From 7955f5b084aeae334a445136839160356c96de36 Mon Sep 17 00:00:00 2001
From: Sine Striker <trueful@163.com>
Date: 周三, 20 12月 2023 03:59:57 +0800
Subject: [PATCH] Add comments
---
src/core/contexts/win32windowcontext.cpp | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++--
1 files changed, 50 insertions(+), 2 deletions(-)
diff --git a/src/core/contexts/win32windowcontext.cpp b/src/core/contexts/win32windowcontext.cpp
index cd1ab62..145b19c 100644
--- a/src/core/contexts/win32windowcontext.cpp
+++ b/src/core/contexts/win32windowcontext.cpp
@@ -911,7 +911,7 @@
}
}
- break;
+ return;
}
case DefaultColorsHook: {
@@ -965,7 +965,6 @@
}
default: {
- // unreachable
break;
}
}
@@ -1268,6 +1267,53 @@
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 area message, and it
+ // will be ignored by Qt. As a consequence, QWidgetWindow can't receive a
+ // mouse release messages 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 +1376,8 @@
// 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);
}
}
--
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