Cocoa: deal with unexpected tablet events without proximity

If the user has a Wacom stylus in proximity of the tablet already
(perhaps left it lying on the tablet) and starts a Qt application, we
don't get to see a proximity enter event, so a lot of device information
is missing; nevertheless, creating a stop-gap device (with ID 0, type
Unknown) makes it possible to get basic QTabletEvents with pressure,
until the next time the stylus leaves and comes back into proximity.

Pick-to: 6.4
Fixes: QTBUG-65559
Change-Id: Ibacbdb78461c0b62d4040c80d210a1b06074e952
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 10 insertions, 6 deletions

diff --git a/src/plugins/platforms/cocoa/qnsview_tablet.mm b/src/plugins/platforms/cocoa/qnsview_tablet.mm
index 72e1b2d78f..4c6e351b3f 100644
--- a/src/plugins/platforms/cocoa/qnsview_tablet.mm
+++ b/src/plugins/platforms/cocoa/qnsview_tablet.mm
@@ -34,14 +34,18 @@ Q_GLOBAL_STATIC(QCocoaTabletDeviceMap, devicesInProximity)
 
     // We use devicesInProximity because deviceID is typically 0,
     // so QInputDevicePrivate::fromId() won't work.
-    const auto *device = devicesInProximity->value(theEvent.deviceID);
-    if (!device) {
-        // Error: Unknown tablet device. Qt also gets into this state
-        // when running on a VM. This appears to be harmless; don't
-        // print a warning.
-        return false;
+    const auto deviceId = theEvent.deviceID;
+    const auto *device = devicesInProximity->value(deviceId);
+    if (!device && deviceId == 0) {
+        // Application started up with stylus in proximity already, so we missed the proximity event?
+        // Create a generic tablet device for now.
+        device = tabletToolInstance(theEvent);
+        devicesInProximity->insert(deviceId, device);
     }
 
+    if (Q_UNLIKELY(!device))
+        return false;
+
     bool down = (eventType != NSEventTypeMouseMoved);
 
     qreal pressure;