Prepare for replacing Qt::Appearance with Qt::ColorScheme

Based on discussions in the 6.5 API review, where we concluded that
'appearance' is too general. Instead, we follow the CSS standard
and use the term 'color scheme'.

This patch is a first step, only introducing the new API, so that
submodules can port over. The next step will be to remove the old
API and transition the docs and platform themes.

Pick-to: 6.5
Change-Id: I43cdb6bb1ccb49c535c06b1897821467fd83ca60
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

src/corelib/global/qnamespace.h

@@ -52,6 +52,12 @@ namespace Qt {
         Dark,
     };
 
+    enum class ColorScheme {
+        Unknown,
+        Light,
+        Dark,
+    };
+
     enum MouseButton {
         NoButton         = 0x00000000,
         LeftButton       = 0x00000001,
@@ -1758,6 +1764,7 @@ namespace Qt {
     Q_ENUM_NS(CursorShape)
     Q_ENUM_NS(GlobalColor)
     Q_ENUM_NS(Appearance)
+    Q_ENUM_NS(ColorScheme)
     Q_ENUM_NS(AspectRatioMode)
     Q_ENUM_NS(TransformationMode)
     Q_FLAG_NS(ImageConversionFlags)

src/gui/kernel/qguiapplication.cpp

@@ -2611,6 +2611,12 @@ Qt::Appearance QGuiApplicationPrivate::appearance()
                            : Qt::Appearance::Unknown;
 }
 
+Qt::ColorScheme QGuiApplicationPrivate::colorScheme()
+{
+    return platformTheme() ? platformTheme()->colorScheme()
+                           : Qt::ColorScheme::Unknown;
+}
+
 void QGuiApplicationPrivate::handleThemeChanged()
 {
     updatePalette();

src/gui/kernel/qguiapplication_p.h

@@ -314,6 +314,7 @@ private:
     friend class QDragManager;
 
     static Qt::Appearance appearance();
+    static Qt::ColorScheme colorScheme();
 
     static QGuiApplicationPrivate *self;
     static int m_fakeMouseSourcePointId;

src/gui/kernel/qplatformtheme.cpp

@@ -441,6 +441,11 @@ Qt::Appearance QPlatformTheme::appearance() const
     return Qt::Appearance::Unknown;
 }
 
+Qt::ColorScheme QPlatformTheme::colorScheme() const
+{
+    return Qt::ColorScheme(appearance());
+}
+
 const QPalette *QPlatformTheme::palette(Palette type) const
 {
     Q_D(const QPlatformTheme);

src/gui/kernel/qplatformtheme.h

@@ -295,6 +295,7 @@ public:
 #endif
 
     virtual Qt::Appearance appearance() const;
+    virtual Qt::ColorScheme colorScheme() const;
 
     virtual const QPalette *palette(Palette type = SystemPalette) const;
 

src/gui/kernel/qstylehints.cpp

@@ -133,6 +133,11 @@ Qt::Appearance QStyleHints::appearance() const
     return d->appearance();
 }
 
+Qt::ColorScheme QStyleHints::colorScheme() const
+{
+    return Qt::ColorScheme(appearance());
+}
+
 /*!
     Sets the \a mousePressAndHoldInterval.
     \internal

src/gui/kernel/qstylehints.h

@@ -53,6 +53,7 @@ class Q_GUI_EXPORT QStyleHints : public QObject
                FINAL)
     Q_PROPERTY(int touchDoubleTapDistance READ touchDoubleTapDistance STORED false CONSTANT FINAL)
     Q_PROPERTY(Qt::Appearance appearance READ appearance NOTIFY appearanceChanged FINAL)
+    Q_PROPERTY(Qt::ColorScheme colorScheme READ colorScheme NOTIFY colorSchemeChanged FINAL)
 
 public:
     void setMouseDoubleClickInterval(int mouseDoubleClickInterval);
@@ -94,6 +95,7 @@ public:
     void setMouseQuickSelectionThreshold(int threshold);
     int mouseQuickSelectionThreshold() const;
     Qt::Appearance appearance() const;
+    Qt::ColorScheme colorScheme() const;
 
 Q_SIGNALS:
     void cursorFlashTimeChanged(int cursorFlashTime);
@@ -108,6 +110,7 @@ Q_SIGNALS:
     void wheelScrollLinesChanged(int scrollLines);
     void mouseQuickSelectionThresholdChanged(int threshold);
     void appearanceChanged(Qt::Appearance appearance);
+    void colorSchemeChanged(Qt::ColorScheme colorScheme);
 
 private:
     friend class QGuiApplication;