The basic piece of geometry is a brush, which in the editor is defined as a
single piece of 3-dimensional geometry such as a wall, staircase, or hollow box.
Brushes are made up of faces (sides) whose attributes can be changed independently of the brush. The
editor supports three basic types of brushes: solid, hollow, and cut.
Solid brushes such as walls, floors, and staircases make up most of the
geometry in a level.
Hollow brushes have the same shapes as do solid brushes, but they're just thin
shells. You can configure the wall thickness (called the hull size), and as
you resize the brush, the hull size remains constant. If the wall thickness
didn't remain constant as you resized the brush, it would be very difficult to
create levels with constant-thickness walls.
Cut brushes are brushes that remove material from the level. You can use cut
brushes to hollow out solid objects, cut doors and windows in walls, or to build
intricate complex forms of arbitrary geometry. There are two ways to make a
cut brush. You can select the Cut Brush checkbox in the brush primitive's
template, or you can select an existing brush, and click the Carve toolbar button.
A brush has attributes that describe its contents, visibility, and whether or
not it can be collided with. You change these attributes in the Brush
Attributes dialog. You can also change the texture that is applied to the entire
brush, or you can texture each brush face individually.
Brushes