Provide a fake approach to tablet event propagation

Summary:
At the moment, the state of wayland of getting such events isn't all
that clear. There's a zwp_tablet protocol that isn't stable yet and more
importantly isn't supported by Qt just yet.
Have it move and click the mouse about for now.

Depends on D25663 and D25763

Reviewers: #kwin, romangg

Reviewed By: #kwin, romangg

Subscribers: romangg, zzag, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D25764

input.cpp

@@ -1520,6 +1520,46 @@ public:
     }
 };
 
+/**
+ * Useful when there's no proper tablet support on the clients
+ */
+class FakeTabletInputFilter : public InputEventFilter
+{
+public:
+    FakeTabletInputFilter()
+    {
+    }
+
+    bool tabletToolEvent(QTabletEvent *event) override
+    {
+        if (!workspace()) {
+            return false;
+        }
+
+        switch (event->type()) {
+        case QEvent::TabletMove:
+        case QEvent::TabletEnterProximity:
+            input()->pointer()->processMotion(event->globalPosF(), event->timestamp());
+            break;
+        case QEvent::TabletPress:
+            input()->pointer()->processButton(KWin::qtMouseButtonToButton(Qt::LeftButton),
+                                              InputRedirection::PointerButtonPressed, event->timestamp());
+            break;
+        case QEvent::TabletRelease:
+            input()->pointer()->processButton(KWin::qtMouseButtonToButton(Qt::LeftButton),
+                                              InputRedirection::PointerButtonReleased, event->timestamp());
+            break;
+        case QEvent::TabletLeaveProximity:
+            break;
+        default:
+            qCWarning(KWIN_CORE) << "Unexpected tablet event type" << event;
+            break;
+        }
+        waylandServer()->simulateUserActivity();
+        return true;
+    }
+};
+
 class DragAndDropInputFilter : public InputEventFilter
 {
 public:
@@ -1881,6 +1921,7 @@ void InputRedirection::setupInputFilters()
     if (waylandServer()) {
         installInputEventFilter(new WindowActionInputFilter);
         installInputEventFilter(new ForwardInputFilter);
+        installInputEventFilter(new FakeTabletInputFilter);
     }
 }
 

pointer_input.cpp

@@ -81,6 +81,11 @@ static const QHash<uint32_t, Qt::MouseButton> s_buttonToQtMouseButton = {
     { 0x11f , Qt::ExtraButton13 },
 };
 
+uint32_t qtMouseButtonToButton(Qt::MouseButton button)
+{
+    return s_buttonToQtMouseButton.key(button);
+}
+
 static Qt::MouseButton buttonToQtMouseButton(uint32_t button)
 {
     // all other values get mapped to ExtraButton24
@@ -91,7 +96,6 @@ static Qt::MouseButton buttonToQtMouseButton(uint32_t button)
     // buttons are pressed is correct and that's all we care about.
     return s_buttonToQtMouseButton.value(button, Qt::ExtraButton24);
 }
-}
 
 static bool screenContainsPos(const QPointF &pos)
 {

pointer_input.h

@@ -57,6 +57,8 @@ namespace LibInput
 class Device;
 }
 
+uint32_t qtMouseButtonToButton(Qt::MouseButton button);
+
 class KWIN_EXPORT PointerInputRedirection : public InputDeviceHandler
 {
     Q_OBJECT