Add QColorSpace::isValidTarget

To indicate color spaces that can not be used as a target,
but only as a source.

Change-Id: Iae79e3533599c112872d171a2f45178029be89dc
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

src/gui/image/qimage.cpp

@@ -5018,7 +5018,7 @@ void QImage::convertToColorSpace(const QColorSpace &colorSpace)
         return;
     if (!d->colorSpace.isValid())
         return;
-    if (!colorSpace.isValid()) {
+    if (!colorSpace.isValidTarget()) {
         qWarning() << "QImage::convertToColorSpace: Output colorspace is not valid";
         return;
     }
@@ -5039,8 +5039,14 @@ void QImage::convertToColorSpace(const QColorSpace &colorSpace)
 */
 QImage QImage::convertedToColorSpace(const QColorSpace &colorSpace) const
 {
-    if (!d || !d->colorSpace.isValid() || !colorSpace.isValid())
+    if (!d)
         return QImage();
+    if (!d->colorSpace.isValid())
+        return QImage();
+    if (!colorSpace.isValidTarget()) {
+        qWarning() << "QImage::convertedToColorSpace: Output colorspace is not valid";
+        return QImage();
+    }
     if (d->colorSpace == colorSpace)
         return *this;
     QImage image = copy();

src/gui/painting/qcolorspace.cpp

@@ -544,12 +544,14 @@ void QColorSpacePrivate::clearElementListProcessingForEdit()
 
     Defines the processing model used for color space transforms.
 
-    \value ThreeComponentMatrix The transform consist of a matrix calculated from primaries and set of transfer functions for each color channel.
+    \value ThreeComponentMatrix The transform consist of a matrix calculated from primaries and set of transfer functions
-    This is very fast and used by all predefined color spaces.
+    for each color channel. This is very fast and used by all predefined color spaces. Any color space on this form is
-    \value ElementListProcessing The transforms are two lists of processing elements that can do many things,
+    reversible and always both valid sources and targets.
+    \value ElementListProcessing The transforms are one or two lists of processing elements that can do many things,
     each list only process either to the connection color space or from it. This is very flexible, but rather
-    slow, and can only be set by reading ICC profiles (See  \l fromIccProfile()). When changing either primaries
+    slow, and can only be set by reading ICC profiles (See  \l fromIccProfile()). Since the two lists are
-     or transfer function on a color space on this type it will reset to a ThreeComponentMatrix form.
+    separate a color space on this form can be a valid source, but not necessarily also a valid target. When changing
+    either primaries or transfer function on a color space on this type it will reset to an empty ThreeComponentMatrix form.
 */
 
 /*!
@@ -968,7 +970,12 @@ QColorSpace QColorSpace::fromIccProfile(const QByteArray &iccProfile)
 }
 
 /*!
-    Returns \c true if the color space is valid.
+    Returns \c true if the color space is valid. For a color space with \c TransformModel::ThreeComponentMatrix
+    that means both primaries and transfer functions set, and implies isValidTarget().
+    For a color space with \c TransformModel::ElementListProcessing it means it has a valid source transform, to
+    check if it also a valid target color space use isValidTarget().
+
+    \sa isValidTarget()
 */
 bool QColorSpace::isValid() const noexcept
 {
@@ -977,6 +984,20 @@ bool QColorSpace::isValid() const noexcept
     return d_ptr->isValid();
 }
 
+/*!
+    \since 6.8
+
+    Returns \c true if the color space is a valid target color space.
+*/
+bool QColorSpace::isValidTarget() const noexcept
+{
+    if (!d_ptr)
+        return false;
+    if (!d_ptr->isThreeComponentMatrix())
+        return !d_ptr->mBA.isEmpty();
+    return d_ptr->isValid();
+}
+
 /*!
     \internal
 */
@@ -1148,13 +1169,13 @@ bool QColorSpacePrivate::equals(const QColorSpacePrivate *other) const
 */
 QColorTransform QColorSpace::transformationToColorSpace(const QColorSpace &colorspace) const
 {
-    if (!isValid() || !colorspace.isValid())
+    if (!isValid())
         return QColorTransform();
 
     if (*this == colorspace)
         return QColorTransform();
-    if (colorspace.transformModel() == TransformModel::ElementListProcessing && colorspace.d_ptr->mBA.isEmpty()) {
+    if (!colorspace.isValidTarget()) {
-        qWarning() << "Attempted transform to from-only colorspace";
+        qWarning() << "QColorSpace::transformationToColorSpace: colorspace not a valid target";
         return QColorTransform();
     }
 

src/gui/painting/qcolorspace.h

@@ -108,6 +108,7 @@ public:
     TransformModel transformModel() const noexcept;
     void detach();
     bool isValid() const noexcept;
+    bool isValidTarget() const noexcept;
 
     friend inline bool operator==(const QColorSpace &colorSpace1, const QColorSpace &colorSpace2)
     { return colorSpace1.equals(colorSpace2); }

tests/auto/gui/painting/qcolorspace/tst_qcolorspace.cpp

@@ -558,7 +558,7 @@ void tst_QColorSpace::imageConversionOverNonThreeComponentMatrix()
     QFETCH(QColorSpace, fromColorSpace);
     QFETCH(QColorSpace, toColorSpace);
     QVERIFY(fromColorSpace.isValid());
-    QVERIFY(toColorSpace.isValid());
+    QVERIFY(toColorSpace.isValidTarget());
 
     QVERIFY(!fromColorSpace.transformationToColorSpace(toColorSpace).isIdentity());
 

tests/libfuzzer/gui/painting/qcolorspace/fromiccprofile/main.cpp

@@ -25,11 +25,15 @@ extern "C" int LLVMFuzzerTestOneInput(const char *data, size_t size) {
         QColorSpace cs2 = cs;
         cs2.setDescription("Hello");
         bool b = (cs == cs2);
+        Q_UNUSED(b);
         QRgb color = 0xfaf8fa00;
         color = trans1.map(color);
+        if (cs.isValidTarget()) {
             QColorTransform trans2 = QColorSpace(QColorSpace::SRgb).transformationToColorSpace(cs);
             bool a = (trans1 == trans2);
+            Q_UNUSED(a);
             color = trans2.map(color);
         }
+    }
     return 0;
 }