An optional compiling tool that sets the portals on your map. It determines the what must be rendered in a certain area (the PVS), allowing the game to ignore parts of the map, speeding up rendering. If this process is taking too long, be sure to read up on Controlling Geometry Visibility and Compile Times on how to reduce visleafs using func_details.
The VVIS phase may be run in "fast" mode or omitted entirely to reduce the compiling time of a level, if you wish to take a quick look at how your level looks. It is strongly recommended that it is run in "normal" mode for any final map release. Note that if VVIS is not run, water will not be appear in the map correctly.
Use these in combination with expert compile mode or a batch file:
|-v (or -verbose)||Turn on verbose output (also shows more command)|
|-fast||Only do first quick pass on vis calculations.|
|-mpi||Use VMPI to distribute computations.|
|-low||Run as an idle-priority process.|
|-vproject (or -game) <directory>||Override the VPROJECT environment variable.|
|-novconfig||Don't bring up graphical UI on vproject errors.|
|-radius_override||Force a vis radius, regardless of whether an env_fog_controller specifies one.|
|-mpi_pw <pw>||Use a password to choose a specific set of VMPI workers.|
|-threads||Control the number of threads vbsp uses (defaults to the # of processors (times 2 for hyperthreading CPU's) on your machine).|
|-nosort||Don't sort portals (sorting is an optimization).|
|-tmpin||Make portals come from \tmp\<mapname>.|
|-tmpout||Make portals come from \tmp\<mapname>.|