Resize the window when the screen's dpi changes

That's what the MSDN documentation say one should do in the handler
for WM_DPICHANGED

[ChangeLog][QtGui][Windows] Windows are now automatically resized
when they are moved on a screen to adapt to the new pixel ratio.

Task-number: QTBUG-55510
Task-number: QTBUG-48242
Change-Id: I7688f12165f76585d75686e2e94b0fc562627be2
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index fefc848d01..5745fc6d19 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -1088,6 +1088,15 @@ bool QWindowsContext::windowsProc(HWND hwnd, UINT message,
         return true;
 #endif
     }   break;
+    case QtWindows::DpiChangedEvent: {
+        platformWindow->setFlag(QWindowsWindow::WithinDpiChanged);
+        const RECT *prcNewWindow = reinterpret_cast<RECT *>(lParam);
+        SetWindowPos(hwnd, NULL, prcNewWindow->left, prcNewWindow->top,
+                     prcNewWindow->right - prcNewWindow->left,
+                     prcNewWindow->bottom - prcNewWindow->top, SWP_NOZORDER | SWP_NOACTIVATE);
+        platformWindow->clearFlag(QWindowsWindow::WithinDpiChanged);
+        return true;
+    }
 #if !defined(QT_NO_SESSIONMANAGER)
     case QtWindows::QueryEndSessionApplicationEvent: {
         QWindowsSessionManager *sessionManager = platformSessionManager();