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QWindowKit Tutorial

Language: English | 简体中文

Project README: English | 简体中文

This tutorial shows how to use QWindowKit in Qt Widgets and Qt Quick applications to build a custom title bar while keeping native behaviors such as moving, resizing, system menus, and Windows Snap Layout.

QWindowKit provides three modules:

  • QWindowKit::Core: shared platform window infrastructure.
  • QWindowKit::Widgets: integration for QWidget and QMainWindow.
  • QWindowKit::Quick: integration for QQuickWindow and QML Window.

Requirements

  • Qt 5.12 or later. For real applications, Qt 5.15.2+ or Qt 6.6.2+ is recommended.
  • A C++17 compiler.
  • CMake 3.19 or later.
  • Windows, macOS, or Linux.

Build And Install

Build from source:

git clone --recursive https://github.com/stdware/qwindowkit
cd qwindowkit

cmake -S . -B build ^
  -DCMAKE_PREFIX_PATH=C:/Qt/6.7.3/msvc2019_64 ^
  -DCMAKE_INSTALL_PREFIX=C:/Libraries/QWindowKit ^
  -DQWINDOWKIT_BUILD_WIDGETS=ON ^
  -DQWINDOWKIT_BUILD_QUICK=ON ^
  -DQWINDOWKIT_BUILD_EXAMPLES=OFF

cmake --build build --config Release
cmake --install build --config Release

On Linux or macOS:

cmake -S . -B build \
  -DCMAKE_PREFIX_PATH=/path/to/Qt \
  -DCMAKE_INSTALL_PREFIX=/opt/qwindowkit \
  -DQWINDOWKIT_BUILD_WIDGETS=ON \
  -DQWINDOWKIT_BUILD_QUICK=ON

cmake --build build --config Release
cmake --install build --config Release

Common options:

-DQWINDOWKIT_BUILD_WIDGETS=ON
-DQWINDOWKIT_BUILD_QUICK=ON
-DQWINDOWKIT_BUILD_EXAMPLES=ON
-DQWINDOWKIT_BUILD_STATIC=OFF
-DQWINDOWKIT_FORCE_QT_WINDOW_CONTEXT=OFF
-DQWINDOWKIT_ENABLE_WINDOWS_SYSTEM_BORDERS=ON

Use From CMake

Widgets application:

cmake_minimum_required(VERSION 3.19)
project(MyWidgetsApp LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 REQUIRED COMPONENTS Core Gui Widgets)
find_package(QWindowKit REQUIRED COMPONENTS Widgets)

qt_add_executable(MyWidgetsApp
    main.cpp
    mainwindow.cpp
    mainwindow.h
)

target_link_libraries(MyWidgetsApp PRIVATE
    Qt6::Core
    Qt6::Gui
    Qt6::Widgets
    QWindowKit::Widgets
)

Quick application:

cmake_minimum_required(VERSION 3.19)
project(MyQuickApp LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 REQUIRED COMPONENTS Core Gui Quick Qml)
find_package(QWindowKit REQUIRED COMPONENTS Quick)

qt_add_executable(MyQuickApp
    main.cpp
)

qt_add_qml_module(MyQuickApp
    URI MyQuickApp
    VERSION 1.0
    QML_FILES Main.qml
)

target_link_libraries(MyQuickApp PRIVATE
    Qt6::Core
    Qt6::Gui
    Qt6::Quick
    Qt6::Qml
    QWindowKit::Quick
)

Configure your downstream project with the installed package path:

cmake -S . -B build -DQWindowKit_DIR=C:/Libraries/QWindowKit/lib/cmake/QWindowKit

Widgets: Minimal Window

Widgets applications must set Qt::AA_DontCreateNativeWidgetSiblings before constructing QApplication.

main.cpp:

#include <QtCore/QCoreApplication>
#include <QtWidgets/QApplication>

#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_DontCreateNativeWidgetSiblings);

    QApplication app(argc, argv);

