[cairo] Answering my own queston - Region_t - Re: one question answered, and another comes (Re: FT_Bitmap_Convert, and FreeType's bitmap format vs Cairo's)

Hin-Tak Leung htl10 at users.sourceforge.net
Tue Apr 25 13:27:26 UTC 2017

To answer my own question again - cairo has a cairo_region_intersect() and cairo_region_intersect_rectangle().
This is almost as good as the numpy vector sum. (the vector sum can pack tighter).

Unfortunately these are only exposed to python via either a python3-specific custom patch which Ubuntu/Debian carries
(Fedora certainly does not), or use the recently merged pycairo 1.11 released a couple of weeks ago.
(or qahirah). I'll go the pycairo 1.11+ path.

Not quite sorry for the noise - Google doesn't really have answers to these :-).

On Tue, 25/4/17, Hin-Tak Leung <htl10 at users.sourceforge.net> wrote:

One of freetype-py's drawing example
 uses a vector sum between a clip of the drawing surface with
 the current drawing pattern to see if we are drawing over
 something that's already drawn in this single line:
 if (I[y-h//2:y-h//2+h,
 x-w//2:x-w//2+w,0] * L).sum() == 0:
 i.e. this calculates if L will draw on
 anything previously drawn in I. I am trying to figure out
 how to do this in cairo.
 How does one check if two shapes
 overlap, or two paths intersect, in cairo?

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