A general result concerning gluon styles is that the \bs CURLY
(\bs FLIPPEDCURLY) and the \bs CENTRAL (\bs FLIPPEDCENTRAL)
configurations are frequently more appealing than the \bs REG (\bs FLIPPED)
configuration if both diagonal and non-diagonal  gluons appear in
the same diagram.  The reason is that slanted (eg. NW) gluons may only
be drawn in a \bs CENTRALGLUON sort of style (but still called \bs REG)
and the \bs CURLY style is also very similar to this from a spacing and
size viewpoint.  Another important point is that gluons are by far the
most {\em expensive} sort of lines to draw from the viewpoint of
\TeX's internal memory (independent of the memory of the driving system).
For this reason you will quickly discover that diagrams involving a great
many gluons tend to run out of \TeX\ capacity.  One way to alleviate
the problem is to use \LaTeX's `\bs include' facility which allows you
to divide up a long program into a series of small ones connected by 
{\em auxiliary} files which are automatically produced when \LaTeX\ is run.
Dozens of photonic, scalar and fermionic diagrams may be constructed
for the same memory usage of a single hadronic diagram.

A number a further features exist which will be mentioned here and elaborated
on in subsequent chapters.  Thus far no multi-gluon vertices have been
drawn.  Using the techniques presented here it is obvious how this
may be done - draw  a gluon at (\bs gluonbackx,\bs gluonbacky),
attaching it at the rear of the last gluon.  The results are not always
\ae sthetically appealing so a number a pre-drawn vertices are available.
This is the subject of chapter 3.  A further feature has to do with 
attaching gluons end-to-end.  This may not seem necessary but is often
desirable (see the exercise below).  The problem is illustrated by the
following file:

\begin{verbatim}

\begin{picture}(25000,7000)
\drawline\gluon[\E\REG](0,3000)[4]
\drawline\gluon[\E\REG](\pbackx,\pbacky)[4]

\drawline\gluon[\E\CENTRAL](15000,3000)[4]
\drawline\gluon[\E\CENTRAL](\pbackx,\pbacky)[4]
\end{picture}

\end{verbatim}
giving us:

\begin{picture}(25000,7000)
\drawline\gluon[\E\REG](0,4000)[4]
\drawline\gluon[\E\REG](\pbackx,\pbacky)[4]

\drawline\gluon[\E\CENTRAL](15000,4000)[4]
\drawline\gluon[\E\CENTRAL](\pbackx,\pbacky)[4]
\end{picture}

For gluons in the N,S, E and W directions \bs REG, \bs CURLY, \bs FLAT
and \bs SQUASHED configurations may be attached end-to-end trivially.
For \bs CENTRAL gluons and all gluons in the NW, NE, SE and SW directions
the connection is imperfect.  The \verb@\gluonlink@ command, discussed
in chapter four, alleviates this:

