QPainter: Рисование части линии, ограниченной окружностью Опции

[Snake174]

Всем привет. Есть такой код:

class Widget : public QWidget
{
  Q_OBJECT
 
  QPoint mouseOldPos;
  QPoint mousePos;
  QImage *image;
 
  public:
    Widget( QWidget *parent = 0 );
    ~Widget();
 
  protected:
    void paintEvent( QPaintEvent *e );
    void draw( QPainter *painter );
    void mousePressEvent( QMouseEvent *e );
    void mouseReleaseEvent( QMouseEvent *e );
    void mouseMoveEvent( QMouseEvent *e );
 
  protected slots:
    void createImage();
};

Widget::Widget( QWidget *parent ):
  QWidget( parent ),
  image(0)
{
  setAttribute( Qt::WA_StaticContents );
  setCursor( Qt::CrossCursor );
  setMouseTracking( true );
  setFocusPolicy( Qt::WheelFocus );
  setFocus();
 
  setFixedSize( 800, 600 );
 
  QTimer::singleShot( 500, this, SLOT(createImage()) );
}
//================================================================================
=================
Widget::~Widget()
{
  if (image)
  {
    delete image;
    image = 0;
  }
}
//================================================================================
=================
void Widget::paintEvent( QPaintEvent *e )
{
  if (image)
  {
    QPainter imagePainter( image );
    imagePainter.setRenderHint( QPainter::Antialiasing, true );
    imagePainter.eraseRect( rect() );
    draw( &imagePainter );
    imagePainter.end();
 
    QPainter painter( this );
    QRect dirtyRect = e->rect();
    painter.drawImage( dirtyRect, (*image), dirtyRect );
  }
}
//================================================================================
=================
void Widget::draw( QPainter *painter )
{
  painter->save();
    painter->translate( width() / 2, height() / 2 );
    painter->setPen( QColor( 0, 0, 0, 255 ) );
    painter->drawEllipse( QPoint( 0, 90 ), 90, 90 );
  painter->restore();
 
  painter->save();
    painter->setPen( QPen( Qt::green, 2, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin ) );
    painter->drawLine( QPoint( width() / 2, height() / 2 + 90 ), mousePos );
  painter->restore();
}
//================================================================================
=================
void Widget::mousePressEvent( QMouseEvent *e )
{
  if (e->buttons() & Qt::LeftButton)
  {
    mouseOldPos = e->pos();
    update();
  }
}
//================================================================================
=================
void Widget::mouseReleaseEvent( QMouseEvent *e )
{
  update();
  e->accept();
}
//================================================================================
=================
void Widget::mouseMoveEvent( QMouseEvent *e )
{
  mousePos = e->pos();
  update();
}
//================================================================================
=================
void Widget::createImage()
{
  if (!image)
  {
    image = new QImage( size(), QImage::Format_ARGB32_Premultiplied );
    image->fill( Qt::white );
 
    update();
  }
}

Он рисует окружность и зелёную линию от центра до указателя мыши.
Нужно чтобы рисовалась часть линии, выделенная красным цветом.
В какую сторону копать?
Image