extern void plot(struct graphics_context *gc, cairo_rectangle_int_t *drawing_area, struct dive *dive);
extern void set_source_rgb(struct graphics_context *gc, double r, double g, double b);
extern void plot(struct graphics_context *gc, cairo_rectangle_int_t *drawing_area, struct dive *dive);
extern void set_source_rgb(struct graphics_context *gc, double r, double g, double b);