Expand QColorTransform

Add comparison operators and an isIdentity() method to detect (1-1)
transforms.

[ChangeLog][QtGui] Added QColorTransform::isIdentity() method. Added QImage::colorTransformed() transitive method.

Change-Id: I5fbcd14e75f2179e43e94e8c5f42cd0a5600790b
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

8 files changed, 135 insertions, 13 deletions

diff --git a/src/gui/image/qimage.cpp b/src/gui/image/qimage.cpp
index 5027a09a09..57900d4379 100644
--- a/src/gui/image/qimage.cpp
+++ b/src/gui/image/qimage.cpp
@@ -1,4 +1,4 @@
-// Copyright (C) 2021 The Qt Company Ltd.
+// Copyright (C) 2022 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
 
 #include "qimage.h"
@@ -4979,6 +4979,8 @@ QImage QImage::convertedToColorSpace(const QColorSpace &colorSpace) const
 {
     if (!d || !d->colorSpace.isValid() || !colorSpace.isValid())
         return QImage();
+    if (d->colorSpace == colorSpace)
+        return *this;
     QImage image = copy();
     image.convertToColorSpace(colorSpace);
     return image;
@@ -5003,6 +5005,8 @@ QColorSpace QImage::colorSpace() const
 */
 void QImage::applyColorTransform(const QColorTransform &transform)
 {
+    if (transform.isIdentity())
+        return;
     detach();
     if (!d)
         return;
@@ -5054,21 +5058,21 @@ void QImage::applyColorTransform(const QColorTransform &transform)
         transformSegment = [&](int yStart, int yEnd) {
             for (int y = yStart; y < yEnd; ++y) {
                 QRgbaFloat32 *scanline = reinterpret_cast<QRgbaFloat32 *>(d->data + y * d->bytes_per_line);
-                transform.d->apply(scanline, scanline, width(), flags);
+                QColorTransformPrivate::get(transform)->apply(scanline, scanline, width(), flags);
             }
         };
     } else  if (depth() > 32) {
         transformSegment = [&](int yStart, int yEnd) {
             for (int y = yStart; y < yEnd; ++y) {
                 QRgba64 *scanline = reinterpret_cast<QRgba64 *>(d->data + y * d->bytes_per_line);
-                transform.d->apply(scanline, scanline, width(), flags);
+                QColorTransformPrivate::get(transform)->apply(scanline, scanline, width(), flags);
             }
         };
     } else {
         transformSegment = [&](int yStart, int yEnd) {
             for (int y = yStart; y < yEnd; ++y) {
                 QRgb *scanline = reinterpret_cast<QRgb *>(d->data + y * d->bytes_per_line);
-                transform.d->apply(scanline, scanline, width(), flags);
+                QColorTransformPrivate::get(transform)->apply(scanline, scanline, width(), flags);
             }
         };
     }
@@ -5097,6 +5101,39 @@ void QImage::applyColorTransform(const QColorTransform &transform)
         *this = std::move(*this).convertToFormat(oldFormat);
 }
 
+/*!
+    \since 6.4
+
+    Returns the image color transformed using \a transform on all pixels in the image.
+
+    \sa applyColorTransform()
+*/
+QImage QImage::colorTransformed(const QColorTransform &transform) const &
+{
+    if (!d || !d->colorSpace.isValid())
+        return QImage();
+    if (transform.isIdentity())
+        return *this;
+    QImage image = copy();
+    image.applyColorTransform(transform);
+    return image;
+}
+
+/*!
+    \since 6.4
+    \overload
+
+    Returns the image color transformed using \a transform on all pixels in the image.
+
+    \sa applyColorTransform()
+*/
+QImage QImage::colorTransformed(const QColorTransform &transform) &&
+{
+    if (!d || !d->colorSpace.isValid())
+        return QImage();
+    applyColorTransform(transform);
+    return std::move(*this);
+}
 
 bool QImageData::convertInPlace(QImage::Format newFormat, Qt::ImageConversionFlags flags)
 {
diff --git a/src/gui/image/qimage.h b/src/gui/image/qimage.h
index fd42813115..9e4abd006e 100644
--- a/src/gui/image/qimage.h
+++ b/src/gui/image/qimage.h
@@ -234,6 +234,8 @@ public:
     void convertToColorSpace(const QColorSpace &);
     void setColorSpace(const QColorSpace &);
 
