core/colorspace: be more robust about edge cases

xyz -> xy and xy -> xyz conversions have divisions in them, so we need to
handle the edge cases of the divisor being zero. This can happen if an ICC
profile is invalid, or if the XYZ color space is used.

autotests/test_colorspaces.cpp

@@ -21,7 +21,7 @@ public:
 private Q_SLOTS:
     void roundtripConversion_data();
     void roundtripConversion();
-    void nonNormalizedPrimaries();
+    void testXYZ_XYconversions();
     void testIdentityTransformation_data();
     void testIdentityTransformation();
     void testColorPipeline_data();
@@ -82,16 +82,14 @@ void TestColorspaces::roundtripConversion()
     }
 }
 
-void TestColorspaces::nonNormalizedPrimaries()
+void TestColorspaces::testXYZ_XYconversions()
 {
-    // this test ensures that non-normalized primaries don't mess up the transformations between color spaces
+    // this test ensures that Colorimetry::xyzToXY and Colorimetry::xyToXYZ can handle weird inputs
-    const auto &from = ColorDescription::sRGB;
+    // and don't cause crashes
-    const ColorDescription to(Colorimetry(Colorimetry::xyToXYZ(from.containerColorimetry().red()) * 2, Colorimetry::xyToXYZ(from.containerColorimetry().green()) * 2, Colorimetry::xyToXYZ(from.containerColorimetry().blue()) * 2, Colorimetry::xyToXYZ(from.containerColorimetry().white()) * 2), from.transferFunction(), from.referenceLuminance(), from.minLuminance(), from.maxAverageLuminance(), from.maxHdrLuminance());
+    QCOMPARE(Colorimetry::xyzToXY(QVector3D(0, 0, 0)), QVector2D(0, 0));
-
+    QCOMPARE_LE(Colorimetry::xyzToXY(QVector3D(100, 100, 100)).y(), 1);
-    const auto convertedWhite = from.toOther(to, RenderingIntent::RelativeColorimetric) * QVector3D(1, 1, 1);
+    QCOMPARE(Colorimetry::xyToXYZ(QVector2D(0, 0)), QVector3D(0, 1, 0));
-    QCOMPARE_LE(std::abs(1 - convertedWhite.x()), s_resolution10bit);
+    QCOMPARE(Colorimetry::xyToXYZ(QVector2D(1, 0)), QVector3D(1, 1, 0));
-    QCOMPARE_LE(std::abs(1 - convertedWhite.y()), s_resolution10bit);
-    QCOMPARE_LE(std::abs(1 - convertedWhite.z()), s_resolution10bit);
 }
 
 void TestColorspaces::testIdentityTransformation_data()

src/core/colorspace.cpp

@@ -28,12 +28,20 @@ static QMatrix4x4 matrixFromColumns(const QVector3D &first, const QVector3D &sec
 
 QVector3D Colorimetry::xyToXYZ(QVector2D xy)
 {
+    if (xy.y() == 0) {
+        // special case for XYZ Colorimetry
+        // where xy.y == 0 is valid
+        return QVector3D(xy.x(), 1, 0);
+    }
     return QVector3D(xy.x() / xy.y(), 1, (1 - xy.x() - xy.y()) / xy.y());
 }
 
 QVector2D Colorimetry::xyzToXY(QVector3D xyz)
 {
-    xyz /= xyz.y();
+    if (xyz.y() == 0) {
+        // this is nonsense, but at least doesn't crash
+        return QVector2D(0, 0);
+    }
     return QVector2D(xyz.x() / (xyz.x() + xyz.y() + xyz.z()), xyz.y() / (xyz.x() + xyz.y() + xyz.z()));
 }
 
@@ -76,11 +84,6 @@ QMatrix4x4 Colorimetry::chromaticAdaptationMatrix(QVector2D sourceWhitepoint, QV
     return inverseBradford * adaptation * bradford;
 }
 
-static QVector3D normalizeToY1(const QVector3D &vect)
-{
-    return vect.y() == 0 ? vect : QVector3D(vect.x() / vect.y(), 1, vect.z() / vect.y());
-}
-
 QMatrix4x4 Colorimetry::calculateToXYZMatrix(QVector3D red, QVector3D green, QVector3D blue, QVector3D white)
 {
     const auto component_scale = (matrixFromColumns(red, green, blue)).inverted() * white;
@@ -107,16 +110,6 @@ Colorimetry::Colorimetry(QVector2D red, QVector2D green, QVector2D blue, QVector
 {
 }
 
-Colorimetry::Colorimetry(QVector3D red, QVector3D green, QVector3D blue, QVector3D white)
-    : m_red(xyzToXY(red))
-    , m_green(xyzToXY(green))
-    , m_blue(xyzToXY(blue))
-    , m_white(xyzToXY(white))
-    , m_toXYZ(calculateToXYZMatrix(normalizeToY1(red), normalizeToY1(green), normalizeToY1(blue), normalizeToY1(white)))
-    , m_fromXYZ(m_toXYZ.inverted())
-{
-}
-
 const QMatrix4x4 &Colorimetry::toXYZ() const
 {
     return m_toXYZ;

src/core/colorspace.h

@@ -68,7 +68,6 @@ public:
     static QMatrix4x4 calculateToXYZMatrix(QVector3D red, QVector3D green, QVector3D blue, QVector3D white);
 
     explicit Colorimetry(QVector2D red, QVector2D green, QVector2D blue, QVector2D white);
-    explicit Colorimetry(QVector3D red, QVector3D green, QVector3D blue, QVector3D white);
 
