Game Development Reference
So say you wanted to create a room. You could place six addiive cubes making up the
walls, loor, and ceiling, but there's a beter way to do it. In addiion to addiive, unreal has
subtracive, and it does just what you'd think—it carves a hole in addiive. Select the builder
brush, move it so that it's parially intersecing with your addiive brush, and click
CSG : Subtract .
If you move the builder brush out of the way, you'll see that there's now a chunk taken out
of your cube, and there's a yellow subtracive cube in the 2D view.
Try moving the subtracive brush around. You will again need to rebuild geometry in order
for the changes to update in the 3D view.
Also, you can clone your addiive or subtracive brushes by copying-and-pasing them ( ctrl+c ,
ctrl+v ), or by alt+ dragging one of the movement handles. Play around a litle more, intersect
some more shapes, and rebuild. Get a feeling for the tools.