input: Introduce a outputArea property for tablet devices

It's important for tablet devices to be able to specify to which section
of the display we'll be fitting the tablet. This setting allows to
specify this by providing some options that will do so relative to the
output size.

CCBUG: 433045

autotests/libinput/mock_libinput.cpp

@@ -967,3 +967,23 @@ libinput_device_get_user_data(struct libinput_device *device)
 {
     return device->userData;
 }
+
+double
+libinput_event_tablet_tool_get_x_transformed(struct libinput_event_tablet_tool *event,
+                                             uint32_t width)
+{
+    Q_UNUSED(event)
+    Q_UNUSED(width)
+
+    // it's unused at the moment, it doesn't really matter what we return
+    return 0;
+}
+
+double
+libinput_event_tablet_tool_get_y_transformed(struct libinput_event_tablet_tool *event,
+                                             uint32_t height)
+{
+    Q_UNUSED(event)
+    Q_UNUSED(height)
+    return 4;
+}

src/backends/libinput/device.cpp

@@ -95,7 +95,8 @@ enum class ConfigKey {
     ScrollFactor,
     Orientation,
     Calibration,
-    OutputName
+    OutputName,
+    OutputArea,
 };
 
 struct ConfigDataBase
@@ -201,7 +202,9 @@ static const QMap<ConfigKey, ConfigDataBase *> s_configData{
     {ConfigKey::ScrollFactor, new ConfigData<qreal>(QByteArrayLiteral("ScrollFactor"), &Device::setScrollFactor, &Device::scrollFactorDefault)},
     {ConfigKey::Orientation, new ConfigData<DeviceOrientation>{}},
     {ConfigKey::Calibration, new ConfigData<CalibrationMatrix>{}},
-    {ConfigKey::OutputName, new ConfigData<QString>(QByteArrayLiteral("OutputName"), &Device::setOutputName, &Device::defaultOutputName)}};
+    {ConfigKey::OutputName, new ConfigData<QString>(QByteArrayLiteral("OutputName"), &Device::setOutputName, &Device::defaultOutputName)},
+    {ConfigKey::OutputArea, new ConfigData<QRectF>(QByteArrayLiteral("OutputArea"), &Device::setOutputArea, &Device::defaultOutputArea)},
+};
 
 namespace
 {
@@ -706,5 +709,28 @@ void Device::setLeds(LEDs leds)
     }
 }
 
+bool Device::supportsOutputArea() const
+{
+    return m_tabletTool;
+}
+
+QRectF Device::defaultOutputArea() const
+{
+    return QRectF(0, 0, 1, 1);
+}
+
+QRectF Device::outputArea() const
+{
+    return m_outputArea;
+}
+
+void Device::setOutputArea(const QRectF &outputArea)
+{
+    if (m_outputArea != outputArea) {
+        m_outputArea = outputArea;
+        writeEntry(ConfigKey::OutputArea, m_outputArea);
+        Q_EMIT outputAreaChanged();
+    }
+}
 }
 }

src/backends/libinput/device.h

@@ -138,6 +138,10 @@ class KWIN_EXPORT Device : public InputDevice
     Q_PROPERTY(bool defaultClickMethodClickfinger READ defaultClickMethodClickfinger CONSTANT)
     Q_PROPERTY(bool clickMethodClickfinger READ isClickMethodClickfinger WRITE setClickMethodClickfinger NOTIFY clickMethodChanged)
 
+    Q_PROPERTY(bool supportsOutputArea READ supportsOutputArea CONSTANT)
+    Q_PROPERTY(QRectF defaultOutputArea READ defaultOutputArea CONSTANT)
+    Q_PROPERTY(QRectF outputArea READ outputArea WRITE setOutputArea NOTIFY outputAreaChanged)
+
 public:
     explicit Device(libinput_device *device, QObject *parent = nullptr);
     ~Device() override;
@@ -619,6 +623,11 @@ public:
     LEDs leds() const override;
     void setLeds(LEDs leds) override;
 
+    QRectF defaultOutputArea() const;
+    bool supportsOutputArea() const;
+    QRectF outputArea() const;
+    void setOutputArea(const QRectF &outputArea);
+
     /**
      * Gets the Device for @p native. @c null if there is no Device for @p native.
      */
@@ -643,6 +652,7 @@ Q_SIGNALS:
     void scrollButtonChanged();
     void scrollFactorChanged();
     void clickMethodChanged();
+    void outputAreaChanged();
 
 private:
     template<typename T>
@@ -729,6 +739,7 @@ private:
     enum libinput_config_click_method m_clickMethod;
 
     LEDs m_leds;
+    QRectF m_outputArea = QRectF(0, 0, 1, 1);
 };
 
 }

src/backends/libinput/events.cpp

@@ -368,6 +368,13 @@ TabletToolEvent::TabletToolEvent(libinput_event *event, libinput_event_type type
 {
 }
 
+QPointF TabletToolEvent::transformedPosition(const QSize &size) const
+{
+    const QRectF outputArea = device()->outputArea();
+    return {size.width() * outputArea.x() + libinput_event_tablet_tool_get_x_transformed(m_tabletToolEvent, size.width() * outputArea.width()),
+            size.height() * outputArea.y() + libinput_event_tablet_tool_get_y_transformed(m_tabletToolEvent, size.height() * outputArea.height())};
+}
+
 TabletToolButtonEvent::TabletToolButtonEvent(libinput_event *event, libinput_event_type type)
     : Event(event, type)
     , m_tabletToolEvent(libinput_event_get_tablet_tool_event(event))

src/backends/libinput/events.h

@@ -307,11 +307,7 @@ public:
         return state == LIBINPUT_TABLET_TOOL_PROXIMITY_STATE_IN;
     }
 
-    QPointF transformedPosition(const QSize &size) const
-    {
-        return {libinput_event_tablet_tool_get_x_transformed(m_tabletToolEvent, size.width()),
-                libinput_event_tablet_tool_get_y_transformed(m_tabletToolEvent, size.height())};
-    }
+    QPointF transformedPosition(const QSize &size) const;
 
     struct libinput_tablet_tool *tool()
     {