From 3871bfc5d3aff45e498fa2944c27e6eb5d146c8e Mon Sep 17 00:00:00 2001
From: SineStriker <trueful@163.com>
Date: 周三, 20 12月 2023 19:56:32 +0800
Subject: [PATCH] Add mac hot-switch implementations

---
 src/core/contexts/win32windowcontext.cpp |   82 ++++++++++++++++++++++++++++++++++++----
 1 files changed, 73 insertions(+), 9 deletions(-)

diff --git a/src/core/contexts/win32windowcontext.cpp b/src/core/contexts/win32windowcontext.cpp
index cd1ab62..40fda7c 100644
--- a/src/core/contexts/win32windowcontext.cpp
+++ b/src/core/contexts/win32windowcontext.cpp
@@ -117,7 +117,7 @@
     private:
         DynamicApis() {
 #define DYNAMIC_API_RESOLVE(DLL, NAME)                                                             \
-    p##NAME = reinterpret_cast<decltype(p##NAME)>(DLL.resolve(#NAME))
+  p##NAME = reinterpret_cast<decltype(p##NAME)>(DLL.resolve(#NAME))
 
             QSystemLibrary user32(QStringLiteral("user32"));
             DYNAMIC_API_RESOLVE(user32, GetDpiForWindow);
@@ -845,6 +845,7 @@
         g_wndProcHash->insert(hWnd, ctx);
     }
 
+    template <bool Destroyed = true>
     static inline void removeManagedWindow(HWND hWnd) {
         // Remove window handle mapping
         if (!g_wndProcHash->remove(hWnd))
@@ -853,6 +854,11 @@
         // Remove event filter if the all windows has been destroyed
         if (g_wndProcHash->empty()) {
             WindowsNativeEventFilter::uninstall();
+        }
+
+        // Restore window proc
+        if constexpr (!Destroyed) {
+            ::SetWindowLongPtrW(hWnd, GWLP_WNDPROC, reinterpret_cast<LONG_PTR>(g_qtWindowProc));
         }
     }
 
@@ -911,7 +917,7 @@
                     }
                 }
 
-                break;
+                return;
             }
 
             case DefaultColorsHook: {
@@ -964,10 +970,8 @@
                 return;
             }
 
-            default: {
-                // unreachable
+            default:
                 break;
-            }
         }
         AbstractWindowContext::virtual_hook(id, data);
     }
@@ -980,8 +984,19 @@
         return getWindowFrameBorderThickness(reinterpret_cast<HWND>(windowId));
     }
 
-    void Win32WindowContext::winIdChanged(QWindow *oldWindow) {
-        removeManagedWindow(reinterpret_cast<HWND>(windowId));
+    void Win32WindowContext::winIdChanged(QWindow *oldWindow, bool isDestroyed) {
+        Q_UNUSED(isDestroyed)
+
+        // If the original window id is valid, remove all resources related
+        if (windowId) {
+            if (isDestroyed) {
+                removeManagedWindow(reinterpret_cast<HWND>(windowId));
+            } else {
+                removeManagedWindow<false>(reinterpret_cast<HWND>(windowId));
+            }
+            windowId = 0;
+        }
+
         if (!m_windowHandle) {
             return;
         }
@@ -1001,7 +1016,7 @@
 #endif
 
         // Inform Qt we want and have set custom margins
-        updateInternalWindowFrameMargins(hWnd, m_windowHandle);
+        updateInternalWindowFrameMargins(hWnd, m_windowHandle); // TODO: Restore?
 
         // Add managed window
         addManagedWindow(hWnd, this);
@@ -1268,6 +1283,53 @@
                 const WindowPart currentWindowPart = lastHitTestResult;
                 if (message == WM_NCMOUSEMOVE) {
                     if (currentWindowPart != WindowPart::ChromeButton) {
+                        // https://github.com/qt/qtbase/blob/e26a87f1ecc40bc8c6aa5b889fce67410a57a702/src/widgets/kernel/qwidgetwindow.cpp#L472
+                        // When the mouse press event arrives, QWidgetWindow will implicitly grab
+                        // the top widget right under the mouse, and set `qt_button_down` to this
+                        // widget. At this time, no other widgets will accept the mouse event until
+                        // QWidgetWindow receives the mouse release event, then set `qt_button_down`
+                        // to null.
+
+                        // Imagine the following situation, now the main window has a pop-up menu,
+                        // the focus is not on the main window, if we click outside the pop-up menu,
+                        // the menu will close, which seems to be completely fine. But if we close
+                        // the menu by clicking on the title bar draggable area, then other widgets
+                        // won't accept the mouse message afterwards.
+
+                        // Here's the reason.
+                        // When the mouse is placed in the draggable area of the title bar, there
+                        // are two situations.
+
+                        // 1. If the focus is on the main window, and the last result of
+                        // WM_NCHITTEST is HTCAPTION, the mouse click event in the title bar is
+                        // taken over by Windows and Qt does not receive the mouse click event.
+
+                        // 2. If the main window has a pop-up menu, it is completely different. When
+                        // the mouse is pressed on the title bar, Windows sends the WM_LBUTTONDOWN
+                        // message to the window plane of the pop-up menu, the menu is closed, but
+                        // Qt will continue to forward the event to the QWidget under the mouse, and
+                        // the event will be processed by QWidgetWindow, causing the title bar
+                        // widget to be implicitly grabbed. After the menu is closed, Windows
+                        // immediately sends WM_NCHITTEST, because the mouse is in the title bar
+                        // draggable area, the result is HTCAPTION, so when the mouse is released,
+                        // Windows sends WM_NCLBUTTONUP, which is a non-client message, and it
+                        // will be ignored by Qt. As a consequence, QWidgetWindow can't receive a
+                        // mouse release message in the client area, so the grab remains, and other
+                        // widgets cannot receive mouse events.
+
+                        // Since we didn't watch the menu window, we cannot capture any mouse
+                        // press events sent by Windows, so we cannot solve this problem by
+                        // recording mouse events. Fortunately, we found that the main window will
+                        // receive a WM_NCMOUSEMOVE message immediately after the menu is closed, so
+                        // we just manually send a mouse release event when this message arrives and
+                        // set qt_button_down to null. Don't worry, when receiving WM_NCMOUSEMOVE,
+                        // there shouldn't be any control in the state of being grabbed.
+
+                        // In the native window, although QWidgetWindow handles the forwarded mouse
+                        // press event when the menu is closed, since the native title bar is not a
+                        // QWidget, no widget will be grabbed, and `qt_button_down` remains empty,
+                        // the above problems would not arise.
+
                         m_delegate->resetQtGrabbedControl(m_host);
                         if (mouseLeaveBlocked) {
                             emulateClientAreaMessage(hWnd, message, wParam, lParam,
@@ -1330,6 +1392,8 @@
                         // window from client area, which means we will get previous window part as
                         // HTCLIENT if the mouse leaves window from client area and enters window
                         // from non-client area, but it has no bad effect.
+
+                        // Why do we need to call this function here?
                         m_delegate->resetQtGrabbedControl(m_host);
                     }
                 }
@@ -1561,7 +1625,7 @@
                         *result = (isTitleBar ? HTCAPTION : HTCLIENT);
                         return true;
                     }
-                    // At this point, we know that the cursor is inside the client area
+                    // At this point, we know that the cursor is inside the client area,
                     // so it has to be either the little border at the top of our custom
                     // title bar or the drag bar. Apparently, it must be the drag bar or
                     // the little border at the top which the user can use to move or

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