void xrchart_draw_histogram (const struct chart_item *, cairo_t *,
struct xrchart_geometry *);
void xrchart_draw_np_plot (const struct chart_item *, cairo_t *,
void xrchart_draw_histogram (const struct chart_item *, cairo_t *,
struct xrchart_geometry *);
void xrchart_draw_np_plot (const struct chart_item *, cairo_t *,