Subject:   -37- 1.2 libpf Multiple EarthSky fog
Date: 8 Apr 1994 00:00:01 EST

  When using multiple pipes which share pfEarthSky fog set by
  pfESkyFog, the fog may appear to change densities and flash.
  Workaround: to guarantee that pfClearChan is not called
  simultaneously by more than one pipe.  This may be accomplished with
  a hardware spin lock (see usnewlock)