Improve QColorTrc::isLinear and rename it isIdentity

Pick-to: 6.7
Change-Id: Id697fa3844610606c202e3fa717d631a3621e774
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

5 files changed, 53 insertions, 24 deletions

diff --git a/src/gui/painting/qcolorspace.cpp b/src/gui/painting/qcolorspace.cpp
index 487c295298..539a294102 100644
--- a/src/gui/painting/qcolorspace.cpp
+++ b/src/gui/painting/qcolorspace.cpp
@@ -319,7 +319,7 @@ void QColorSpacePrivate::setTransferFunctionTable(const QList<uint16_t> &transfe
     QColorTransferFunction curve;
     if (table.asColorTransferFunction(&curve)) {
         // Table recognized as a specific curve
-        if (curve.isLinear()) {
+        if (curve.isIdentity()) {
             transferFunction = QColorSpace::TransferFunction::Linear;
             gamma = 1.0f;
         } else if (curve.isSRgb()) {
diff --git a/src/gui/painting/qcolortransferfunction_p.h b/src/gui/painting/qcolortransferfunction_p.h
index a9bb26df59..8bbce3ca99 100644
--- a/src/gui/painting/qcolortransferfunction_p.h
+++ b/src/gui/painting/qcolortransferfunction_p.h
@@ -26,7 +26,8 @@ class Q_GUI_EXPORT 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(0)
+            : 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(quint32(Hints::Calculated) | quint32(Hints::IsGamma) | quint32(Hints::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(0)
@@ -37,10 +38,10 @@ public:
         updateHints();
         return m_flags & quint32(Hints::IsGamma);
     }
-    bool isLinear() const
+    bool isIdentity() const
     {
         updateHints();
-        return m_flags & quint32(Hints::IsLinear);
+        return m_flags & quint32(Hints::IsIdentity);
     }
     bool isSRgb() const
     {
@@ -88,15 +89,19 @@ public:
     // A few predefined curves:
     static QColorTransferFunction fromGamma(float gamma)
     {
-        return QColorTransferFunction(1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, gamma);
+        return QColorTransferFunction(1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, gamma,
+                                      quint32(Hints::Calculated) | quint32(Hints::IsGamma) |
+                                      (paramCompare(gamma, 1.0f) ? quint32(Hints::IsIdentity) : 0));
     }
     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);
+        return QColorTransferFunction(1.0f / 1.055f, 0.055f / 1.055f, 1.0f / 12.92f, 0.04045f, 0.0f, 0.0f, 2.4f,
+                                      quint32(Hints::Calculated) | quint32(Hints::IsSRgb));
     }
     static QColorTransferFunction fromProPhotoRgb()
     {
-        return QColorTransferFunction(1.0f, 0.0f, 1.0f / 16.0f, 16.0f / 512.0f, 0.0f, 0.0f, 1.8f);
+        return QColorTransferFunction(1.0f, 0.0f, 1.0f / 16.0f, 16.0f / 512.0f, 0.0f, 0.0f, 1.8f,
+                                      quint32(Hints::Calculated));
     }
     bool matches(const QColorTransferFunction &o) const
     {
@@ -117,6 +122,9 @@ public:
     float m_g;
 
 private:
+    QColorTransferFunction(float a, float b, float c, float d, float e, float f, float g, quint32 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.
@@ -137,7 +145,7 @@ private:
         if (simple) {
             m_flags |= quint32(Hints::IsGamma);
             if (qFuzzyCompare(m_g, 1.0f))
-                m_flags |= quint32(Hints::IsLinear);
+                m_flags |= quint32(Hints::IsIdentity);
         } else {
             if (*this == fromSRgb())
                 m_flags |= quint32(Hints::IsSRgb);
@@ -147,7 +155,7 @@ private:
     enum class Hints : quint32 {
         Calculated = 1,
         IsGamma = 2,
-        IsLinear = 4,
+        IsIdentity = 4,
         IsSRgb = 8
     };
     mutable quint32 m_flags;
diff --git a/src/gui/painting/qcolortransfertable_p.h b/src/gui/painting/qcolortransfertable_p.h
index dc0f5804fd..20c35cac2d 100644
--- a/src/gui/painting/qcolortransfertable_p.h
+++ b/src/gui/painting/qcolortransfertable_p.h
@@ -48,6 +48,17 @@ public:
         return m_tableSize == 0;
     }
 
