Disable event compression when the tablet events are accepted

Since Qt 4.5, all tablet events are compressed not to overload the
widgets with the corresponding mouse event (a mouse event is generated
if the tablet event is not accepted).

This behavior reduce the precision when drawing on a widget that use
the tablet events. All tablet events should be sent to the widget that
are accepting the tablet event.

With this patch, the tablet event are filtered only if the widget
ignore the first tablet event. The mouse events are compressed.

There is two special cases for the filtering:

First, if a tablet event is for another widget than the one
ignoring the tablet, this event should not be filtered.

Second, if there is a mouse press event, the mouse move event should be
sent to the widget that received the mouse press event.

Helped-by: Pierre Rossi
Reviewed-by: Thomas Zander
Reviewed-by: Bradley T. Hughes

1 files changed, 58 insertions, 53 deletions

diff --git a/src/gui/kernel/qapplication_x11.cpp b/src/gui/kernel/qapplication_x11.cpp
index 69dba40..0056b9e 100644
--- a/src/gui/kernel/qapplication_x11.cpp
+++ b/src/gui/kernel/qapplication_x11.cpp
@@ -4510,7 +4510,9 @@ void fetchWacomToolId(int &deviceType, qint64 &serialId)
 
 struct qt_tablet_motion_data
 {
-    Time timestamp;
+    bool filterByWidget;
+    const QWidget *widget;
+    const QWidget *etWidget;
     int tabletMotionType;
     bool error; // found a reason to stop searching
 };
@@ -4533,15 +4535,20 @@ static Bool qt_tabletMotion_scanner(Display *, XEvent *event, XPointer arg)
     qt_tablet_motion_data *data = (qt_tablet_motion_data *) arg;
     if (data->error)
         return false;
-
     if (event->type == data->tabletMotionType) {
-        if (data->timestamp > 0) {
-            if ((reinterpret_cast<const XDeviceMotionEvent*>(event))->time > data->timestamp) {
-                data->error = true;
-                return false;
+        const XDeviceMotionEvent *const motion = reinterpret_cast<const XDeviceMotionEvent*>(event);
+        if (data->filterByWidget) {
+            const QPoint curr(motion->x, motion->y);
+            const QWidget *w = data->etWidget;
+            const QWidget *const child = w->childAt(curr);
+            if (child) {
+                w = child;
             }
+            if (w == data->widget)
+                return true;
+        } else {
+            return true;
         }
-        return true;
     }
 
     data->error = event->type != MotionNotify; // we stop compression when another event gets in between.
@@ -4574,57 +4581,17 @@ bool QETWidget::translateXinputEvent(const XEvent *ev, QTabletDeviceData *tablet
     qreal rotation = 0;
     int deviceType = QTabletEvent::NoDevice;
     int pointerType = QTabletEvent::UnknownPointer;
-    XEvent mouseMotionEvent;
-    XEvent dummy;
     const XDeviceMotionEvent *motion = 0;
     XDeviceButtonEvent *button = 0;
     const XProximityNotifyEvent *proximity = 0;
     QEvent::Type t;
     Qt::KeyboardModifiers modifiers = 0;
-    bool reinsertMouseEvent = false;
-    XEvent mouseMotionEventSave;
 #if !defined (Q_OS_IRIX)
     XID device_id;
 #endif
 
