Windows: Register windows for touch when a device is plugged in

Call QWindowsWindow::registerTouchWindow() for all windows when a device
is plugged in while the application is running. Guard
registerTouchWindow() against repetitive invocation and wrong window
types. This amends the crash fix 7daae2c2c706fd5d1c1ae44ace6847bc297803a0
and touch should then work.

Task-number: QTBUG-48849
Change-Id: I8b257dda144f28d60bcc5c4e369a413a90263998
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

3 files changed, 20 insertions, 1 deletions

diff --git a/src/plugins/platforms/windows/qtwindowsglobal.h b/src/plugins/platforms/windows/qtwindowsglobal.h
index a5c05bf1a3..e703b5d47e 100644
--- a/src/plugins/platforms/windows/qtwindowsglobal.h
+++ b/src/plugins/platforms/windows/qtwindowsglobal.h
@@ -120,6 +120,7 @@ enum WindowsEventType // Simplify event types
     QueryEndSessionApplicationEvent = ApplicationEventFlag + 4,
     EndSessionApplicationEvent = ApplicationEventFlag + 5,
     AppCommandEvent = ApplicationEventFlag + 6,
+    DeviceChangeEvent = ApplicationEventFlag + 7,
     InputMethodStartCompositionEvent = InputMethodEventFlag + 1,
     InputMethodCompositionEvent = InputMethodEventFlag + 2,
     InputMethodEndCompositionEvent = InputMethodEventFlag + 3,
@@ -271,6 +272,8 @@ inline QtWindows::WindowsEventType windowsEventType(UINT message, WPARAM wParamI
 #endif
     case WM_GESTURE:
         return QtWindows::GestureEvent;
+    case WM_DEVICECHANGE:
+        return QtWindows::DeviceChangeEvent;
     case WM_DPICHANGED:
         return QtWindows::DpiChangedEvent;
     default:
diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index 5745fc6d19..b7a866679f 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -79,6 +79,7 @@
 #include <stdio.h>
 #include <windowsx.h>
 #include <comdef.h>
+#include <dbt.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -322,6 +323,13 @@ bool QWindowsContext::initTouch(unsigned integrationOptions)
     QWindowSystemInterface::registerTouchDevice(touchDevice);
 
     d->m_systemInfo |= QWindowsContext::SI_SupportsTouch;
+
+    // A touch device was plugged while the app is running. Register all windows for touch.
+    if (QGuiApplicationPrivate::is_app_running) {
+        for (QWindowsWindow *w : qAsConst(d->m_windows))
+            w->registerTouchWindow();
+    }
+
     return true;
 }
 
@@ -965,6 +973,13 @@ bool QWindowsContext::windowsProc(HWND hwnd, UINT message,
     }
 
     switch (et) {
+    case QtWindows::DeviceChangeEvent:
+        if (d->m_systemInfo & QWindowsContext::SI_SupportsTouch)
+            break;
+        // See if there are any touch devices added
+        if (wParam == DBT_DEVNODES_CHANGED)
+            initTouch();
+        break;
     case QtWindows::KeyboardLayoutChangeEvent:
         if (QWindowsInputContext *wic = windowsInputContext())
             wic->handleInputLanguageChanged(wParam, lParam);
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 79dce2fc43..2875463e62 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -2411,7 +2411,8 @@ void QWindowsWindow::setTouchWindowTouchTypeStatic(QWindow *window, QWindowsWind
 
 void QWindowsWindow::registerTouchWindow(QWindowsWindowFunctions::TouchWindowTouchTypes touchTypes)
 {
-    if ((QWindowsContext::instance()->systemInfo() & QWindowsContext::SI_SupportsTouch)) {
+    if ((QWindowsContext::instance()->systemInfo() & QWindowsContext::SI_SupportsTouch)
+        && !testFlag(TouchRegistered)) {
         ULONG touchFlags = 0;
         const bool ret = QWindowsContext::user32dll.isTouchWindow(m_data.hwnd, &touchFlags);
         // Return if it is not a touch window or the flags are already set by a hook