[cairo] Hit detect surface?

[Vladimir Vukicevic]

On 2/28/06, Bill Spitzak <spitzak at d2.com> wrote:
> This can be used to see if some arbitrary Cairo code draws anything (or
> anything non-transparent) in a parallelogram-shaped region. To do
> accurate hit detection the caller should loop, using smaller areas each
> time, until only one object is hit or a minimum size is reached.

This sounds impossible to implement with any surface but the image
backend -- cairo has no knowledge of what pixels actually get touched
by underlying platform methods.  What are the use cases for this?

    - Vlad