     if (ev->type == tablet->xinput_motion) {
         motion = reinterpret_cast<const XDeviceMotionEvent*>(ev);
-
-        // Do event compression.  Skip over tablet+mouse move events if there are newer ones.
-        qt_tablet_motion_data tabletMotionData;
-        tabletMotionData.tabletMotionType = tablet->xinput_motion;
-        while (true) {
-            // Find first mouse event since we expect them in pairs inside Qt
-            tabletMotionData.error =false;
-            tabletMotionData.timestamp = 0;
-            if (XCheckIfEvent(X11->display, &mouseMotionEvent, &qt_mouseMotion_scanner, (XPointer) &tabletMotionData)) {
-                mouseMotionEventSave = mouseMotionEvent;
-                reinsertMouseEvent = true;
-            } else {
-                break;
-            }
-
-            // Now discard any duplicate tablet events.
-            tabletMotionData.error = false;
-            tabletMotionData.timestamp = mouseMotionEvent.xmotion.time;
-            while (XCheckIfEvent(X11->display, &dummy, &qt_tabletMotion_scanner, (XPointer) &tabletMotionData)) {
-                motion = reinterpret_cast<const XDeviceMotionEvent*>(&dummy);
-            }
-
-            // now check if there are more recent tablet motion events since we'll compress the current one with
-            // newer ones in that case
-            tabletMotionData.error = false;
-            tabletMotionData.timestamp = 0;
-            if (! XCheckIfEvent(X11->display, &dummy, &qt_tabletMotion_scanner, (XPointer) &tabletMotionData)) {
-                break; // done with compression
-            }
-            motion = reinterpret_cast<const XDeviceMotionEvent*>(&dummy);
-        }
-
-        if (reinsertMouseEvent) {
-            XPutBackEvent(X11->display, &mouseMotionEventSave);
-        }
-
         t = QEvent::TabletMove;
         global = QPoint(motion->x_root, motion->y_root);
         curr = QPoint(motion->x, motion->y);
@@ -4777,11 +4744,14 @@ bool QETWidget::translateXinputEvent(const XEvent *ev, QTabletDeviceData *tablet
     }
 #endif
 
-    QWidget *child = w->childAt(curr);
-    if (child) {
-        w = child;
-        curr = w->mapFromGlobal(global);
+    if (tablet->widgetToGetPress) {
+        w = tablet->widgetToGetPress;
+    } else {
+        QWidget *child = w->childAt(curr);
+        if (child)
+            w = child;
     }
+    curr = w->mapFromGlobal(global);
 
     if (t == QEvent::TabletPress) {
         tablet->widgetToGetPress = w;
@@ -4795,10 +4765,45 @@ bool QETWidget::translateXinputEvent(const XEvent *ev, QTabletDeviceData *tablet
                    deviceType, pointerType,
                    qreal(pressure / qreal(tablet->maxPressure - tablet->minPressure)),
                    xTilt, yTilt, tangentialPressure, rotation, z, modifiers, uid);
-    if (proximity)
+    if (proximity) {
         QApplication::sendSpontaneousEvent(qApp, &e);
-    else
+    } else {
         QApplication::sendSpontaneousEvent(w, &e);
+        const bool accepted = e.isAccepted();
+        if (!accepted && ev->type == tablet->xinput_motion) {
+            // If the widget does not accept tablet events, we drop the next ones from the event queue
+            // for this widget so it is not overloaded with the numerous tablet events.
+            qt_tablet_motion_data tabletMotionData;
+            tabletMotionData.tabletMotionType = tablet->xinput_motion;
+            tabletMotionData.widget = w;
+            tabletMotionData.etWidget = this;
+            // if nothing is pressed, the events are filtered by position
+            tabletMotionData.filterByWidget = (tablet->widgetToGetPress == 0);
+
+            bool reinsertMouseEvent = false;
+            XEvent mouseMotionEvent;
+            while (true) {
+                // Find first mouse event since we expect them in pairs inside Qt
+                tabletMotionData.error =false;
+                if (XCheckIfEvent(X11->display, &mouseMotionEvent, &qt_mouseMotion_scanner, (XPointer) &tabletMotionData)) {
+                    reinsertMouseEvent = true;
+                } else {
+                    break;
+                }
+
+                // Now discard any duplicate tablet events.
+                tabletMotionData.error = false;
+                XEvent dummy;
+                while (XCheckIfEvent(X11->display, &dummy, &qt_tabletMotion_scanner, (XPointer) &tabletMotionData)) {
+                    // just discard the event
+                }
+            }
+
+            if (reinsertMouseEvent) {
+                XPutBackEvent(X11->display, &mouseMotionEvent);
+            }
+        }
+    }
     return true;
 }
 #endif