+ /**
+ * Paints the signal into a QGLWidget.
+ * @param widget the QGLWidget to paint into.
+ * @param rect the rectangular area to draw the trace into.
+ * @param scale the scale in femtoseconds per pixel.
+ * @param offset the time to show at the left hand edge of
+ * the view in femtoseconds.
+ **/
+ virtual void paint(QGLWidget &widget, const QRect &rect,
+ uint64_t scale, int64_t offset) = 0;