+    QImage colorTransformed(const QColorTransform &transform) const &;
+    QImage colorTransformed(const QColorTransform &transform) &&;
     void applyColorTransform(const QColorTransform &transform);
 
     bool load(QIODevice *device, const char *format);
diff --git a/src/gui/image/qimage_conversions.cpp b/src/gui/image/qimage_conversions.cpp
index 433134ff7e..fa75bed3c8 100644
--- a/src/gui/image/qimage_conversions.cpp
+++ b/src/gui/image/qimage_conversions.cpp
@@ -1418,7 +1418,7 @@ static void convert_ARGB_to_gray8(QImageData *dest, const QImageData *src, Qt::I
 
     QColorSpace fromCS = src->colorSpace.isValid() ? src->colorSpace : QColorSpace::SRgb;
     QColorTransform tf = QColorSpacePrivate::get(fromCS)->transformationToXYZ();
-    QColorTransformPrivate *tfd = QColorTransformPrivate::get(tf);
+    const QColorTransformPrivate *tfd = QColorTransformPrivate::get(tf);
     QColorTransformPrivate::TransformFlags flags = Premultiplied
             ? QColorTransformPrivate::InputPremultiplied
             : QColorTransformPrivate::Unpremultiplied;
@@ -1448,7 +1448,7 @@ static void convert_ARGB_to_gray16(QImageData *dest, const QImageData *src, Qt::
 
     QColorSpace fromCS = src->colorSpace.isValid() ? src->colorSpace : QColorSpace::SRgb;
     QColorTransform tf = QColorSpacePrivate::get(fromCS)->transformationToXYZ();
-    QColorTransformPrivate *tfd = QColorTransformPrivate::get(tf);
+    const QColorTransformPrivate *tfd = QColorTransformPrivate::get(tf);
     QColorTransformPrivate::TransformFlags flags = Premultiplied
             ? QColorTransformPrivate::InputPremultiplied
             : QColorTransformPrivate::Unpremultiplied;
@@ -1487,7 +1487,7 @@ static void convert_RGBA64_to_gray8(QImageData *dest, const QImageData *src, Qt:
 
     QColorSpace fromCS = src->colorSpace.isValid() ? src->colorSpace : QColorSpace::SRgb;
     QColorTransform tf = QColorSpacePrivate::get(fromCS)->transformationToXYZ();
-    QColorTransformPrivate *tfd = QColorTransformPrivate::get(tf);
+    const QColorTransformPrivate *tfd = QColorTransformPrivate::get(tf);
     QColorTransformPrivate::TransformFlags flags = Premultiplied
             ? QColorTransformPrivate::InputPremultiplied
             : QColorTransformPrivate::Unpremultiplied;
@@ -1526,7 +1526,7 @@ static void convert_RGBA64_to_gray16(QImageData *dest, const QImageData *src, Qt
 
     QColorSpace fromCS = src->colorSpace.isValid() ? src->colorSpace : QColorSpace::SRgb;
     QColorTransform tf = QColorSpacePrivate::get(fromCS)->transformationToXYZ();
-    QColorTransformPrivate *tfd = QColorTransformPrivate::get(tf);
+    const QColorTransformPrivate *tfd = QColorTransformPrivate::get(tf);
     QColorTransformPrivate::TransformFlags flags = Premultiplied
             ? QColorTransformPrivate::InputPremultiplied
             : QColorTransformPrivate::Unpremultiplied;
diff --git a/src/gui/painting/qcolormatrix_p.h b/src/gui/painting/qcolormatrix_p.h
index cda0d8229a..1ce5df6264 100644
--- a/src/gui/painting/qcolormatrix_p.h
+++ b/src/gui/painting/qcolormatrix_p.h
@@ -101,6 +101,10 @@ public:
                     r.z * (b.y * g.x - g.y * b.x);
         return !qFuzzyIsNull(det);
     }
+    bool isIdentity() const noexcept
+    {
+        return *this == identity();
+    }
 
