qpa: improve API to support DnDs from other processes

... instead of using a hack of directly accessing QGuiApplication
members.

The current QPA API was bad for two reasons:

1) It expects platform plugin authors to know about
internals of Qt Gui, particularly that QGuiApplication
uses QGuiApplication::{mouseButtons,keyboardModifiers}
to construct QDragMoveEvent and QDropEvent events. Which
results in the second reason why this is bad.

2) Platform plugins should not directly access member
variables of QGuiApplication, just to make sure that
QDragMoveEvent and QDropEvent events contain correct state.
Platform plugins should instead use QWindowSystemInterface
to communicate with Qt Gui (which is also the solution here).

The solution is to extend QWindowSystemInterface::handle{Drag,Drop}
to require mouse/keyboard state. We already do this for
some of the other methods, so it is nothing extraordinary.
This type of interface is also _required_ to support
drag-n-drops from other processes. We can't use
QGuiApplication::{mouseButtons,keyboardModifiers} when the
drag originates from another process, instead we need to
query mouse/keyboard state from the system.

This patch fixes drag-n-drops from others processes on XCB
platform plugin.

Task-number: QTBUG-57168
Change-Id: I3f8b0d2f76e9a32ae157622fef801829d629921d
Reviewed-by: Mikhail Svetkin <mikhail.svetkin@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 23 insertions, 14 deletions

diff --git a/src/plugins/platforms/xcb/qxcbdrag.cpp b/src/plugins/platforms/xcb/qxcbdrag.cpp
index 8ea0ebf966..10a827cfd9 100644
--- a/src/plugins/platforms/xcb/qxcbdrag.cpp
+++ b/src/plugins/platforms/xcb/qxcbdrag.cpp
@@ -309,7 +309,7 @@ xcb_window_t QXcbDrag::findRealWindow(const QPoint & pos, xcb_window_t w, int md
     return 0;
 }
 
-void QXcbDrag::move(const QPoint &globalPos)
+void QXcbDrag::move(const QPoint &globalPos, Qt::MouseButtons b, Qt::KeyboardModifiers mods)
 {
 
     if (source_sameanswer.contains(globalPos) && source_sameanswer.isValid())
@@ -470,15 +470,15 @@ void QXcbDrag::move(const QPoint &globalPos)
         source_time = connection()->time();
 
         if (w)
-            handle_xdnd_position(w, &move);
+            handle_xdnd_position(w, &move, b, mods);
         else
             xcb_send_event(xcb_connection(), false, proxy_target, XCB_EVENT_MASK_NO_EVENT, (const char *)&move);
     }
 }
 
-void QXcbDrag::drop(const QPoint &globalPos)
+void QXcbDrag::drop(const QPoint &globalPos, Qt::MouseButtons b, Qt::KeyboardModifiers mods)
 {
-    QBasicDrag::drop(globalPos);
+    QBasicDrag::drop(globalPos, b, mods);
 
     if (!current_target)
         return;
@@ -522,7 +522,7 @@ void QXcbDrag::drop(const QPoint &globalPos)
     }
 
     if (w) {
-        handleDrop(w, &drop);
+        handleDrop(w, &drop, b, mods);
     } else {
         xcb_send_event(xcb_connection(), false, current_proxy_target, XCB_EVENT_MASK_NO_EVENT, (const char *)&drop);
     }
@@ -710,7 +710,8 @@ void QXcbDrag::handleEnter(QPlatformWindow *window, const xcb_client_message_eve
         DEBUG() << "    " << connection()->atomName(xdnd_types.at(i));
 }
 
-void QXcbDrag::handle_xdnd_position(QPlatformWindow *w, const xcb_client_message_event_t *e)
+void QXcbDrag::handle_xdnd_position(QPlatformWindow *w, const xcb_client_message_event_t *e,
+                                    Qt::MouseButtons b, Qt::KeyboardModifiers mods)
 {
     QPoint p((e->data.data32[2] & 0xffff0000) >> 16, e->data.data32[2] & 0x0000ffff);
     Q_ASSERT(w);
@@ -743,7 +744,12 @@ void QXcbDrag::handle_xdnd_position(QPlatformWindow *w, const xcb_client_message
         supported_actions = Qt::DropActions(toDropAction(e->data.data32[4]));
     }
 
-    QPlatformDragQtResponse qt_response = QWindowSystemInterface::handleDrag(w->window(),dropData,p,supported_actions);
+    auto buttons = currentDrag() ? b : connection()->queryMouseButtons();
+    auto modifiers = currentDrag() ? mods : connection()->queryKeyboardModifiers();
+
+    QPlatformDragQtResponse qt_response = QWindowSystemInterface::handleDrag(
+                w->window(), dropData, p, supported_actions, buttons, modifiers);
+
     QRect answerRect(p + geometry.topLeft(), QSize(1,1));
     answerRect = qt_response.answerRect().translated(geometry.topLeft()).intersected(geometry);
 
@@ -887,7 +893,7 @@ void QXcbDrag::handleLeave(QPlatformWindow *w, const xcb_client_message_event_t
         DEBUG("xdnd drag leave from unexpected source (%x not %x", event->data.data32[0], xdnd_dragsource);
     }
 
-    QWindowSystemInterface::handleDrag(w->window(),0,QPoint(),Qt::IgnoreAction);
+    QWindowSystemInterface::handleDrag(w->window(), nullptr, QPoint(), Qt::IgnoreAction, 0, 0);
 
     xdnd_dragsource = 0;
     xdnd_types.clear();
@@ -899,7 +905,6 @@ void QXcbDrag::send_leave()
     if (!current_target)
         return;
 
-
     xcb_client_message_event_t leave;
     leave.response_type = XCB_CLIENT_MESSAGE;
     leave.sequence = 0;
@@ -933,7 +938,8 @@ void QXcbDrag::send_leave()
     waiting_for_status = false;
 }
 
-void QXcbDrag::handleDrop(QPlatformWindow *, const xcb_client_message_event_t *event)
+void QXcbDrag::handleDrop(QPlatformWindow *, const xcb_client_message_event_t *event,
+                          Qt::MouseButtons b, Qt::KeyboardModifiers mods)
 {
     DEBUG("xdndHandleDrop");
     if (!currentWindow) {
@@ -962,9 +968,6 @@ void QXcbDrag::handleDrop(QPlatformWindow *, const xcb_client_message_event_t *e
     } else {
         dropData = m_dropData;
         supported_drop_actions = accepted_drop_action;
-
-        // Drop coming from another app? Update keyboard modifiers.
-        QGuiApplicationPrivate::modifier_buttons = QGuiApplication::queryKeyboardModifiers();
     }
 
     if (!dropData)
@@ -975,7 +978,13 @@ void QXcbDrag::handleDrop(QPlatformWindow *, const xcb_client_message_event_t *e
     //            dropData = QDragManager::dragPrivate(X11->dndDropTransactions.at(at).object)->data;
     // if we can't find it, then use the data in the drag manager
 
-    QPlatformDropQtResponse response = QWindowSystemInterface::handleDrop(currentWindow.data(),dropData,currentPosition,supported_drop_actions);
+    auto buttons = currentDrag() ? b : connection()->queryMouseButtons();
+    auto modifiers = currentDrag() ? mods : connection()->queryKeyboardModifiers();
+
+    QPlatformDropQtResponse response = QWindowSystemInterface::handleDrop(
+                currentWindow.data(), dropData, currentPosition, supported_drop_actions,
+                buttons, modifiers);
+
     setExecutedDropAction(response.acceptedAction());
 
     xcb_client_message_event_t finished;