<s>
In	O
computer	O
graphics	O
,	O
back-face	B-Algorithm
culling	I-Algorithm
determines	O
whether	O
a	O
polygon	B-General_Concept
of	O
a	O
graphical	O
object	O
is	O
drawn	O
.	O
</s>
<s>
It	O
is	O
a	O
step	O
in	O
the	O
graphical	O
pipeline	O
that	O
tests	O
whether	O
the	O
points	O
in	O
the	O
polygon	B-General_Concept
appear	O
in	O
clockwise	O
or	O
counter-clockwise	O
order	O
when	O
projected	O
onto	O
the	O
screen	O
.	O
</s>
<s>
If	O
the	O
user	O
has	O
specified	O
that	O
front-facing	O
polygons	B-General_Concept
have	O
a	O
clockwise	O
winding	O
,	O
but	O
the	O
polygon	B-General_Concept
projected	O
on	O
the	O
screen	O
has	O
a	O
counter-clockwise	O
winding	O
then	O
it	O
has	O
been	O
rotated	O
to	O
face	O
away	O
from	O
the	O
camera	O
and	O
will	O
not	O
be	O
drawn	O
.	O
</s>
<s>
The	O
process	O
makes	O
rendering	O
objects	O
quicker	O
and	O
more	O
efficient	O
by	O
reducing	O
the	O
number	O
of	O
polygons	B-General_Concept
for	O
the	O
program	O
to	O
draw	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
a	O
city	O
street	O
scene	O
,	O
there	O
is	O
generally	O
no	O
need	O
to	O
draw	O
the	O
polygons	B-General_Concept
on	O
the	O
sides	O
of	O
the	O
buildings	O
facing	O
away	O
from	O
the	O
camera	O
;	O
they	O
are	O
completely	O
occluded	O
by	O
the	O
sides	O
facing	O
the	O
camera	O
.	O
</s>
<s>
In	O
general	O
,	O
back-face	B-Algorithm
culling	I-Algorithm
can	O
be	O
assumed	O
to	O
produce	O
no	O
visible	O
artifact	B-Algorithm
in	O
a	O
rendered	O
scene	O
if	O
it	O
contains	O
only	O
closed	O
and	O
opaque	O
geometry	O
.	O
</s>
<s>
In	O
scenes	O
containing	O
transparent	O
polygons	B-General_Concept
,	O
rear-facing	O
polygons	B-General_Concept
may	O
become	O
visible	O
through	O
the	O
process	O
of	O
alpha	B-Algorithm
composition	I-Algorithm
.	O
</s>
<s>
In	O
wire-frame	B-Algorithm
rendering	I-Algorithm
,	O
back-face	B-Algorithm
culling	I-Algorithm
can	O
be	O
used	O
to	O
partially	O
address	O
the	O
problem	O
of	O
hidden	B-Algorithm
line	I-Algorithm
removal	I-Algorithm
,	O
but	O
only	O
for	O
closed	O
convex	O
geometry	O
.	O
</s>
<s>
A	O
related	O
technique	O
is	O
clipping	B-Algorithm
,	O
which	O
determines	O
whether	O
polygons	B-General_Concept
are	O
within	O
the	O
camera	O
's	O
field	O
of	O
view	O
at	O
all	O
.	O
</s>
<s>
Another	O
similar	O
technique	O
is	O
Z-culling	O
,	O
also	O
known	O
as	O
occlusion	O
culling	O
,	O
which	O
attempts	O
to	O
skip	O
the	O
drawing	O
of	O
polygons	B-General_Concept
that	O
are	O
covered	O
from	O
the	O
viewpoint	O
by	O
other	O
visible	O
polygons	B-General_Concept
.	O
</s>
<s>
"	O
inverted	O
hull	O
"	O
or	O
"	O
front	O
face	B-Algorithm
culling	I-Algorithm
"	O
can	O
be	O
used	O
to	O
simulate	O
outlines	O
or	O
toon	O
shaders	O
without	O
post-processing	O
effects	O
.	O
</s>
<s>
Reflection	O
is	O
an	O
example	O
of	O
involutory	B-Algorithm
function	I-Algorithm
(	O
with	O
respect	O
to	O
vertex	O
order	O
)	O
,	O
therefore	O
an	O
even	O
number	O
of	O
reflections	O
will	O
leave	O
the	O
triangle	O
facing	O
the	O
same	O
side	O
,	O
as	O
if	O
no	O
reflections	O
were	O
applied	O
at	O
all	O
.	O
</s>
