<s>
The	O
Greiner-Hormann	O
algorithm	O
is	O
used	O
in	O
computer	O
graphics	O
for	O
polygon	O
clipping	B-Algorithm
.	O
</s>
<s>
It	O
performs	O
better	O
than	O
the	O
Vatti	B-Algorithm
clipping	I-Algorithm
algorithm	I-Algorithm
,	O
but	O
cannot	O
handle	O
degeneracies	O
.	O
</s>
<s>
It	O
can	O
be	O
trivially	O
generalized	O
to	O
compute	O
other	O
Boolean	B-Algorithm
operations	I-Algorithm
on	I-Algorithm
polygons	I-Algorithm
,	O
such	O
as	O
union	O
and	O
difference	O
.	O
</s>
<s>
It	O
considers	O
regions	O
with	O
odd	O
winding	O
number	O
to	O
be	O
inside	O
the	O
polygon	O
;	O
this	O
is	O
known	O
as	O
the	O
even	B-Algorithm
–	I-Algorithm
odd	I-Algorithm
rule	I-Algorithm
.	O
</s>
<s>
This	O
is	O
accomplished	O
by	O
evaluating	O
the	O
even	B-Algorithm
–	I-Algorithm
odd	I-Algorithm
rule	I-Algorithm
at	O
the	O
first	O
vertex	O
,	O
which	O
allows	O
you	O
to	O
know	O
whether	O
the	O
first	O
vertex	O
is	O
inside	O
or	O
outside	O
the	O
other	O
polygon	O
.	O
</s>
