Fix drag and drop for Xcb

Make the xcb plugin work in native coordinates, using platform windows as
much as possible. As part of this, replace QMouseEvent in QBasicDrag with
just a QPoint. This is private API, so we can change this without warning.

In addition to xcb, QBasicDrag is used in QSimpleDrag and for Wayland.
QSimpleDrag does not yet have a fix for highDpi, but it should continue
working in the non-scaled case. Wayland (and any other module which uses
QBasicDrag) will need a compile fix.

Also fix bug in QWindowSystemInterface: handleDrag()/handleDrop()
take positions in window local coordinates, not global.

Change-Id: I86543e4f52a7b3ba1efeac815cf89bbd97c0a0a2
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>

4 files changed, 44 insertions, 20 deletions

diff --git a/src/gui/kernel/qhighdpiscaling_p.h b/src/gui/kernel/qhighdpiscaling_p.h
index 827c21ad5c..6c96fa2e07 100644
--- a/src/gui/kernel/qhighdpiscaling_p.h
+++ b/src/gui/kernel/qhighdpiscaling_p.h
@@ -171,6 +171,18 @@ inline QRect fromNativeScreenGeometry(const QRect &nativeScreenGeometry, const Q
     return QRect(nativeScreenGeometry.topLeft(), fromNative(nativeScreenGeometry.size(), QHighDpiScaling::factor(screen)));
 }
 
+inline QPoint fromNativeLocalPosition(const QPoint &pos, const QWindow *window)
+{
+    const qreal scaleFactor = QHighDpiScaling::factor(window);
+    return pos / scaleFactor;
+}
+
+inline QPoint toNativeLocalPosition(const QPoint &pos, const QWindow *window)
+{
+    const qreal scaleFactor = QHighDpiScaling::factor(window);
+    return pos * scaleFactor;
+}
+
 inline QPointF fromNativeLocalPosition(const QPointF &pos, const QWindow *window)
 {
     const qreal scaleFactor = QHighDpiScaling::factor(window);
diff --git a/src/gui/kernel/qsimpledrag.cpp b/src/gui/kernel/qsimpledrag.cpp
index 090e88c118..517f3024aa 100644
--- a/src/gui/kernel/qsimpledrag.cpp
+++ b/src/gui/kernel/qsimpledrag.cpp
@@ -55,6 +55,7 @@
 #include <private/qdnd_p.h>
 
 #include <private/qshapedpixmapdndwindow_p.h>
+#include <private/qhighdpiscaling_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -106,6 +107,12 @@ void QBasicDrag::disableEventFilter()
     qApp->removeEventFilter(this);
 }
 
+
+static inline QPoint getNativeMousePos(QEvent *e, QObject *o)
+{
+    return QHighDpi::toNativePixels(static_cast<QMouseEvent *>(e)->globalPos(), qobject_cast<QWindow*>(o));
+}
+
 bool QBasicDrag::eventFilter(QObject *o, QEvent *e)
 {
     Q_UNUSED(o);
@@ -139,19 +146,21 @@ bool QBasicDrag::eventFilter(QObject *o, QEvent *e)
         }
 
         case QEvent::MouseMove:
-            move(static_cast<QMouseEvent *>(e));
+        {
+            QPoint nativePosition = getNativeMousePos(e, o);
+            move(nativePosition);
             return true; // Eat all mouse events
-
+        }
         case QEvent::MouseButtonRelease:
             disableEventFilter();
             if (canDrop()) {
-                drop(static_cast<QMouseEvent *>(e));
+                QPoint nativePosition = getNativeMousePos(e, o);
+                drop(nativePosition);
             } else {
                 cancel();
             }
             exitDndEventLoop();
             return true; // Eat all mouse events
-
         case QEvent::MouseButtonPress:
         case QEvent::MouseButtonDblClick:
         case QEvent::Wheel:
@@ -218,13 +227,13 @@ void QBasicDrag::cancel()
     m_drag_icon_window->setVisible(false);
 }
 
-void QBasicDrag::move(const QMouseEvent *)
+void QBasicDrag::move(const QPoint &)
 {
     if (m_drag)
         m_drag_icon_window->updateGeometry();
 }
 
-void QBasicDrag::drop(const QMouseEvent *)
+void QBasicDrag::drop(const QPoint &)
 {
     disableEventFilter();
     restoreCursor();
@@ -321,14 +330,15 @@ void QSimpleDrag::cancel()
     }
 }
 