     QColorMatrix inverted() const
     {
diff --git a/src/gui/painting/qcolorspace.cpp b/src/gui/painting/qcolorspace.cpp
index e8ced30727..7fdfe34872 100644
--- a/src/gui/painting/qcolorspace.cpp
+++ b/src/gui/painting/qcolorspace.cpp
@@ -419,6 +419,8 @@ QColorTransform QColorSpacePrivate::transformationToColorSpace(const QColorSpace
     ptr->colorSpaceIn = this;
     ptr->colorSpaceOut = out;
     ptr->colorMatrix = out->toXyz.inverted() * toXyz;
+    if (ptr->isIdentity())
+        return QColorTransform();
     return combined;
 }
 
@@ -981,6 +983,9 @@ QColorTransform QColorSpace::transformationToColorSpace(const QColorSpace &color
     if (!isValid() || !colorspace.isValid())
         return QColorTransform();
 
+    if (*this == colorspace)
+        return QColorTransform();
+
     return d_ptr->transformationToColorSpace(colorspace.d_ptr.get());
 }
 
diff --git a/src/gui/painting/qcolortransform.cpp b/src/gui/painting/qcolortransform.cpp
index 71b07f30a5..c89909cff4 100644
--- a/src/gui/painting/qcolortransform.cpp
+++ b/src/gui/painting/qcolortransform.cpp
@@ -1,7 +1,6 @@
-// Copyright (C) 2018 The Qt Company Ltd.
+// Copyright (C) 2022 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
 
-
 #include "qcolortransform.h"
 #include "qcolortransform_p.h"
 
@@ -13,6 +12,7 @@
 #include <QtCore/qatomic.h>
 #include <QtCore/qmath.h>
 #include <QtGui/qcolor.h>
+#include <QtGui/qimage.h>
 #include <QtGui/qtransform.h>
 #include <QtCore/private/qsimd_p.h>
 
@@ -105,6 +105,50 @@ QColorTransform::~QColorTransform() = default;
 QT_DEFINE_QESDP_SPECIALIZATION_DTOR(QColorTransformPrivate)
 
 /*!
+    \since 6.4
+    Returns true if the color transform is the identity transform.
+*/
+bool QColorTransform::isIdentity() const noexcept
+{
+    return !d || d->isIdentity();
+}
+
+/*!
+    \fn bool QColorTransform::operator==(const QColorTransform &ct1, const QColorTransform &ct2)
+    \since 6.4
+    Returns true if \a ct1 defines the same color transformation as \a ct2.
+*/
+
+/*!
+    \fn bool QColorTransform::operator!=(const QColorTransform &ct1, const QColorTransform &ct2)
+    \since 6.4
+    Returns true if \a ct1 does not define the same transformation as \a ct2.
+*/
+
+/*! \internal
+*/
+bool QColorTransform::compare(const QColorTransform &other) const
+{
+    if (d == other.d)
+        return true;
+    if (bool(d) != bool(other.d))
+        return d ? d->isIdentity() : other.d->isIdentity();
+    if (d->colorMatrix != other.d->colorMatrix)
+        return false;
+    if (bool(d->colorSpaceIn) != bool(other.d->colorSpaceIn))
+        return false;
+    if (bool(d->colorSpaceOut) != bool(other.d->colorSpaceOut))
+        return false;
+    for (int i = 0; i < 3; ++i) {
+        if (d->colorSpaceIn && d->colorSpaceIn->trc[i] != other.d->colorSpaceIn->trc[i])
+            return false;
+        if (d->colorSpaceOut && d->colorSpaceOut->trc[i] != other.d->colorSpaceOut->trc[i])
+            return false;
+    }
+    return true;
+}
+
+/*!
     Applies the color transformation on the QRgb value \a argb.
 
