File 0001-QSimpleDrag-Fix-mouse-release-coords-for-delayed-eve.patch of Package libqt5-qtbase.16540

From 4a7771f206d4b29be549d3827c36a46679d90de6 Mon Sep 17 00:00:00 2001
From: Eike Hein <hein@kde.org>
Date: Sun, 7 Jan 2018 13:02:01 +0900
Subject: [PATCH] QSimpleDrag: Fix mouse release coords for delayed event
 transmission

On platforms such as XCB, the drag cursor pixmap is shown via a window
(a QShapedPixmapWindow) under the cursor.

The mouse button release event at the end of the drag is received in
this QXcbWindow, but intercepted by an event filter that QSimpleDrag
installs on the QApplication. It then resends it unmodified(!) after
the drag has ended and the drag pixmap window destroyed, causing it to
be delivered to the new top-level window.

The local coordinates in the unmodified QMouseEvent are local to the
drag pixmap window and don't match the window it is delayed-transmitted
to.

This ends up having fatal, user-visible effects particularly in Qt
Quick: QQuickWindow synthesizes a hover event once per frame using
the last received mouse coordinates, here: the release posted by
QSimpleDrag. This is done to update the hover event state for items
under the cursor when the mouse hasn't moved (e.g. QQuickMouseArea::
containsMouse). The bogus event coordinates in the release event then
usually end up causing an item near the top-left of the QQuickWindow
to assume it is hovered (because drag pixmap windows tend to be small),
even when the mouse cursor is actually far away from it at the end of
the drag.

This shows up e.g. in the Plasma 5 desktop, where dragging an icon
on the desktop will cause the icon at the top-left of the screen (if
any) to switch to hovered state, as the release coordinates on the
drag pixmap window (showing a dragged icon) fall into the geometry
of the top-left icon.

QSimpleDrag contains a topLevelAt() function to find the top-level
window under the global cursor coordinates that is not the drag
pixmap window. This is used by the drop event delivery code.

This patch uses this function to find the relevant top-level window,
then asks it to map the global cusor coordinates to its local
coordinate system, then synthesizes a new QMouseEvent with local
coordinates computed in this fashion. As a result the window now
gets a release event with coordinates that make sense and are
correct.

Task-number: QTBUG-66103
Change-Id: I04ebe6ccd4a991fdd4b540ff0227973ea8896a9d
Reviewed-by: Eike Hein <hein@kde.org>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
---
 src/gui/kernel/qsimpledrag.cpp | 32 +++++++++++++++++++++++++++-----
 src/gui/kernel/qsimpledrag_p.h |  6 +++---
 2 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/src/gui/kernel/qsimpledrag.cpp b/src/gui/kernel/qsimpledrag.cpp
index a1e25dc53c..87d3ba5915 100644
--- a/src/gui/kernel/qsimpledrag.cpp
+++ b/src/gui/kernel/qsimpledrag.cpp
@@ -58,6 +58,7 @@
 
 #include <QtCore/QEventLoop>
 #include <QtCore/QDebug>
+#include <QtCore/QLoggingCategory>
 
 #include <private/qguiapplication_p.h>
 #include <private/qdnd_p.h>
@@ -69,6 +70,8 @@ QT_BEGIN_NAMESPACE
 
 #ifndef QT_NO_DRAGANDDROP
 
+Q_LOGGING_CATEGORY(lcDnd, "qt.gui.dnd")
+
 static QWindow* topLevelAt(const QPoint &pos)
 {
     QWindowList list = QGuiApplication::topLevelWindows();
@@ -94,10 +97,10 @@ static QWindow* topLevelAt(const QPoint &pos)
 */
 
 QBasicDrag::QBasicDrag() :
-    m_restoreCursor(false), m_eventLoop(0),
+    m_current_window(nullptr), m_restoreCursor(false), m_eventLoop(nullptr),
     m_executed_drop_action(Qt::IgnoreAction), m_can_drop(false),
-    m_drag(0), m_drag_icon_window(0), m_useCompositing(true),
-    m_screen(Q_NULLPTR)
+    m_drag(nullptr), m_drag_icon_window(nullptr), m_useCompositing(true),
+    m_screen(nullptr)
 {
 }
 
@@ -161,6 +164,7 @@ bool QBasicDrag::eventFilter(QObject *o, QEvent *e)
             return true; // Eat all mouse move events
         }
         case QEvent::MouseButtonRelease:
+        {
             disableEventFilter();
             if (canDrop()) {
                 QPoint nativePosition = getNativeMousePos(e, m_drag_icon_window);
@@ -169,8 +173,25 @@ bool QBasicDrag::eventFilter(QObject *o, QEvent *e)
                 cancel();
             }
             exitDndEventLoop();
-            QCoreApplication::postEvent(o, new QMouseEvent(*static_cast<QMouseEvent *>(e)));
+
+            // If a QShapedPixmapWindow (drag feedback) is being dragged along, the
+            // mouse event's localPos() will be relative to that, which is useless.
+            // We want a position relative to the window where the drag ends, if possible (?).
+            // If there is no such window (belonging to this Qt application),
+            // make the event relative to the window where the drag started. (QTBUG-66103)
+            const QMouseEvent *release = static_cast<QMouseEvent *>(e);
+            const QWindow *releaseWindow = topLevelAt(release->globalPos());
+            qCDebug(lcDnd) << "mouse released over" << releaseWindow << "after drag from" << m_current_window << "globalPos" << release->globalPos();
+            if (!releaseWindow)
+                releaseWindow = m_current_window;
+            QPoint releaseWindowPos = (releaseWindow ? releaseWindow->mapFromGlobal(release->globalPos()) : release->globalPos());
+            QMouseEvent *newRelease = new QMouseEvent(release->type(),
+                releaseWindowPos, releaseWindowPos, release->screenPos(),
+                release->button(), release->buttons(),
+                release->modifiers(), release->source());
+            QCoreApplication::postEvent(o, newRelease);
             return true; // defer mouse release events until drag event loop has returned
+        }
         case QEvent::MouseButtonDblClick:
         case QEvent::Wheel:
             return true;
@@ -349,7 +370,7 @@ static inline QPoint fromNativeGlobalPixels(const QPoint &point)
     into account.
 */
 
-QSimpleDrag::QSimpleDrag() : m_current_window(0)
+QSimpleDrag::QSimpleDrag()
 {
 }
 
@@ -373,6 +394,7 @@ void QSimpleDrag::startDrag()
         updateCursor(Qt::IgnoreAction);
     }
     setExecutedDropAction(Qt::IgnoreAction);
+    qCDebug(lcDnd) << "drag began from" << m_current_window<< "cursor pos" << QCursor::pos() << "can drop?" << canDrop();
 }
 
 void QSimpleDrag::cancel()
diff --git a/src/gui/kernel/qsimpledrag_p.h b/src/gui/kernel/qsimpledrag_p.h
index 0b8a0bc703..bbd7f7f4bb 100644
--- a/src/gui/kernel/qsimpledrag_p.h
+++ b/src/gui/kernel/qsimpledrag_p.h
@@ -105,6 +105,9 @@ protected:
 
     QDrag *drag() const { return m_drag; }
 
+protected:
+    QWindow *m_current_window;
+
 private:
     void enableEventFilter();
     void disableEventFilter();
@@ -132,9 +135,6 @@ protected:
     virtual void cancel() 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;
 };
 
 #endif // QT_NO_DRAGANDDROP
-- 
2.16.1
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