    MainWindow window;
    window.resize(900, 600);
    window.show();

    return app.exec();
}

mainwindow.h:

#pragma once

#include <QtWidgets/QMainWindow>

namespace QWK {
class WidgetWindowAgent;
}

class QWidget;

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow() override;

private:
    void setupWindowAgent();

    QWK::WidgetWindowAgent *m_windowAgent = nullptr;
};

mainwindow.cpp:

#include "mainwindow.h"

#include <QtWidgets/QHBoxLayout>
#include <QtWidgets/QLabel>
#include <QtWidgets/QMenuBar>
#include <QtWidgets/QPushButton>
#include <QtWidgets/QWidget>

#include <QWKWidgets/widgetwindowagent.h>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    setupWindowAgent();

    auto *content = new QLabel(tr("Application content"), this);
    content->setAlignment(Qt::AlignCenter);
    setCentralWidget(content);
}

MainWindow::~MainWindow() = default;

void MainWindow::setupWindowAgent()
{
    m_windowAgent = new QWK::WidgetWindowAgent(this);
    m_windowAgent->setup(this);

    auto *titleBar = new QWidget(this);
    titleBar->setFixedHeight(40);

    auto *iconButton = new QPushButton(QStringLiteral("App"), this);
    auto *menuBar = new QMenuBar(this);
    menuBar->addMenu(tr("&File"))->addAction(tr("E&xit"), this, &QWidget::close);

    auto *titleLabel = new QLabel(windowTitle(), this);
    titleLabel->setAlignment(Qt::AlignCenter);

    auto *minButton = new QPushButton(QStringLiteral("-"), this);
    auto *maxButton = new QPushButton(QStringLiteral("□"), this);
    auto *closeButton = new QPushButton(QStringLiteral("x"), this);

    auto *layout = new QHBoxLayout(titleBar);
    layout->setContentsMargins(8, 0, 0, 0);
    layout->setSpacing(0);
    layout->addWidget(iconButton);
    layout->addWidget(menuBar);
    layout->addWidget(titleLabel, 1);
    layout->addWidget(minButton);
    layout->addWidget(maxButton);
    layout->addWidget(closeButton);

    setMenuWidget(titleBar);

    m_windowAgent->setTitleBar(titleBar);
    m_windowAgent->setSystemButton(QWK::WindowAgentBase::WindowIcon, iconButton);
    m_windowAgent->setSystemButton(QWK::WindowAgentBase::Minimize, minButton);
    m_windowAgent->setSystemButton(QWK::WindowAgentBase::Maximize, maxButton);
    m_windowAgent->setSystemButton(QWK::WindowAgentBase::Close, closeButton);
    m_windowAgent->setHitTestVisible(menuBar, true);

    connect(minButton, &QPushButton::clicked, this, &QWidget::showMinimized);
    connect(maxButton, &QPushButton::clicked, this, [this] {
        isMaximized() ? showNormal() : showMaximized();
    });
    connect(closeButton, &QPushButton::clicked, this, &QWidget::close);
}

Key points:

  • Each top-level window needs its own WidgetWindowAgent.
  • Call setup(this) as early as possible, especially before applying size constraints.
  • setTitleBar() marks the draggable title bar area.
  • Controls inside the title bar that need mouse input must be registered with setHitTestVisible(widget, true).
  • System button hints do not connect click behavior. You still connect the buttons yourself.

Widgets: Interactive Title Bar Controls

Menus should be hit-test visible:

auto *menuBar = new QMenuBar(this);
menuBar->addMenu(tr("&File"));

windowAgent->setHitTestVisible(menuBar, true);

Use the same rule for search boxes, tab bars, and tool buttons:

windowAgent->setHitTestVisible(searchEdit, true);
windowAgent->setHitTestVisible(tabBar, true);
windowAgent->setHitTestVisible(settingsButton, true);

Without this, QWindowKit treats those areas as draggable title bar space, so the controls will not receive normal mouse interaction.

