I have found out that this problem is mainly related to WinAPI + framelessness, not to Qt. I didn't manage to find any working WinAPI solution, for example, I've tried this one: melak47's solution. So I've chosen Qt way. This approach is not as concise as I expected from the WinAPI approach, but it works.
Here is a code snippet describing only the necessary parts.
.hpp
class FramelessWindow : public QQuickWindow { Q_OBJECT QML_ELEMENT Q_PROPERTY(bool isMaximized READ isMaximized NOTIFY isMaximizedChanged) signals: void isMaximizedChanged(); public: FramelessWindow() noexcept; Q_INVOKABLE void showNormal() noexcept; Q_INVOKABLE void showMaximized() noexcept; bool isMaximized() const noexcept; private: bool eventFilter(QObject* watched, QEvent* event) override; bool nativeEvent(const QByteArray& eventType, void* message, qintptr* result) override; QRect restoredGeometry_; bool isMaximized_; };.cpp
FramelessWindow::FramelessWindow() noexcept : isMaximized_ { false } { setFlags(Qt::Window | Qt::FramelessWindowHint | Qt::WindowSystemMenuHint | Qt::WindowMaximizeButtonHint); installEventFilter(this); SetWindowLongPtr((HWND)winId(), GWL_STYLE, WS_POPUP | WS_THICKFRAME | WS_CAPTION | WS_SYSMENU | WS_MAXIMIZEBOX | WS_MINIMIZEBOX); } void FramelessWindow::showNormal() noexcept { setGeometry(restoredGeometry_); isMaximized_ = false; emit isMaximizedChanged(); } void FramelessWindow::showMaximized() noexcept { restoredGeometry_ = geometry(); setGeometry(screen()->availableGeometry()); isMaximized_ = true; emit isMaximizedChanged(); } bool FramelessWindow::isMaximized() const noexcept { return isMaximized_; } bool FramelessWindow::eventFilter(QObject* watched, QEvent* event) { QPoint cursorPos = QCursor::pos(); qreal dpr = devicePixelRatio(); QRect draggingArea = geometry(); draggingArea.setHeight(32 * dpr); draggingArea.setY(draggingArea.y() + dpr * ResizeBorderWidth); if (draggingArea.contains(cursorPos)) { if (event->type() == QEvent::MouseButtonPress) { if (isMaximized_) { restoredGeometry_.moveTo({ QCursor::pos().x() - restoredGeometry_.width() / 2, QCursor::pos().y() - 10 }); showNormal(); } startSystemMove(); return true; } else if (isResizable_ && event->type() == QEvent::MouseButtonDblClick) { if (draggingArea.contains(cursorPos)) { if (isMaximized_) { showNormal(); } else { showMaximized(); } return true; } } else if (event->type() == QEvent::WindowStateChange && QWindow::visibility() == QWindow::Maximized) { setGeometry(screen()->availableGeometry()); isMaximized_ = true; emit isMaximizedChanged(); return true; } } return QQuickWindow::eventFilter(watched, event); } bool FramelessWindow::nativeEvent(const QByteArray& eventType, void* message, qintptr* result) { if (auto* msg = static_cast<MSG*>(message); msg->message == WM_NCCALCSIZE) { NCCALCSIZE_PARAMS& params = *reinterpret_cast<NCCALCSIZE_PARAMS*>(msg->lParam); if (params.rgrc[0].top != 0) { --params.rgrc[0].top; } *result = 0; return true; } return QQuickWindow::nativeEvent(eventType, message, result); }
