Dark title bar when dark themed

[astrohart]

Figure 1. White title bar in dark mode.

It would be great if the titlebars of the windows on Windows 10+ could be black as well, when the app is dark themed. Dark theme looks great but I have these white titlebars sticking out everywhere which is garish, IMHO.

On Windows 10 build 1809+ and Windows 11,, the system provides an immersive dark mode feature, but Qt does not natively enable dark title bars. You can use the Windows API to force dark mode.

Use Windows API Functions
Leverage the following APIs:

• DwmSetWindowAttribute: Sets the dark mode attribute for the window.
• SetWindowTheme: Ensures the window uses a specific theme like Explorer Dark Mode.

Implementation

Create a helper function in your Qt application that uses these APIs.

#include <QMainWindow>
#include <QWindow>
#include <QDebug>
#include <windows.h>
#include <dwmapi.h>

#pragma comment(lib, "Dwmapi.lib")

namespace DarkModeHelper {

    enum DWMWINDOWATTRIBUTE {
        DWMWA_USE_IMMERSIVE_DARK_MODE = 20
    };

    bool enableDarkTitleBar(HWND hwnd, bool enabled = true) {
        if (!hwnd) {
            qDebug() << "Invalid window handle.";
            return false;
        }

        BOOL darkMode = enabled ? TRUE : FALSE;

        // Set immersive dark mode
        HRESULT hr = DwmSetWindowAttribute(
            hwnd,
            DWMWA_USE_IMMERSIVE_DARK_MODE,
            &darkMode,
            sizeof(darkMode)
        );

        if (FAILED(hr)) {
            qDebug() << "Failed to set dark mode. Error code:" << hr;
            return false;
        }

        return true;
    }
}

Step 2: Apply to Qt Windows
You can apply the enableDarkTitleBar function to your Qt windows by passing their native HWND handle. Use QWindow::winId() to get the native window handle.

Example Usage
Override the showEvent of your QMainWindow or use a helper function to apply dark mode whenever a window is shown.

#include "DarkModeHelper.h"

class DarkMainWindow : public QMainWindow {
    Q_OBJECT

public:
    DarkMainWindow(QWidget *parent = nullptr) : QMainWindow(parent) {
        // Your initialization code
    }

protected:
    void showEvent(QShowEvent *event) override {
        QMainWindow::showEvent(event);

        // Apply dark title bar
        HWND hwnd = reinterpret_cast<HWND>(this->windowHandle()->winId());
        if (!DarkModeHelper::enableDarkTitleBar(hwnd)) {
            qDebug() << "Failed to enable dark title bar.";
        }
    }
};

Considerations

1. Compatibility:

• The DwmSetWindowAttribute function is supported on Windows 10 (1809+) or later.
• Ensure your application handles older Windows versions gracefully.

2. High DPI Awareness:

• Add DPI-awareness settings to your manifest file to ensure proper scaling.

3. Performance:

• Applying dark mode dynamically might slightly affect performance. You can enable it for the best results once the window is created.

4. Consistent Styling:

• Ensure widget themes and title bars match for a seamless user experience.