#include <QWidget>
#include <QApplication>
#include <QPainter>
#include <windows.h>

#define USE_NATIVE_PAINTING

#ifdef USE_NATIVE_PAINTING
class DavidWidget : public QWidget
{
public:
    DavidWidget() : QWidget(0) {
        setAttribute(Qt::WA_PaintOnScreen, true);

        // the next three lines are useless
        //setAttribute(Qt::WA_NoSystemBackground, true);
        //setAttribute(Qt::WA_OpaquePaintEvent, true);
        //setAutoFillBackground(false);

        setGeometry(200, 200, 200, 200);
    }
protected:
    void paintEvent(QPaintEvent *) override {
        // simulate long painting
        Sleep(500);

        HWND hwnd = (HWND)winId();
        HDC hdc = GetDC(hwnd);

        QString text("Test GDI Paint");
        RECT rect;
        GetClientRect(hwnd, &rect);

        HBRUSH hbrRed = CreateSolidBrush(RGB(255, 0, 0));
        FillRect(hdc, &rect, hbrRed);
        HBRUSH hbrBlue = CreateSolidBrush(RGB(40, 40, 255));
        HPEN bpenGreen = CreatePen(PS_SOLID, 4, RGB(0, 255, 0));
        SelectObject(hdc, bpenGreen);
        SelectObject(hdc, hbrBlue);


        Ellipse(hdc, 10, 10, rect.right - 20, rect.bottom - 20);
        SetTextAlign(hdc, TA_CENTER | TA_BASELINE);
        TextOutW(hdc, width() / 2, height() / 2, (LPCWSTR)(text.utf16()), text.size());
        ReleaseDC(hwnd, hdc);
    }
    QPaintEngine *paintEngine() const override { return 0; }
};
#endif

class NormalWidget : public QWidget
{
public:
    NormalWidget() : QWidget(0) {
        setGeometry(450, 200, 200, 200);
    }
protected:
    void paintEvent(QPaintEvent *) override {
        // simulate long painting
        Sleep(500);
        QPainter p(this);
        p.fillRect(rect(), Qt::blue);
        p.drawText(rect(), Qt::AlignCenter, "Normal widget");
    }
};

int main(int argc, char** argv)
{
    QApplication app(argc, argv);

#ifdef USE_NATIVE_PAINTING
    DavidWidget widget;
    widget.show();
#endif
    NormalWidget widget2;
    widget2.show();

    return app.exec();
}