\section{Scene Description Files}
\index{scene description files}
  At the present time, scene description files are very simple.  
The parser can't handle multiple file scene descriptions, although they
may be added in the future.  Most of the objects and their scene description
are closely related to the Tachyon API 
{\em (See the API docs for additional info.)}

\subsection{Basic Scene Requirements}
  Unlike some other ray tracers out there, Tachyon requires that you 
specify most of the scene parameters in the scene description file itself.
If users would rather specify some of these parameters at the command line,
then I may add that feature in the future.  
A scene description file contains keywords, and values associated or grouped
with a keyword.  All keywords can be in caps, lower case, or mixed case
for the convenience of the user.  File names and texture names are 
normally case-sensitive, although the behavior for file names is 
operating system-dependent.  All values are either character strings, or
floating point numbers.  In some cases, the presence of one keyword will
require additional keyword / value pairs. 

  At the moment there are several keywords with values, 
that must appear in every scene description file.  
Every scene description file must begin with the 
{\bf BEGIN\_SCENE} keyword, and end with the {\bf END\_SCENE} keyword.
All definitions and declarations of any kind must be inside the 
{\bf BEGIN\_SCENE}, {\bf END\_SCENE} pair.
The {\bf RESOLUTION} keyword is followed by an x resolution
and a y resolution in terms of pixels on each axis.  There are currently 
no limits placed on the resolution of an output image other than the
computer's available memory and reasonable execution time.
An example of a simple scene description skeleton is show below:
\begin{verbatim}
BEGIN_SCENE
  RESOLUTION 1024 1024 
...
...  Camera definition..
...
...  Other objects, etc..
...

END_SCENE
\end{verbatim}

\input{camera}

\subsection{Including Files}
\index{include files}
The {\bf INCLUDE} keyword is used anywhere after the camera description,
and is immediately followed by a valid filename, for a file containing
additional scene description information.  The included file is opened,
and processing continues as if it were part of the current file, until
the end of the included file is reached.  Parsing of the current file
continues from where it left off prior to the included file.  

\subsection{Scene File Comments}
\index{scene file comments}
The {\bf $\#$} keyword is used anywhere after the camera description, and 
will cause Tachyon to ignore all characters from the {\bf $\#$} to the end 
of the input line.  The {\bf $\#$} character must be surrounded by whitespace
in order to be recognized.  A sequence such as {\bf $\#\#\#$} will not be
recognized as a comment.

\input{lights}

\input{fog}

\input{objects}

\input{texture}


