
\subsection{Atmospheric effects}
\RAY\ currently only implements one atmospheric effect, 
simple distance-based fog.

\subsubsection{Fog}
\index{fog}
\RAY\ provides a simple distance-based fog effect intended to provide
functionality similar to that found in OpenGL, for compatibility with
software that requires an OpenGL-like fog implementation.  Much like
OpenGL, \RAY\ provides linear, exponential, and exponential-squared fog.

\begin{verbatim}
  FOG 
    LINEAR START 0.0  END 50.0  DENSITY 1.0  COLOR 1.0 1.0 1.0
\end{verbatim}

\begin{verbatim}
  FOG 
    EXP START 0.0  END 50.0  DENSITY 1.0  COLOR 1.0 1.0 1.0
\end{verbatim}

\begin{verbatim}
  FOG 
    EXP2 START 0.0  END 50.0  DENSITY 1.0  COLOR 1.0 1.0 1.0
\end{verbatim}



