Russian Qt Forum

#include <QtGui>
//------------------------------------------------------------------
class ShadowWidget : public QWidget
{
public:
    ShadowWidget(QWidget * nestedWidget, QWidget *parent = 0, int shadowWidth = 10, int radius = 5)
        : QWidget(parent, Qt::SplashScreen)
        , m_nested(nestedWidget)
        , m_shadowWidth(shadowWidth)
        , m_radius(radius)
    {
        this->setWindowOpacity(0.4);
    }

    void updateSize()
    {
        move(m_nested->pos());
        setFixedSize(m_nested->size().width() + m_shadowWidth, m_nested->size().height() + m_shadowWidth);
    }

protected:
    void paintEvent       (QPaintEvent  *event)
    {
        Q_UNUSED(event);
        QPainter painter(this);
        painter.fillRect(rect(), QBrush(Qt::black));
    }

    void resizeEvent      (QResizeEvent *event)
    {
        qDebug() << Q_FUNC_INFO << " pos() = " << pos();
        Q_UNUSED(event);
        QBitmap bitmap(rect().size());
        bitmap.fill(Qt::white);
        bitmap.createMaskFromColor(Qt::white, Qt::MaskOutColor);
        QPainter painter(&bitmap);
        
        QPainterPath opaquePath;
        opaquePath.addRoundRect(rect().adjusted(m_shadowWidth, m_shadowWidth, 0, 0), m_shadowWidth, m_shadowWidth);
        painter.fillPath(opaquePath, Qt::black);

        QPainterPath transparentPath;
        transparentPath.addRoundRect(rect().adjusted(0, 0, -m_shadowWidth, -m_shadowWidth), m_radius, m_radius);
        painter.fillPath(transparentPath, Qt::white);
        
        setMask(bitmap);
    }

private:
    QWidget *m_nested;
    int m_shadowWidth;
    int m_radius;
};
//------------------------------------------------------------------
class CustomDialog : public QDialog
{
Q_OBJECT
public:

    CustomDialog(QWidget *parent = 0, int radius = 5)
        : QDialog(parent, Qt::FramelessWindowHint)
        , m_shadow(new ShadowWidget(this, parent))
        , m_radius(radius)
    {
    }

    ~CustomDialog()
    {
        delete m_shadow;
    }
   
protected:
	/// event handlers
    void mousePressEvent  (QMouseEvent  *event)
    {
        const bool leftButtonPressed(event->button() == Qt::LeftButton);
        if (!leftButtonPressed || !rect().contains(event->pos()))
            return;
        m_moving = true;
        m_dragPosition = event->globalPos() - frameGeometry().topLeft();
        event->accept();
        return;
    }

    void mouseReleaseEvent(QMouseEvent  *event)
    {
        Q_UNUSED(event);
        m_moving = false;
    }

    void mouseMoveEvent   (QMouseEvent  *event)
    {
        if (!m_moving) 
            return;

        move(event->globalPos() - m_dragPosition);
        m_shadow->updateSize();
        m_dragPosition = event->globalPos() - frameGeometry().topLeft();
        event->accept();
    }

	void paintEvent       (QPaintEvent  *event)
    {
        Q_UNUSED(event);
        QPainter painter(this);
        QPen pen(QColor(Qt::green), 3);
        painter.setPen(pen);
        painter.drawRoundRect(rect().adjusted(0, 0, -1, -1), m_radius, m_radius);
        m_shadow->updateSize();
        m_shadow->show();
    }

    void resizeEvent      (QResizeEvent *event)
    {
        Q_UNUSED(event);
        QBitmap bitmap(rect().size());
        bitmap.fill(Qt::white);
        bitmap.createMaskFromColor(Qt::white, Qt::MaskOutColor);
        QPainter painter(&bitmap);
        painter.setPen(Qt::black);
        QPainterPath path;
        path.addRoundRect(rect(), m_radius, m_radius);
        painter.fillPath(path, Qt::black);
        setMask(bitmap);
        m_shadow->update();
    }

private:

	bool m_moving;
	QPoint           m_dragPosition;
    ShadowWidget *m_shadow;
    int m_radius;
};
//------------------------------------------------------------------
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    CustomDialog dialog;
    dialog.setFixedSize(100, 60);
    dialog.show();
    app.exec();
}

#include "main.moc"

void paintEvent       (QPaintEvent  *event)
	{
		m_shadow->updateSize();
		m_shadow->show();
	}

	void resizeEvent      (QResizeEvent *event)
	{
		m_shadow->update();
	}