Windows QPA: Adjust margins for Windows App SDK compatibility

If using the ExtendsContentIntoTitleBar() method from the Windows App
SDK, the top margin becomes zero. The current approach does not account
for this, since it relies on the AdjustWindowRectExForDpi function.
Do a manual check after and correct if necessary, by comparing the
window and client sizes.

Fixes: QTBUG-113736
Change-Id: I62e0338b3ff7af47f5525dcccd0f9acfe9691819
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>
Reviewed-by: Wladimir Leuschner <wladimir.leuschner@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit 8dbc4824895ea9f87d1f6406fe2d22336b6253ed)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 3a54d31093ca8805e87d75f47c7bfab0cf595244)

1 files changed, 26 insertions, 3 deletions

diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 5105eab637..af1b95c336 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -1984,7 +1984,7 @@ void QWindowsWindow::handleDpiScaledSize(WPARAM wParam, LPARAM lParam, LRESULT *
     // add the margins for the new DPI to the window size.
     const UINT dpi = UINT(wParam);
     const qreal scale = dpiRelativeScale(dpi);
-    const QMargins margins = QWindowsGeometryHint::frame(window(), style(), exStyle(), dpi);
+    const QMargins margins = fullFrameMargins();
     if (!(m_data.flags & Qt::FramelessWindowHint)) {
         // We need to update the custom margins to match the current DPI, because
         // we don't want our users manually hook into this message just to set a
@@ -1994,7 +1994,7 @@ void QWindowsWindow::handleDpiScaledSize(WPARAM wParam, LPARAM lParam, LRESULT *
         m_data.customMargins *= scale;
     }
 
-    const QSize windowSize = (geometry().size() * scale).grownBy(margins + customMargins());
+    const QSize windowSize = (geometry().size() * scale).grownBy((margins * scale) + customMargins());
     SIZE *size = reinterpret_cast<SIZE *>(lParam);
     size->cx = windowSize.width();
     size->cy = windowSize.height();
@@ -2313,6 +2313,7 @@ void QWindowsWindow::handleGeometryChange()
 {
     const QRect previousGeometry = m_data.geometry;
     m_data.geometry = geometry_sys();
+    updateFullFrameMargins();
     QWindowSystemInterface::handleGeometryChange(window(), m_data.geometry);
     // QTBUG-32121: OpenGL/normal windows (with exception of ANGLE
     // which we no longer support in Qt 6) do not receive expose
@@ -2823,7 +2824,29 @@ void QWindowsWindow::calculateFullFrameMargins()
     const auto systemMargins = testFlag(DisableNonClientScaling)
         ? QWindowsGeometryHint::frameOnPrimaryScreen(window(), m_data.hwnd)
         : frameMargins_sys();
-    setFullFrameMargins(systemMargins + customMargins());
+
+    // QTBUG-113736: systemMargins depends on AdjustWindowRectExForDpi. This doesn't take into
+    // account possible external modifications to the titlebar, as with ExtendsContentIntoTitleBar()
+    // from the Windows App SDK. We can fix this by comparing the WindowRect (which includes the
+    // frame) to the ClientRect. If a 'typical' frame is detected, i.e. only the titlebar has been
+    // modified, we can safely adjust the frame by deducting the bottom margin to the total Y
+    // difference between the two rects, to get the actual size of the titlebar and prevent
+    // unwanted client area slicing.
+
+    RECT windowRect{};
+    RECT clientRect{};
+    GetWindowRect(handle(), &windowRect);
+    GetClientRect(handle(), &clientRect);
+    const int yDiff = (windowRect.bottom - windowRect.top) - clientRect.bottom;
+    const bool typicalFrame = (systemMargins.left() == systemMargins.right())
+            && (systemMargins.right() == systemMargins.bottom());
+
+    const QMargins adjustedMargins = typicalFrame ?
+          QMargins(systemMargins.left(), yDiff - systemMargins.bottom(),
+                   systemMargins.right(), systemMargins.bottom())
+            : systemMargins;
+
+    setFullFrameMargins(adjustedMargins + customMargins());
 }
 
 QMargins QWindowsWindow::frameMargins() const