Simplify QColorSpacePrivate initialization

QColorVector and QColorMatrix are default-constructed following the
Qt philosophy of types always being well-defined. The corner-case where
we need uninitialized versions of these types for performance reasons
is handled explicitly.

Change-Id: I629334d1ffc63563ec9fd1298c623946e0799d1d
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/gui/painting/qcolormatrix_p.h

@@ -62,17 +62,16 @@ class QColorVector
 {
 public:
     QColorVector() = default;
-    Q_DECL_CONSTEXPR QColorVector(float x, float y, float z) : x(x), y(y), z(z), _unused(0.0f) { }
+    Q_DECL_CONSTEXPR QColorVector(float x, float y, float z) : x(x), y(y), z(z) { }
     explicit Q_DECL_CONSTEXPR QColorVector(const QPointF &chr) // from XY chromaticity
             : x(chr.x() / chr.y())
             , y(1.0f)
             , z((1.0 - chr.x() - chr.y()) / chr.y())
-            , _unused(0.0f)
     { }
-    float x; // X, x or red
-    float y; // Y, y or green
-    float z; // Z, Y or blue
-    float _unused;
+    float x = 0.0f; // X, x or red
+    float y = 0.0f; // Y, y or green
+    float z = 0.0f; // Z, Y or blue
+    float _unused = 0.0f;
 
     friend inline bool operator==(const QColorVector &v1, const QColorVector &v2);
     friend inline bool operator!=(const QColorVector &v1, const QColorVector &v2);
@@ -81,7 +80,6 @@ public:
         return !x && !y && !z;
     }
 
-    static Q_DECL_CONSTEXPR QColorVector null() { return QColorVector(0.0f, 0.0f, 0.0f); }
     static bool isValidChromaticity(const QPointF &chr)
     {
         if (chr.x() < qreal(0.0) || chr.x() > qreal(1.0))
@@ -187,10 +185,6 @@ public:
                               { r.z, g.z, b.z } };
     }
 
-    static QColorMatrix null()
-    {
-        return { QColorVector::null(), QColorVector::null(), QColorVector::null() };
-    }
     static QColorMatrix identity()
     {
         return { { 1.0f, 0.0f, 0.0f }, { 0.0f, 1.0f, 0.0f }, { 0.0f, 0.0f, 1.0f } };

src/gui/painting/qcolorspace.cpp

@@ -146,17 +146,11 @@ QColorMatrix QColorSpacePrimaries::toXyzMatrix() const
 }
 
 QColorSpacePrivate::QColorSpacePrivate()
-        : primaries(QColorSpace::Primaries::Custom)
-        , transferFunction(QColorSpace::TransferFunction::Custom)
-        , gamma(0.0f)
-        , whitePoint(QColorVector::null())
-        , toXyz(QColorMatrix::null())
 {
 }
 
 QColorSpacePrivate::QColorSpacePrivate(QColorSpace::NamedColorSpace namedColorSpace)
         : namedColorSpace(namedColorSpace)
-        , gamma(0.0f)
 {
     switch (namedColorSpace) {
     case QColorSpace::SRgb:
@@ -282,7 +276,7 @@ void QColorSpacePrivate::initialize()
 void QColorSpacePrivate::setToXyzMatrix()
 {
     if (primaries == QColorSpace::Primaries::Custom) {
-        toXyz = QColorMatrix::null();
+        toXyz = QColorMatrix();
         whitePoint = QColorVector::D50();
         return;
     }

src/gui/painting/qcolorspace_p.h

@@ -124,9 +124,9 @@ public:
     static constexpr QColorSpace::NamedColorSpace Unknown = QColorSpace::NamedColorSpace(0);
     QColorSpace::NamedColorSpace namedColorSpace = Unknown;
 
-    QColorSpace::Primaries primaries;
-    QColorSpace::TransferFunction transferFunction;
-    float gamma;
+    QColorSpace::Primaries primaries = QColorSpace::Primaries::Custom;
+    QColorSpace::TransferFunction transferFunction = QColorSpace::TransferFunction::Custom;
+    float gamma = 0.0f;
     QColorVector whitePoint;
 
     QColorTrc trc[3];

src/gui/painting/qcolortransform.cpp

@@ -612,6 +612,15 @@ static void storeOpaque(QRgba64 *dst, const QRgba64 *src, const QColorVector *bu
 
 static constexpr qsizetype WorkBlockSize = 256;
 
+template <typename T, int Count = 1>
+class QUninitialized
+{
+public:
+    operator T*() { return reinterpret_cast<T *>(this); }
+private:
+    alignas(T) char data[sizeof(T) * Count];
+};
+
 template<typename T>
 void QColorTransformPrivate::apply(T *dst, const T *src, qsizetype count, TransformFlags flags) const
 {
@@ -623,7 +632,8 @@ void QColorTransformPrivate::apply(T *dst, const T *src, qsizetype count, Transf
 
     bool doApplyMatrix = (colorMatrix != QColorMatrix::identity());
 
-    QColorVector buffer[WorkBlockSize];
+    QUninitialized<QColorVector, WorkBlockSize> buffer;
+
     qsizetype i = 0;
     while (i < count) {
         const qsizetype len = qMin(count - i, WorkBlockSize);