Widgets: Window Buttons

Connect button behavior explicitly:

connect(minimizeButton, &QPushButton::clicked, window, &QWidget::showMinimized);

connect(maximizeButton, &QPushButton::clicked, window, [window] {
    if (window->isMaximized()) {
        window->showNormal();
    } else {
        window->showMaximized();
    }
});

connect(closeButton, &QPushButton::clicked, window, &QWidget::close);

Disable maximization:

setWindowFlag(Qt::WindowMaximizeButtonHint, false);

Create a fixed-size window:

setFixedSize(640, 420);

Quick: Register The QML Types

main.cpp:

#include <QtGui/QGuiApplication>
#include <QtQml/QQmlApplicationEngine>
#include <QtQuick/QQuickWindow>

#include <QWKQuick/qwkquickglobal.h>

int main(int argc, char *argv[])
{
    QQuickWindow::setDefaultAlphaBuffer(true);

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    QWK::registerTypes(&engine);

    engine.load(QUrl(QStringLiteral("qrc:/Main.qml")));
    if (engine.rootObjects().isEmpty()) {
        return 1;
    }

    return app.exec();
}

QQuickWindow::setDefaultAlphaBuffer(true) is usually required for transparency, blur, Mica, and glass effects. Call it before creating Quick windows.

Quick: Minimal QML Window

Main.qml:

import QtQuick
import QtQuick.Controls
import QtQuick.Layouts
import QtQuick.Window
import QWindowKit 1.0

Window {
    id: window
    width: 900
    height: 600
    visible: false
    title: "QWindowKit Quick Window"

    WindowAgent {
        id: windowAgent
    }

    ColumnLayout {
        anchors.fill: parent
        spacing: 0

        Rectangle {
            id: titleBar
            Layout.fillWidth: true
            height: 42
            color: "#242936"

            RowLayout {
                anchors.fill: parent
                spacing: 0

                Text {
                    text: window.title
                    color: "white"
                    elide: Text.ElideRight
                    verticalAlignment: Text.AlignVCenter
                    Layout.leftMargin: 12
                    Layout.fillWidth: true
                }

                Button {
                    id: minButton
                    text: "-"
                    onClicked: window.showMinimized()
                }

                Button {
                    id: maxButton
                    text: "□"
                    onClicked: {
                        if (window.visibility === Window.Maximized)
                            window.showNormal()
                        else
                            window.showMaximized()
                    }
                }

                Button {
                    id: closeButton
                    text: "x"
                    onClicked: window.close()
                }
            }
        }

        Rectangle {
            Layout.fillWidth: true
            Layout.fillHeight: true
            color: "#f5f6f8"

            Text {
                anchors.centerIn: parent
                text: "Application content"
            }
        }
    }

    Component.onCompleted: {
        windowAgent.setup(window)
        windowAgent.setTitleBar(titleBar)
        windowAgent.setSystemButton(WindowAgent.Minimize, minButton)
        windowAgent.setSystemButton(WindowAgent.Maximize, maxButton)
        windowAgent.setSystemButton(WindowAgent.Close, closeButton)
        window.visible = true
    }
}

If a control in the title bar needs mouse input, mark it as hit-test visible:

Button {
    id: menuButton
    text: "Menu"
}

Component.onCompleted: {
    windowAgent.setHitTestVisible(menuButton, true)
}

Windows Platform Effects

Windows supports several platform attributes. Set them after setup() succeeds.

windowAgent->setWindowAttribute(QStringLiteral("dark-mode"), true);
windowAgent->setWindowAttribute(QStringLiteral("mica"), true);
windowAgent->setWindowAttribute(QStringLiteral("mica-alt"), false);
windowAgent->setWindowAttribute(QStringLiteral("acrylic-material"), false);
windowAgent->setWindowAttribute(QStringLiteral("dwm-blur"), false);

Set the Windows 11 border color:

windowAgent->setWindowAttribute(QStringLiteral("dwm-border-color"), QColor("#3367d6"));

