+ virtual QMenu* create_context_menu(QWidget *parent);
+
+protected:
+ /**
+ * Gets the y-offset of the axis.
+ */
+ int get_y() const;
+
+ /**
+ * Gets the text colour.
+ * @remarks This colour is computed by comparing the lightness
+ * of the trace colour against a threshold to determine whether
+ * white or black would be more visible.
+ */
+ QColor get_text_colour() const;
+
+ /**
+ * Paints a zero axis across the viewport.
+ * @param p the QPainter to paint into.
+ * @param y the y-offset of the axis.
+ * @param left the x-coordinate of the left edge of the view.
+ * @param right the x-coordinate of the right edge of the view.
+ */
+ void paint_axis(QPainter &p, int y, int left, int right);
+