[cairo] hit detection for paths

[Sven Herzberg]

Hi,

  I'd like to propose my idea for hit detection implementation (which is
- at all - really simple, no extra surfaces, etc.).

IMHO, we just need this function:

double cairo_path_distance(cairo_path_t* path,
                           cairo_fill_rule_t fill_rule,
                           double       x,
                           double       y);

This would provide all the information that I would need for cairo-based
hit-detection.

Pros:
 * simple API
 * works for every cairo_path_t

Cons:
 * no alpha support (i think application developers can care for this)
 * cairo_fill_rule_t needs to be added to that library for not needing
   a cairo_t to detect this

Regards,
  Sven