float p2)
155 {
156 // Much fuzzier than fuzzy compare.
157 // It tries match parameters that has been passed through a 8.8
158 // fixed point form.
159 return (qAbs(t: p1 - p2) <= (1.0f / 512.0f));
160 }
161
162 void updateHints() const
163 {
164 if (m_flags & Hint::Calculated)
165 return;
166 // We do not consider the case with m_d = 1.0f linear or simple,
167 // since it wouldn't be linear for applyExtended().
168 bool simple = paramCompare(p1: m_a, p2: 1.0f) && paramCompare(p1: m_b, p2: 0.0f)
169 && paramCompare(p1: m_d, p2: 0.0f)
170 && paramCompare(p1: m_e, p2: 0.0f);
171 if (simple) {
172 m_flags |= Hint::IsGamma;
173 if (qFuzzyCompare(p1: m_g, p2: 1.0f))
174 m_flags |= Hint::IsIdentity;
175 } else {
176 if (*this == fromSRgb())
177 m_flags |= Hint::IsSRgb;
178 }
179 m_flags |= Hint::Calculated;
180 }
181
182 mutable Hints m_flags;
183};
184
185Q_DECLARE_OPERATORS_FOR_FLAGS(QColorTransferFunction::Hints);
186
187inline bool operator==(const QColorTransferFunction &f1, const QColorTransferFunction &f2)
188{
189 return f1.matches(o: f2);
190}
191inline bool operator!=(const QColorTransferFunction &f1, const QColorTransferFunction &f2)
192{
193 return !f1.matches(o: f2);
194}
195
196QT_END_NAMESPACE
197
198#endif // QCOLORTRANSFERFUNCTION_P_H
199

source code of qtbase/src/gui/painting/qcolortransferfunction_p.h