QHighDpi::fromNativePixels: use correct screen

Calls like
	QHighDpi::fromNativePixels(point, window)

would return device independent coordinates outside any
screen in cases where the window is spanning multiple
screens and the native point was not on the main screen.

Correct this by looking up the correct screen and use
its scale factor and origin when scaling coordinates.

Task-number: QTBUG-73231
Change-Id: I01a3a42f42121b8d9f4ced2bb0fb023d6ae6bfe7
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
 

2 files changed, 42 insertions, 45 deletions

diff --git a/src/gui/kernel/qhighdpiscaling.cpp b/src/gui/kernel/qhighdpiscaling.cpp
index 93fcb1a216..0fea416404 100644
--- a/src/gui/kernel/qhighdpiscaling.cpp
+++ b/src/gui/kernel/qhighdpiscaling.cpp
@@ -452,52 +452,30 @@ QDpi QHighDpiScaling::logicalDpi()
     return m_logicalDpi;
 }
 
-qreal QHighDpiScaling::factor(const QScreen *screen)
+QHighDpiScaling::ScaleAndOrigin QHighDpiScaling::scaleAndOrigin(const QPlatformScreen *platformScreen, QPoint *nativePosition)
 {
-    // Fast path for when scaling in Qt is not used at all.
     if (!m_active)
-        return qreal(1.0);
-
-    // The effective factor for a given screen is the product of the
-    // screen and global sub-factors
-    qreal factor = m_factor;
-    if (screen)
-        factor *= screenSubfactor(screen->handle());
-    return factor;
+        return { qreal(1), QPoint() };
+    const QPlatformScreen *actualScreen = nativePosition ?
+        platformScreen->screenForPosition(*nativePosition) : platformScreen;
+    return { m_factor * screenSubfactor(actualScreen), actualScreen->geometry().topLeft() };
 }
 
-qreal QHighDpiScaling::factor(const QPlatformScreen *platformScreen)
+QHighDpiScaling::ScaleAndOrigin QHighDpiScaling::scaleAndOrigin(const QScreen *screen, QPoint *nativePosition)
 {
     if (!m_active)
-        return qreal(1.0);
-
-    return m_factor * screenSubfactor(platformScreen);
+        return { qreal(1), QPoint() };
+    if (!screen)
+        return { m_factor, QPoint() }; // the global factor
+    return scaleAndOrigin(screen->handle(), nativePosition);
 }
 
-qreal QHighDpiScaling::factor(const QWindow *window)
+QHighDpiScaling::ScaleAndOrigin QHighDpiScaling::scaleAndOrigin(const QWindow *window, QPoint *nativePosition)
 {
     if (!m_active)
-        return qreal(1.0);
-
-    return factor(window ? window->screen() : QGuiApplication::primaryScreen());
-}
-
-QPoint QHighDpiScaling::origin(const QScreen *screen)
-{
-    return screen->geometry().topLeft();
-}
-
-QPoint QHighDpiScaling::origin(const QPlatformScreen *platformScreen)
-{
-    return platformScreen->geometry().topLeft();
-}
-
-QPoint QHighDpiScaling::origin(const QWindow *window)
-{
-    if (window && window->isTopLevel() && window->screen())
-        return window->screen()->geometry().topLeft();
-
-    return QPoint(0, 0);
+        return { qreal(1), QPoint() };
+    QScreen *screen = window ? window->screen() : QGuiApplication::primaryScreen();
+    return scaleAndOrigin(screen, nativePosition);
 }
 
 #endif //QT_NO_HIGHDPISCALING
diff --git a/src/gui/kernel/qhighdpiscaling_p.h b/src/gui/kernel/qhighdpiscaling_p.h
index 525e3fe78e..3410c1d345 100644
--- a/src/gui/kernel/qhighdpiscaling_p.h
+++ b/src/gui/kernel/qhighdpiscaling_p.h
@@ -78,14 +78,23 @@ public:
     static void setScreenFactor(QScreen *window, qreal factor);
 
     static bool isActive() { return m_active; }
-    static qreal factor(const QWindow *window);
-    static qreal factor(const QScreen *screen);
-    static qreal factor(const QPlatformScreen *platformScreen);
-    static QPoint origin(const QScreen *screen);
-    static QPoint origin(const QPlatformScreen *platformScreen);
-    static QPoint origin(const QWindow *window);
-    static QPoint mapPositionToNative(const QPoint &pos, const QPlatformScreen *platformScreen);
+
+    struct ScaleAndOrigin
+    {
+        qreal factor;
+        QPoint origin;
+    };
+    static ScaleAndOrigin scaleAndOrigin(const QPlatformScreen *platformScreen, QPoint *nativePosition = nullptr);
+    static ScaleAndOrigin scaleAndOrigin(const QScreen *screen, QPoint *nativePosition = nullptr);
+    static ScaleAndOrigin scaleAndOrigin(const QWindow *platformScreen, QPoint *nativePosition = nullptr);
+
+    template<typename C>
+    static qreal factor(C *context, QPoint *nativePosition = nullptr) {
+        return scaleAndOrigin(context, nativePosition).factor;
+    }
+
     static QPoint mapPositionFromNative(const QPoint &pos, const QPlatformScreen *platformScreen);
+    static QPoint mapPositionToNative(const QPoint &pos, const QPlatformScreen *platformScreen);
     static QPoint mapPositionToGlobal(const QPoint &pos, const QPoint &windowGlobalPosition, const QWindow *window);
     static QPoint mapPositionFromGlobal(const QPoint &pos, const QPoint &windowGlobalPosition, const QWindow *window);
     static QDpi logicalDpi();
@@ -166,16 +175,26 @@ inline QRegion scale(const QRegion &region, qreal scaleFactor, QPoint origin = Q
     return scaled;
 }
 
+template <typename T>
+inline QPoint position(T) { return QPoint(); }
+inline QPoint position(QPoint point) { return point; }
+inline QPoint position(QPointF point) { return point.toPoint(); }
+inline QPoint position(QRect rect) { return rect.center(); }
+inline QPoint position(QRectF rect) { return rect.center().toPoint(); }
+
 template <typename T, typename C>
 T fromNativePixels(const T &value, const C *context)
 {
-    return scale(value, qreal(1) / QHighDpiScaling::factor(context), QHighDpiScaling::origin(context));
+    QPoint nativePosition = position(value);
+    QHighDpiScaling::ScaleAndOrigin so = QHighDpiScaling::scaleAndOrigin(context, &nativePosition);
+    return scale(value, qreal(1) / so.factor, so.origin);
 }
 
 template <typename T, typename C>
 T toNativePixels(const T &value, const C *context)
 {
-    return scale(value, QHighDpiScaling::factor(context), QHighDpiScaling::origin(context));
+    QHighDpiScaling::ScaleAndOrigin so = QHighDpiScaling::scaleAndOrigin(context);
+    return scale(value, so.factor, so.origin);
 }
 
 template <typename T, typename C>