+ double scale, double offset) = 0;
+
+ /**
+ * Paints the signal label into a QGLWidget.
+ * @param p the QPainter to paint into.
+ * @param rect the rectangular area to draw the label into.
+ */
+ virtual void paint_label(QPainter &p, const QRect &rect);
+
+protected:
+
+ /**
+ * Get the colour of the logic signal
+ */
+ virtual QColor get_colour() const = 0;
+
+ /**
+ * When painting into the rectangle, calculate the y
+ * offset of the zero point.
+ **/
+ virtual int get_nominal_offset(const QRect &rect) const = 0;