     /**
      * @returns a matrix that transforms from the linear RGB representation of colors in this colorimetry to the XYZ representation

src/core/iccprofile.cpp

@@ -263,11 +263,15 @@ std::unique_ptr<IccProfile> IccProfile::load(const QString &path)
         qCWarning(KWIN_CORE, "profile is missing the wtpt tag");
         return nullptr;
     }
+    if (whitepoint->Y == 0) {
+        qCWarning(KWIN_CORE, "profile has a zero luminance whitepoint");
+        return nullptr;
+    }
 
-    QVector3D red;
+    QVector2D red;
-    QVector3D green;
+    QVector2D green;
-    QVector3D blue;
+    QVector2D blue;
-    QVector3D white(whitepoint->X, whitepoint->Y, whitepoint->Z);
+    QVector2D white = Colorimetry::xyzToXY(QVector3D(whitepoint->X, whitepoint->Y, whitepoint->Z));
     std::optional<QMatrix4x4> chromaticAdaptationMatrix;
     if (cmsIsTag(handle, cmsSigChromaticAdaptationTag)) {
         // the chromatic adaptation tag is a 3x3 matrix that converts from the actual whitepoint to D50
@@ -284,12 +288,12 @@ std::unique_ptr<IccProfile> IccProfile::load(const QString &path)
             return nullptr;
         }
         const QVector3D D50(0.9642, 1.0, 0.8249);
-        white = *chromaticAdaptationMatrix * D50;
+        white = Colorimetry::xyzToXY(*chromaticAdaptationMatrix * D50);
     }
     if (cmsCIExyYTRIPLE *chrmTag = static_cast<cmsCIExyYTRIPLE *>(cmsReadTag(handle, cmsSigChromaticityTag))) {
-        red = Colorimetry::xyToXYZ(QVector2D(chrmTag->Red.x, chrmTag->Red.y)) * chrmTag->Red.Y;
+        red = QVector2D(chrmTag->Red.x, chrmTag->Red.y);
-        green = Colorimetry::xyToXYZ(QVector2D(chrmTag->Green.x, chrmTag->Green.y)) * chrmTag->Green.Y;
+        green = QVector2D(chrmTag->Green.x, chrmTag->Green.y);
-        blue = Colorimetry::xyToXYZ(QVector2D(chrmTag->Blue.x, chrmTag->Blue.y)) * chrmTag->Blue.Y;
+        blue = QVector2D(chrmTag->Blue.x, chrmTag->Blue.y);
     } else {
         const cmsCIEXYZ *r = static_cast<cmsCIEXYZ *>(cmsReadTag(handle, cmsSigRedColorantTag));
         const cmsCIEXYZ *g = static_cast<cmsCIEXYZ *>(cmsReadTag(handle, cmsSigGreenColorantTag));
@@ -299,9 +303,9 @@ std::unique_ptr<IccProfile> IccProfile::load(const QString &path)
             return nullptr;
         }
         if (chromaticAdaptationMatrix) {
-            red = *chromaticAdaptationMatrix * QVector3D(r->X, r->Y, r->Z);
+            red = Colorimetry::xyzToXY(*chromaticAdaptationMatrix * QVector3D(r->X, r->Y, r->Z));
-            green = *chromaticAdaptationMatrix * QVector3D(g->X, g->Y, g->Z);
+            green = Colorimetry::xyzToXY(*chromaticAdaptationMatrix * QVector3D(g->X, g->Y, g->Z));
-            blue = *chromaticAdaptationMatrix * QVector3D(b->X, b->Y, b->Z);
+            blue = Colorimetry::xyzToXY(*chromaticAdaptationMatrix * QVector3D(b->X, b->Y, b->Z));
         } else {
             // if the chromatic adaptation tag isn't available, fall back to using the media whitepoint instead
             cmsCIEXYZ adaptedR{};
@@ -313,9 +317,9 @@ std::unique_ptr<IccProfile> IccProfile::load(const QString &path)
             if (!success) {
                 return nullptr;
             }
-            red = QVector3D(adaptedR.X, adaptedR.Y, adaptedR.Z);
+            red = Colorimetry::xyzToXY(QVector3D(adaptedR.X, adaptedR.Y, adaptedR.Z));
-            green = QVector3D(adaptedG.X, adaptedG.Y, adaptedG.Z);
+            green = Colorimetry::xyzToXY(QVector3D(adaptedG.X, adaptedG.Y, adaptedG.Z));
-            blue = QVector3D(adaptedB.X, adaptedB.Y, adaptedB.Z);
+            blue = Colorimetry::xyzToXY(QVector3D(adaptedB.X, adaptedB.Y, adaptedB.Z));
         }
     }