1 files changed, 21 insertions, 12 deletions

diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index 6c1f5c8f93..281f18af5b 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -210,6 +210,7 @@ void QWindowsUser32DLL::init()
 
     if (QOperatingSystemVersion::current()
         >= QOperatingSystemVersion(QOperatingSystemVersion::Windows, 10, 0, 14393)) {
+        adjustWindowRectExForDpi = (AdjustWindowRectExForDpi)library.resolve("AdjustWindowRectExForDpi");
         enableNonClientDpiScaling = (EnableNonClientDpiScaling)library.resolve("EnableNonClientDpiScaling");
         getWindowDpiAwarenessContext = (GetWindowDpiAwarenessContext)library.resolve("GetWindowDpiAwarenessContext");
         getAwarenessFromDpiAwarenessContext = (GetAwarenessFromDpiAwarenessContext)library.resolve("GetAwarenessFromDpiAwarenessContext");
@@ -977,7 +978,7 @@ static inline bool resizeOnDpiChanged(const QWindow *w)
     return result;
 }
 
-static bool shouldHaveNonClientDpiScaling(const QWindow *window)
+bool QWindowsContext::shouldHaveNonClientDpiScaling(const QWindow *window)
 {
     return QOperatingSystemVersion::current() >= QOperatingSystemVersion::Windows10
         && window->isTopLevel()
@@ -1321,17 +1322,24 @@ bool QWindowsContext::windowsProc(HWND hwnd, UINT message,
 #endif
     }   break;
     case QtWindows::DpiChangedEvent: {
-        if (!resizeOnDpiChanged(platformWindow->window()))
-            return false;
-        platformWindow->setFlag(QWindowsWindow::WithinDpiChanged);
-        const RECT *prcNewWindow = reinterpret_cast<RECT *>(lParam);
-        qCDebug(lcQpaWindows) << __FUNCTION__ << "WM_DPICHANGED"
-            << platformWindow->window() << *prcNewWindow;
-        SetWindowPos(hwnd, nullptr, prcNewWindow->left, prcNewWindow->top,
-                     prcNewWindow->right - prcNewWindow->left,
-                     prcNewWindow->bottom - prcNewWindow->top, SWP_NOZORDER | SWP_NOACTIVATE);
-        platformWindow->clearFlag(QWindowsWindow::WithinDpiChanged);
-        return true;
+        // Try to apply the suggested size first and then notify ScreenChanged
+        // so that the resize event sent from QGuiApplication incorporates it
+        // WM_DPICHANGED is sent with a size that avoids resize loops (by
+        // snapping back to the previous screen, see QTBUG-65580).
+        const bool doResize = resizeOnDpiChanged(platformWindow->window());
+        if (doResize) {
+            platformWindow->setFlag(QWindowsWindow::WithinDpiChanged);
+            platformWindow->updateFullFrameMargins();
+            const auto prcNewWindow = reinterpret_cast<RECT *>(lParam);
+            qCDebug(lcQpaWindows) << __FUNCTION__ << "WM_DPICHANGED"
+                << platformWindow->window() << *prcNewWindow;
+            SetWindowPos(hwnd, nullptr, prcNewWindow->left, prcNewWindow->top,
+                         prcNewWindow->right - prcNewWindow->left,
+                         prcNewWindow->bottom - prcNewWindow->top, SWP_NOZORDER | SWP_NOACTIVATE);
+            platformWindow->clearFlag(QWindowsWindow::WithinDpiChanged);
+        }
+        platformWindow->checkForScreenChanged(QWindowsWindow::FromDpiChange);
+        return doResize;
     }
 #if QT_CONFIG(sessionmanager)
     case QtWindows::QueryEndSessionApplicationEvent: {
@@ -1589,6 +1597,7 @@ extern "C" LRESULT QT_WIN_CALLBACK qWindowsWndProc(HWND hwnd, UINT message, WPAR
             marginsFromRects(ncCalcSizeFrame, rectFromNcCalcSize(message, wParam, lParam, 0));
         if (margins.left() >= 0) {
             if (platformWindow) {
+                qCDebug(lcQpaWindows) << __FUNCTION__ << "WM_NCCALCSIZE for" << hwnd << margins;
                 platformWindow->setFullFrameMargins(margins);
             } else {
                 const QSharedPointer<QWindowCreationContext> ctx = QWindowsContext::instance()->windowCreationContext();