Disable the system menu:

windowAgent->setWindowAttribute(QStringLiteral("no-system-menu"), true);

Show the system menu:

windowAgent->showSystemMenu(QCursor::pos());

For Qt Quick on Windows 10/11 with D3D11 or D3D12, this workaround may help with a top white line. Keep it tied to the documented backend and Qt version constraints:

#if defined(Q_OS_WIN) && QT_VERSION >= QT_VERSION_CHECK(6, 7, 0)
qputenv("QSG_RHI_BACKEND", "d3d11");
qputenv("QT_QPA_DISABLE_REDIRECTION_SURFACE", "1");
#endif

Do not enable QT_QPA_DISABLE_REDIRECTION_SURFACE with OpenGL or Vulkan.

macOS Platform Effects

On macOS, prefer native system buttons unless you have a strong reason to draw your own.

Show native system buttons:

windowAgent->setWindowAttribute(QStringLiteral("no-system-buttons"), false);

Hide native system buttons:

windowAgent->setWindowAttribute(QStringLiteral("no-system-buttons"), true);

Enable blur:

windowAgent->setWindowAttribute(QStringLiteral("blur-effect"), QStringLiteral("dark"));
windowAgent->setWindowAttribute(QStringLiteral("blur-effect"), QStringLiteral("light"));
windowAgent->setWindowAttribute(QStringLiteral("blur-effect"), QStringLiteral("none"));

On macOS 26 and later, Liquid Glass can be enabled when available:

windowAgent->setWindowAttribute(QStringLiteral("glass-effect"), QStringLiteral("regular"));
windowAgent->setWindowAttribute(QStringLiteral("glass-corner-radius"), 24.0);
windowAgent->setWindowAttribute(QStringLiteral("glass-tint-color"), QColor(255, 255, 255, 46));

If the platform does not support an attribute, setWindowAttribute() returns false.

Linux Notes

On Linux, QWindowKit can use the Qt fallback window context and provides partial system menu support on Qt 6 Wayland/X11. Behavior varies by desktop environment and window manager.

For compatibility-first applications, consider:

-DQWINDOWKIT_FORCE_QT_WINDOW_CONTEXT=ON

Troubleshooting

Title bar controls cannot be clicked

Mark the control or its parent container as hit-test visible:

windowAgent->setHitTestVisible(button, true);

System buttons do not need an extra hit-test-visible call, but they do need a role:

windowAgent->setSystemButton(QWK::WindowAgentBase::Close, closeButton);

Windows Snap Layout does not appear

Windows 11 Snap Layout depends on the maximize button role:

windowAgent->setSystemButton(QWK::WindowAgentBase::Maximize, maxButton);

The window must also keep the maximize capability:

setWindowFlag(Qt::WindowMaximizeButtonHint, true);

When should setup() be called?

Call it early in the window constructor, before complex child widgets and size constraints when possible:

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    m_agent = new QWK::WidgetWindowAgent(this);
    m_agent->setup(this);

    setMinimumSize(640, 480);
    setupUi();
}

In QML, call it in Component.onCompleted:

Component.onCompleted: {
    windowAgent.setup(window)
    windowAgent.setTitleBar(titleBar)
    window.visible = true
}

Can an application switch back to the native frame at runtime?

Do not rely on hot switching. Once QWindowKit has taken over the window frame, recreate the window if you need a different framing mode.

Can QDockWidget use WidgetWindowAgent?

No. Install WidgetWindowAgent only on top-level windows.

Recommended Minimal Production Setup

Widgets:

QCoreApplication::setAttribute(Qt::AA_DontCreateNativeWidgetSiblings);
QApplication app(argc, argv);

Quick:

QQuickWindow::setDefaultAlphaBuffer(true);
QGuiApplication app(argc, argv);
QWK::registerTypes(&engine);

Do not copy debug environment variables from the examples into production code unless you explicitly need them.