>>>>> On Tue, 16 Apr 2013 09:17:33 +0900, YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp> said:

>> Sorry, I don't understand.  I was asking why the code that makes
>> the corners of the window round cannot be run directly from the GUI
>> drawing code of the Mac display back-end, e.g., from the update_end
>> method.  Why does it _have_ to be run from the expose handler?

> I actually tried to round the bottom corners by calling some
> undocumented API from update_end_hook in the very first trial.
> Repeated rounding made the corner shaper because of anti-aliasing
> there.

s/shaper/sharper/

The attached images shows the difference.