Windows QPA: Fix detection of the Surface Pen eraser button

The Surface Pen eraser button generates Meta+F18/19/20 keystrokes, but
when it is not touching the screen the Fn WM_KEYDOWN message is eaten
and only a Fn WM_KEYUP message with the previous state as "not pressed"
is generated, which would be ignored. With this patch we detect this
case and synthesize the expected key events to allow the button to be
used in applications.

Fixes: QTBUG-77153
Change-Id: I075f5cbb903cb36c9ec241ee1bb31d436b725e3a
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

1 files changed, 17 insertions, 1 deletions

diff --git a/src/plugins/platforms/windows/qwindowskeymapper.cpp b/src/plugins/platforms/windows/qwindowskeymapper.cpp
index c5af4d8042..da630005d6 100644
--- a/src/plugins/platforms/windows/qwindowskeymapper.cpp
+++ b/src/plugins/platforms/windows/qwindowskeymapper.cpp
@@ -1301,7 +1301,23 @@ bool QWindowsKeyMapper::translateKeyEventInternal(QWindow *window, MSG msg,
                       || code == Qt::Key_Control
                       || code == Qt::Key_Meta
                       || code == Qt::Key_Alt)) {
-            // Someone ate the key down event
+
+            // Workaround for QTBUG-77153:
+            // The Surface Pen eraser button generates Meta+F18/19/20 keystrokes,
+            // but when it is not touching the screen the Fn Down is eaten and only
+            // a Fn Up with the previous state as "not pressed" is generated, which
+            // would be ignored. We detect this case and synthesize the expected events.
+            if ((msg.lParam & 0x40000000) == 0 &&
+                    Qt::KeyboardModifier(state) == Qt::NoModifier &&
+                    ((code == Qt::Key_F18) || (code == Qt::Key_F19) || (code == Qt::Key_F20))) {
+                QWindowSystemInterface::handleExtendedKeyEvent(receiver, QEvent::KeyPress, code,
+                                                               Qt::MetaModifier, scancode,
+                                                               quint32(msg.wParam), MetaLeft);
+                QWindowSystemInterface::handleExtendedKeyEvent(receiver, QEvent::KeyRelease, code,
+                                                               Qt::NoModifier, scancode,
+                                                               quint32(msg.wParam), 0);
+                result = true;
+            }
         } else {
             if (!code)
                 code = asciiToKeycode(rec->ascii ? char(rec->ascii) : char(msg.wParam), state);