+    bool isIdentity() const
+    {
+        if (isEmpty())
+            return true;
+        if (m_tableSize != 2)
+            return false;
+        if (!m_table8.isEmpty())
+            return m_table8[0] == 0 && m_table8[1] == 255;
+        return m_table16[0] == 0 && m_table16[1] == 65535;
+    }
+
     bool checkValidity() const
     {
         if (isEmpty())
@@ -137,6 +148,10 @@ public:
     bool asColorTransferFunction(QColorTransferFunction *transferFn)
     {
         Q_ASSERT(transferFn);
+        if (isEmpty()) {
+            *transferFn = QColorTransferFunction();
+            return true;
+        }
         if (m_tableSize < 2)
             return false;
         if (!m_table8.isEmpty() && (m_table8[0] != 0 || m_table8[m_tableSize - 1] != 255))
diff --git a/src/gui/painting/qcolortrc_p.h b/src/gui/painting/qcolortrc_p.h
index 9e879bb3e2..6f9030fa3a 100644
--- a/src/gui/painting/qcolortrc_p.h
+++ b/src/gui/painting/qcolortrc_p.h
@@ -39,9 +39,11 @@ public:
         Table
     };
 
-    bool isLinear() const
+    bool isIdentity() const
     {
-        return m_type == Type::Uninitialized || (m_type == Type::Function && m_fun.isLinear());
+        return m_type == Type::Uninitialized
+           || (m_type == Type::Function && m_fun.isIdentity())
+           || (m_type == Type::Table && m_table.isIdentity());
     }
     bool isValid() const
     {
diff --git a/src/gui/painting/qicc.cpp b/src/gui/painting/qicc.cpp
index f36c1db62b..d0bfa7eaa3 100644
--- a/src/gui/painting/qicc.cpp
+++ b/src/gui/painting/qicc.cpp
@@ -238,7 +238,7 @@ static bool isValidIccProfile(const ICCProfileHeader &header)
 
 static int writeColorTrc(QDataStream &stream, const QColorTrc &trc)
 {
-    if (trc.isLinear()) {
+    if (trc.isIdentity()) {
         stream << uint(Tag::curv) << uint(0);
         stream << uint(0);
         return 12;
@@ -698,26 +698,30 @@ static bool parseTRCs(const QByteArray &data, const QHash<Tag, TagEntry> &tagInd
         qCWarning(lcIcc) << "fromIccProfile: Invalid bTRC";
         return false;
     }
-    if (rCurve == gCurve && gCurve == bCurve && rCurve.m_type == QColorTrc::Type::Function) {
-        if (rCurve.m_fun.isLinear()) {
+    if (rCurve == gCurve && gCurve == bCurve)  {
+        if (rCurve.isIdentity()) {
             qCDebug(lcIcc) << "fromIccProfile: Linear gamma detected";
             colorspaceDPtr->trc[0] = QColorTransferFunction();
             colorspaceDPtr->transferFunction = QColorSpace::TransferFunction::Linear;
             colorspaceDPtr->gamma = 1.0f;
-        } else if (rCurve.m_fun.isGamma()) {
-            qCDebug(lcIcc) << "fromIccProfile: Simple gamma detected";
-            colorspaceDPtr->trc[0] = QColorTransferFunction::fromGamma(rCurve.m_fun.m_g);
-            colorspaceDPtr->transferFunction = QColorSpace::TransferFunction::Gamma;
-            colorspaceDPtr->gamma = rCurve.m_fun.m_g;
-        } else if (rCurve.m_fun.isSRgb()) {
-            qCDebug(lcIcc) << "fromIccProfile: sRGB gamma detected";
-            colorspaceDPtr->trc[0] = QColorTransferFunction::fromSRgb();
-            colorspaceDPtr->transferFunction = QColorSpace::TransferFunction::SRgb;
+        } else if (rCurve.m_type == QColorTrc::Type::Function) {
+            if (rCurve.m_fun.isGamma()) {
+                qCDebug(lcIcc) << "fromIccProfile: Simple gamma detected";
+                colorspaceDPtr->trc[0] = QColorTransferFunction::fromGamma(rCurve.m_fun.m_g);
+                colorspaceDPtr->transferFunction = QColorSpace::TransferFunction::Gamma;
+                colorspaceDPtr->gamma = rCurve.m_fun.m_g;
+            } else if (rCurve.m_fun.isSRgb()) {
+                qCDebug(lcIcc) << "fromIccProfile: sRGB gamma detected";
+                colorspaceDPtr->trc[0] = QColorTransferFunction::fromSRgb();
+                colorspaceDPtr->transferFunction = QColorSpace::TransferFunction::SRgb;
+            } else {
+                colorspaceDPtr->trc[0] = rCurve;
+                colorspaceDPtr->transferFunction = QColorSpace::TransferFunction::Custom;
+            }
         } else {
             colorspaceDPtr->trc[0] = rCurve;
             colorspaceDPtr->transferFunction = QColorSpace::TransferFunction::Custom;
         }
-
         colorspaceDPtr->trc[1] = colorspaceDPtr->trc[0];
         colorspaceDPtr->trc[2] = colorspaceDPtr->trc[0];
     } else {