-void QSimpleDrag::move(const QMouseEvent *me)
+void QSimpleDrag::move(const QPoint &globalPos)
 {
-    QBasicDrag::move(me);
-    QWindow *window = topLevelAt(me->globalPos());
+    //### not high-DPI aware
+    QBasicDrag::move(globalPos);
+    QWindow *window = topLevelAt(globalPos);
     if (!window)
         return;
 
-    const QPoint pos = me->globalPos() - window->geometry().topLeft();
+    const QPoint pos = globalPos - window->geometry().topLeft();
     const QPlatformDragQtResponse qt_response =
         QWindowSystemInterface::handleDrag(window, drag()->mimeData(), pos, drag()->supportedActions());
 
@@ -336,14 +346,16 @@ void QSimpleDrag::move(const QMouseEvent *me)
     setCanDrop(qt_response.isAccepted());
 }
 
-void QSimpleDrag::drop(const QMouseEvent *me)
+void QSimpleDrag::drop(const QPoint &globalPos)
 {
-    QBasicDrag::drop(me);
-    QWindow *window = topLevelAt(me->globalPos());
+    //### not high-DPI aware
+
+    QBasicDrag::drop(globalPos);
+    QWindow *window = topLevelAt(globalPos);
     if (!window)
         return;
 
-    const QPoint pos = me->globalPos() - window->geometry().topLeft();
+    const QPoint pos = globalPos - window->geometry().topLeft();
     const QPlatformDropQtResponse response =
             QWindowSystemInterface::handleDrop(window, drag()->mimeData(),pos, drag()->supportedActions());
     if (response.isAccepted()) {
diff --git a/src/gui/kernel/qsimpledrag_p.h b/src/gui/kernel/qsimpledrag_p.h
index 7812f8b863..728ae7bd15 100644
--- a/src/gui/kernel/qsimpledrag_p.h
+++ b/src/gui/kernel/qsimpledrag_p.h
@@ -73,8 +73,8 @@ protected:
 
     virtual void startDrag();
     virtual void cancel();
-    virtual void move(const QMouseEvent *me);
-    virtual void drop(const QMouseEvent *me);
+    virtual void move(const QPoint &globalPos) = 0;
+    virtual void drop(const QPoint &globalPos) = 0;
     virtual void endDrag();
 
     QShapedPixmapWindow *shapedPixmapWindow() const { return m_drag_icon_window; }
@@ -111,8 +111,8 @@ public:
 protected:
     virtual void startDrag() Q_DECL_OVERRIDE;
     virtual void cancel() Q_DECL_OVERRIDE;
-    virtual void move(const QMouseEvent *me) Q_DECL_OVERRIDE;
-    virtual void drop(const QMouseEvent *me) Q_DECL_OVERRIDE;
+    virtual void move(const QPoint &globalPos) Q_DECL_OVERRIDE;
+    virtual void drop(const QPoint &globalPos) Q_DECL_OVERRIDE;
 
 private:
     QWindow *m_current_window;
diff --git a/src/gui/kernel/qwindowsysteminterface.cpp b/src/gui/kernel/qwindowsysteminterface.cpp
index 13cbf5b8b6..13461e981e 100644
--- a/src/gui/kernel/qwindowsysteminterface.cpp
+++ b/src/gui/kernel/qwindowsysteminterface.cpp
@@ -651,12 +651,12 @@ int QWindowSystemInterface::windowSystemEventsQueued()
 #ifndef QT_NO_DRAGANDDROP
 QPlatformDragQtResponse QWindowSystemInterface::handleDrag(QWindow *w, const QMimeData *dropData, const QPoint &p, Qt::DropActions supportedActions)
 {
-    return QGuiApplicationPrivate::processDrag(w, dropData, QHighDpi::fromNativePixels(p, w),supportedActions);
+    return QGuiApplicationPrivate::processDrag(w, dropData, QHighDpi::fromNativeLocalPosition(p, w) ,supportedActions);
 }
 
 QPlatformDropQtResponse QWindowSystemInterface::handleDrop(QWindow *w, const QMimeData *dropData, const QPoint &p, Qt::DropActions supportedActions)
 {
-    return QGuiApplicationPrivate::processDrop(w, dropData, QHighDpi::fromNativePixels(p, w),supportedActions);
+    return QGuiApplicationPrivate::processDrop(w, dropData, QHighDpi::fromNativeLocalPosition(p, w),supportedActions);
 }
 #endif // QT_NO_DRAGANDDROP