Fix native child widget (#133)

* Fix WM_NCCALCSIZE handler

* Add comment

Author: SineStriker

README.md

@@ -276,17 +276,14 @@ See [examples](examples) for more demo use cases. The examples have no High DPI
 - Once you have made the window frameless, it will not be able to switch back to the system frame again unless you destroy your window and recreate it with different settings.
 
 #### Native Child Widget
-- There **must not** be any internal child widget with `Qt::WA_NativeWindow` property enabled, otherwise the native features and display may be abnormal. Therefore, do not set any widget that has called `QWidget::winId()` or `QWidget::setAttribute(Qt::WA_NativeWindow)` as a descendant of a frameless window.
-    - If you really need to move widgets between different windows, make sure that the widget is not a top-level window and wrap it with a frameless container window.
+- If you are about to add a widget with `Qt::WA_NativeWindow` property enabled as a descendent of the frameless window, you should enable `Qt::WA_DontCreateNativeAncestors` of it in advance.
 
 #### Size Constrains
 - If you want to disable window resizing, you can set a fixed size, which is officially supported by QWindowKit. If you use other special means to achieve this, QWK doesn't guarantee everything can still be fully functional.
 - If you set a maximized width or height, the window should not be maximized because you cannot get the correct window size through Qt APIs. You may workaround this by using system APIs such as `GetWindowRect` or `GetClientRect`. The root cause lies deep in Qt QPA implementations and currently we don't know how to fix it without modifying Qt itself.
 
 #### Windows 10
-
 - Due to the inherent defects in the Windows 10 window system, the top border will disappear when the system title bar is removed. We have filtered Qt's event and perfectly reshown the system top border, thanks to the implementation of Windows Terminal for our reference. However, this workaround only works with QtWidgets and QtQuick (**only when rendering through D3D**) applications.
-
 - In QtQuick applications that use OpenGL or other rendering backends, we use Qt's painting system to emulate this border. But since Windows 10 system border is translucent, the difference from the system border is more noticeable in a dark background.
 
 ## TODO

src/core/contexts/win32windowcontext.cpp

@@ -834,9 +834,7 @@ namespace QWK {
         }
 
         if (key == QStringLiteral("title-bar-height")) {
-            return m_windowId
-                       ? int(getTitleBarHeight(reinterpret_cast<HWND>(m_windowId)))
-                       : 0;
+            return m_windowId ? int(getTitleBarHeight(reinterpret_cast<HWND>(m_windowId))) : 0;
         }
         return AbstractWindowContext::windowAttribute(key);
     }
@@ -1695,7 +1693,8 @@ namespace QWK {
                         // outside the window, that is, the three transparent window resize area.
                         // Returning HTCLIENT will confuse Windows, we can't put our controls there
                         // anyway.
-                        *result = HTNOWHERE; // Make sure we can know we don't set any value explicitly later.
+                        *result = HTNOWHERE; // Make sure we can know we don't set any value
+                                             // explicitly later.
                         if (originalHitTestResult == HTCAPTION) {
                         } else if (isFixedSize || dontOverrideCursor) {
                             *result = HTBORDER;
@@ -1724,11 +1723,13 @@ namespace QWK {
                                 } else {
                                     *result = HTLEFT;
                                 }
-                            } else if (originalHitTestResult == HTLEFT || originalHitTestResult == HTRIGHT) {
+                            } else if (originalHitTestResult == HTLEFT ||
+                                       originalHitTestResult == HTRIGHT) {
                                 if (isFixedWidth) {
                                     *result = HTBORDER;
                                 }
-                            } else if (originalHitTestResult == HTTOP || originalHitTestResult == HTBOTTOM) {
+                            } else if (originalHitTestResult == HTTOP ||
+                                       originalHitTestResult == HTBOTTOM) {
                                 if (isFixedHeight) {
                                     *result = HTBORDER;
                                 }
@@ -1757,7 +1758,8 @@ namespace QWK {
                         // inside our homemade title bar now, return HTCLIENT to let our
                         // title bar can still capture mouse events.
                         *result = [&]() {
-                            if (isFixedSize || isFixedHeight || dontOverrideCursor || (isFixedWidth && (isInLeftBorder || isInRightBorder))) {
+                            if (isFixedSize || isFixedHeight || dontOverrideCursor ||
+                                (isFixedWidth && (isInLeftBorder || isInRightBorder))) {
                                 if (isInTitleBar) {
                                     return HTCAPTION;
                                 } else {
@@ -2173,7 +2175,10 @@ namespace QWK {
         // of the upper-left non-client area. It's confirmed that this issue exists
         // from Windows 7 to Windows 10. Not tested on Windows 11 yet. Don't know
         // whether it exists on Windows XP to Windows Vista or not.
-        *result = wParam ? WVR_REDRAW : FALSE;
+
+        // https://github.com/chromium/chromium/blob/5d297da3cf2a642e9ace2b23fed097370bc70814/ui/views/win/hwnd_message_handler.cc#L2330
+        // Do not return WVR_REDRAW otherwise child HWNDs will be mispositioned.
+        *result = FALSE;
         return true;
     }