In Worldcraft/
Hammer/
J.A.C.K,
VisGroups (from
Visibility
Groups) are a method of organizing objects in the level editor's native formats (.rmf for Hammer, .jmf for J.A.C.K.), analogous to layers in image editing softwares*. It provides mappers the ability to:-
- assign a specific colour to all objects in the visgroup.
- switch visibility of objects assigned to visgroups on/off to organize and de-clutter the visual space.
- skip exporting of objects assigned to visgroups that have been switched off. A checkbox in the Run Map dialogs controls this behaviour.
It should be noted that in Hammer 3.x's .rmf format an object (brushwork or point entities) can be assigned to only one visgroup, while in J.A.C.K.'s .jmf they can be part of any number of visgroups.
Also, it has no bearing on the exported .map file apart from the last point above (.map format have no visgroups) and thus no influence on the working of the compiled .bsp i.e. objects in a visgroup don't behave any different if they're in a different visgroup or in none.
* Unlike layers in image editors, objects in Hammer/J.A.C.K. need not be part of any visgroup. Also arbitrary objects can be hidden using the Hide Object command/button regardless of their membership of any visgroup.
Nothing to do with VIS...