Brushes are main elements of each map. Basicly anything that isn't a model, misc or a curve is a brush. They are mostly rectangular but can appear in any shape. Brushes are serving as walls, floors and small details. With the appropriate shader put on them, Brushes can behave like water, lava sky or slime.
Brushes have 2 kinds:
- Structural- this ones blocks vis* and are used to create the walls and floors that go into the void
- Detail- this ones don't block vis* which means that they cannot separate the map from the void, but details are also taking much less space in map files and take much less time to compile. ( To make brush detail select it and us key combination [ctrl + M] )
*-vis is a stage in compilation process in which compiling program handles map parts sharing them with areaportals, hint brushes and walls. If it founds any leak going into the void it returns an error. Detail brushes don't block: the -vis process just omits them saving time, but this also means that if it finds void while going through detail brushes the compilation will result in an error.
Brushes are created by simply pressing and dragging our mouse in the 'grid' view in mapping programs (like GTKRadiant).