Brush

A brush is a convex 3D shape created with Hammer's Block Tool. Brushes are used by level designers to define the shape of the environment and to create brush entities. When a map is compiled, VBSP converts brush faces into polygons. The resulting brush models are stored within the BSP file and considered to be part of the world, or another brush entity.

In comparison to studio models, brushes are:
 * Easy to make unique
 * Low-detail and
 * Lit by lightmaps (usually)
 * Rigid (cannot be animated except for basic movement)

VBSP enforces these limits on brushes: Any brush and its sides that need to be in the BSP will be counted towards the limits, visible or invisible. Faces textured with nodraw do not count toward the limit.
 * 8192 brushes
 * 128 faces on a single brush
 * 32768 faces overall
 * 65536 planes, after VBSP is finished diving all brush faces into triangles (the number of triangles on a face is equal to the number of face edges minus two)