     The input should be opaque or unpremultiplied.
@@ -1129,7 +1173,7 @@ void QColorTransformPrivate::apply(T *dst, const T *src, qsizetype count, Transf
     updateLutsIn();
     updateLutsOut();
 
-    bool doApplyMatrix = (colorMatrix != QColorMatrix::identity());
+    bool doApplyMatrix = !colorMatrix.isIdentity();
     constexpr bool DoClip = !std::is_same_v<T, QRgbaFloat16> && !std::is_same_v<T, QRgbaFloat32>;
 
     QUninitialized<QColorVector, WorkBlockSize> buffer;
@@ -1281,4 +1325,28 @@ void QColorTransformPrivate::apply(quint16 *dst, const QRgba64 *src, qsizetype c
 }
 
 
+/*!
+    \internal
+*/
+bool QColorTransformPrivate::isIdentity() const
+{
+    if (!colorMatrix.isIdentity())
+        return false;
+    if (colorSpaceIn && colorSpaceOut) {
+        if (colorSpaceIn->transferFunction != colorSpaceOut->transferFunction)
+            return false;
+        if (colorSpaceIn->transferFunction == QColorSpace::TransferFunction::Custom) {
+            return colorSpaceIn->trc[0] == colorSpaceOut->trc[0]
+                && colorSpaceIn->trc[1] == colorSpaceOut->trc[1]
+                && colorSpaceIn->trc[2] == colorSpaceOut->trc[2];
+        }
+    } else {
+        if (colorSpaceIn && colorSpaceIn->transferFunction != QColorSpace::TransferFunction::Linear)
+            return false;
+        if (colorSpaceOut && colorSpaceOut->transferFunction != QColorSpace::TransferFunction::Linear)
+            return false;
+    }
+    return true;
+}
+
 QT_END_NAMESPACE
diff --git a/src/gui/painting/qcolortransform.h b/src/gui/painting/qcolortransform.h
index 3df5be7c8b..14673fe924 100644
--- a/src/gui/painting/qcolortransform.h
+++ b/src/gui/painting/qcolortransform.h
@@ -31,16 +31,21 @@ public:
     QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QColorTransform)
 
     void swap(QColorTransform &other) noexcept { d.swap(other.d); }
+    Q_GUI_EXPORT bool isIdentity() const noexcept;
 
     Q_GUI_EXPORT QRgb map(QRgb argb) const;
     Q_GUI_EXPORT QRgba64 map(QRgba64 rgba64) const;
     Q_GUI_EXPORT QColor map(const QColor &color) const;
 
+    friend bool operator==(const QColorTransform &ct1, const QColorTransform &ct2)
+    { return ct1.compare(ct2); }
+    friend bool operator!=(const QColorTransform &ct1, const QColorTransform &ct2)
+    { return !ct1.compare(ct2); }
+
 private:
-    friend class QColorSpace;
     friend class QColorSpacePrivate;
     friend class QColorTransformPrivate;
-    friend class QImage;
+    Q_GUI_EXPORT bool compare(const QColorTransform &other) const;
 
     QExplicitlySharedDataPointer<QColorTransformPrivate> d;
 };
diff --git a/src/gui/painting/qcolortransform_p.h b/src/gui/painting/qcolortransform_p.h
index 36420dcfdc..c3063c0fc6 100644
--- a/src/gui/painting/qcolortransform_p.h
+++ b/src/gui/painting/qcolortransform_p.h
@@ -36,6 +36,7 @@ public:
     void updateLutsIn() const;
     void updateLutsOut() const;
     bool simpleGammaCorrection() const;
+    bool isIdentity() const;
 
     void prepare();
     enum TransformFlag {