\begin{verbatim}

\begin{picture}(10000,5000)
\drawline\gluon[\E\CENTRAL](0,3000)[4]\gluonlink
\drawline\gluon[\E\CENTRAL](\pbackx,\pbacky)[4]
\end{picture}
\end{verbatim}
\begin{picture}(10000,5000)
\drawline\gluon[\E\CENTRAL](0,3000)[4]\gluonlink
\drawline\gluon[\E\CENTRAL](\pbackx,\pbacky)[4]
\end{picture}
\vskip 0.15in
The {\em stemmed} option demonstrated for photons is also available for
gluons and is of significantly more interest, especially for those of the
\bs CENTRAL variety:
\vskip 0.2in  \hskip 1.25in
\begin{picture}(25000,10000)
\drawline\gluon[\E\CENTRAL](0,7000)[6]
\advance \gluonfrontx by -800
\put(\gluonfrontx,2000){UNSTEMMED}
\drawline\fermion[\NW\REG](\pfrontx,\pfronty)[2000]
\drawline\fermion[\SW\REG](\pfrontx,\pfronty)[2000]
\drawline\fermion[\NE\REG](\gluonbackx,\gluonbacky)[2000]
\drawline\fermion[\SE\REG](\gluonbackx,\gluonbacky)[2000]
\stemmed\drawline\gluon[\E\CENTRAL](13000,7000)[6]
\gluonbacky=\pbacky   \gluonbackx=\pbackx
\advance \gluonfrontx by 400
\put(\gluonfrontx,2000){STEMMED}
\drawline\fermion[\NW\REG](\pfrontx,\pfronty)[2000]
\drawline\fermion[\SW\REG](\pfrontx,\pfronty)[2000]
\drawline\fermion[\NE\REG](\gluonbackx,\gluonbacky)[2000]
\drawline\fermion[\SE\REG](\gluonbackx,\gluonbacky)[2000]
\end{picture}
\vskip 0.34in
The chief advantage of \bs CENTRAL gluons is that their endpoints are
approximately on the axis along which the line is being drawn.
This may be artificially achieved for other styles using the \bs gluoncap
command.
The {\it capped} option is unique to gluons.  It is employed to make
gluon lines of a non-central variety (\ie\ those which do not terminate
near the axis of the gluon line) appear centralized.  An example is:
\vskip 0.2in \hskip 0.71in
\begin{picture}(25000,10000)
\THICKLINES
\put(4000,7000){\circle{3000}}
\drawline\gluon[\E\REG](5400,7000)[4]
\drawline\fermion[\NE\REG](\gluonbackx,\gluonbacky)[2000]
\drawline\fermion[\SE\REG](\gluonbackx,\gluonbacky)[2000]
\drawline\gluon[\W\FLIPPED](2600,7000)[4]
\drawline\fermion[\NW\REG](\gluonbackx,\gluonbacky)[2000]
\drawline\fermion[\SW\REG](\gluonbackx,\gluonbacky)[2000]
\advance \gluonfrontx by -1500
\put(\gluonfrontx,2000){UNCAPPED}
%\put(24000,7000){\circle{3000}}
%\drawline\gluon[\E\REG](25500,7000)[4]\gluoncap
%\drawline\fermion[\NE\REG](\gluonbackx,\gluonbacky)[2000]
%\drawline\fermion[\SE\REG](\gluonbackx,\gluonbacky)[2000]
%\drawline\gluon[\W\FLIPPED](22500,7000)[4]\gluoncap
%\drawline\fermion[\NW\REG](\gluonbackx,\gluonbacky)[2000]
%\drawline\fermion[\SW\REG](\gluonbackx,\gluonbacky)[2000]
%\advance \gluonfrontx by -900
%\put(\gluonfrontx,2000){CAPPED}
\put(24000,7000){\circle{3000}}
\startphantom
\drawline\gluon[\E\REG](0,0)[2]\gluoncap
\stopphantom
\pbackx=22600 \pbacky=7000
\multiply \plengthx by -1    \multiply \plengthy by -1
\advance \pbackx by \plengthx  \advance \pbacky by \plengthy
\drawline\gluon[\E\REG](\pbackx,\pbacky)[2]\gluoncap
%\advance\gluonfrontx by 75
\drawline\gluon[\W\FLIPPED](\gluonfrontx,\gluonfronty)[2]\gluoncap
\drawline\fermion[\NW\REG](\gluonbackx,\gluonbacky)[2000]
\drawline\fermion[\SW\REG](\gluonbackx,\gluonbacky)[2000]
\gluonbackx=25400 \gluonbacky=7000
\multiply \gluonlengthx by -1    \multiply \gluonlengthy by -1
\advance \gluonbackx by \gluonlengthx  \advance \gluonbacky by \gluonlengthy
\drawline\gluon[\W\FLIPPED](\gluonbackx,\gluonbacky)[2]\gluoncap
%\advance\gluonfrontx by -75
\drawline\gluon[\E\REG](\gluonfrontx,\gluonfronty)[2]\gluoncap
\drawline\fermion[\NE\REG](\gluonbackx,\gluonbacky)[2000]
\drawline\fermion[\SE\REG](\gluonbackx,\gluonbacky)[2000]
\advance \gluonfrontx by -6800
\put(\gluonfrontx,2000){CAPPED}
\THINLINES
\end{picture}
\vskip 0.2in

There are a number of subtleties involved with the above
features which is why their discussion is being postponed.
Finally a primitive \bs drawloop\footnote{currently only available for gluons}
command allows a gluon loop to be drawn.
These are also discussed in chapter four.

We conclude with the following exercises.  First draw the following
which uses \bs REG style gluons:

\begin{picture}(20000,20000)
\thinlines
\drawline\gluon[\E\REG](18000,18000)[4]
\drawline\fermion[\S\REG](\pfrontx,\pfronty)[\gluonlengthx]
\thicklines
\drawline\gluon[\E\REG](\gluonbackx,\gluonbacky)[4]
\drawline\fermion[\S\REG](\pbackx,\pbacky)[\gluonlengthx]
\thinlines
\drawline\fermion[\S\REG](\pbackx,\pbacky)[\gluonlengthx]
\drawline\gluon[\W\REG](\fermionbackx,\fermionbacky)[4]
\thicklines
\drawline\gluon[\W\REG](\gluonbackx,\gluonbacky)[4]
\drawline\fermion[\N\REG](\pbackx,\pbacky)[\fermionlength]
\end{picture}
\vskip -0.15in
How would you draw this using \bs CENTRAL gluons {\it without} invoking the
\bs gluonlink command?
%  Answer:  each gluon should be drawn in 3 overlapping pieces:
%\drawline\gluon[\E\CENTRAL](0,0)[5]
%\drawline\gluon[\E\CENTRAL](0,0)[4]
%\thicklines\drawline\gluon[\E\CENTRAL](0,0)[4]
