When you compile you level you mayhave noticed that the q3map -vis compilation takes quite a while (possibly hours and hours!!!), What -vis is doing is working out what can be seen from wherever the player might be stood. (and therefore what the engine renders..)

The proper use of detail and structural brushes will help keep those -vis compilations at a minimum. -vis compliation will ignore any detail brushes and only "see" structural brushes...

The main walls of the map (and floors and ceilings and skies...!) should be structural brushes, but stairs, trimmings and details can all be set to detail brushes. It's important to remember that detail brushes are see-thru as far as vis is concerned and cannot be used to seal the level, cos they'll cause a leak.

How can I make VIS more efficient? (and reduce -vis processing time)

The time -vis takes is roughly proportional to the number of Portals in the map. The number of portals is displayed when you start VIS, as "numportals xxxx". The visdatasize is the size the PVS table takes up in the mapname.bsp file - this is limited to around 2MB.
A lot of Leaf Nodes means a lot of Portals. A lot of Portals means a long vis time.
The number of Leaf Nodes depends entirely on the complexity of the BSP.
Solution: detail brushes - Making a brush detail will stop it from affecting the BSP Tree, reducing the number of Leaf Nodes formed.
To make any brush a detail brush, select it and press ctrl+m or Selection > Make detail. Toggle viewing of detail brushes with ctrl+D or use the View > Show menu.


The drawback of wide use of detail is that over-simplifying the Leaf Nodes can hurt your visibility efficiency (see visibility summary).
Solution: HINT brushes - A Hint brush (common/hint) will be invisible in Q3, but is structural, so it will affect the BSP Tree and create more Leaf Nodes. This gives you a lot of control over where the Leaf Nodes are created. Placing a hint brush in an area of open space will force creation of a Leaf Node within the area of that hint brush. Hints can also intersect with other structural solid brushes or Hints, creating multiple Leaf Nodes or isolating groups of Leaf Nodes.
Hint brushes use a shader which makes the brushes nonsolid and nodraw, called common/hint.


Hints are best used to make large axial cuts along planes shared by other structural brushes, to maximise the amount of area hidden by each vis-blocking structural brush, by minimising the number and size of the Leaf Nodes visible.

Intelligent use of detail and Hint brushes in combination can reduce vis time and r_speeds in almost any map. However the map must be designed from the start with this in mind. Redoing an inneffiently made map is a lot of work.
Note: Making a brush detail will stop it from blocking visibility, so don't make your vis-blocking walls into detail brushes.