On Sat, Jun 21, 2014 at 11:18 AM, Jean Brefort <jean.bref...@normalesup.org>
wrote:

> I know that an expose event contains a region, but this does not help,
> we use the draw event, and I don't know how to reliably access the
> region. More, it is not really easy to determine what needs to be
> redrawn from inside a draw event.
>

The cairo context you get in the draw signal is clipped to the expose
region by default, which means that cairo will do culling for you
automatically. If you need to do extra processing to determine if some
complex update method should be run based on the clip region (which is
really a big edge case -- you shouldn't need to do this!), you can use
cairo_in_clip or cairo_clip_extents.

-- 
  Jasper
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