[cairo] Problem clearing edge of a clip region

[Ian Britten]

Bill Spitzak wrote:
> I'm pretty certain this is antialiasing causing it. Clearing an 
> antialised clip region will only partially clear the edge pixels.

That's what I had suspected/feared.
I guess I would have hoped that a 'clear' operation would have
cleared any pixels that were 'drawn' - Sortof like a symmetric, but
inverse, operation.

> You should see if you can round up your clip region to pixel boundaries.

In the example I gave, the context has a default/1-1 scaling on it,
and the clip points are all integral.
However, that's not really the problem I'm seeing.  The problem is
all the intermediate (diagonal) pixels between the path points that
I'm seeing aren't being cleared, and hence my question.

Thanks,
Ian