<s>
Brushes	O
are	O
templates	O
used	O
in	O
some	O
3D	O
video	O
game	O
engines	O
,	O
such	O
as	O
the	O
Quake	B-Application
engine	I-Application
,	O
its	O
derivatives	O
the	O
GoldSrc	B-Application
and	O
Source	B-Application
game	I-Application
engines	I-Application
,	O
or	O
the	O
Unreal	B-Operating_System
Engine	I-Operating_System
,	O
to	O
construct	O
levels	O
.	O
</s>
<s>
Brushes	O
can	O
be	O
primitive	B-Algorithm
shapes	I-Algorithm
(	O
such	O
as	O
cubes	O
,	O
spheres	O
and	O
cones	O
)	O
,	O
pre-defined	O
shapes	O
(	O
such	O
as	O
staircases	O
)	O
,	O
or	O
custom	O
shapes	O
(	O
such	O
as	O
prisms	O
and	O
other	O
polyhedra	O
)	O
.	O
</s>
<s>
During	O
the	O
map	B-Application
compilation	I-Application
process	O
,	O
brushes	O
are	O
turned	O
into	O
meshes	O
that	O
can	O
be	O
rendered	O
by	O
the	O
game	O
engine	O
.	O
</s>
