A: This calligraphic masterpiece was created by:
\begin{picture}(28000,8000)
%T:
\drawline\gluon[\N\CENTRAL](0,0)[5]
\global\Yone=\gluonbacky
\drawline\fermion[\W\REG](\gluonbackx,\gluonbacky)[4000]
\drawline\fermion[\E\REG](\gluonbackx,\gluonbacky)[4000]
\global\advance\pbackx by 1000
%H:
\drawline\fermion[\N\REG](\pbackx,\gluonfronty)[\gluonlengthy]
\drawline\photon[\E\REG](\pmidx,\pmidy)[5]
\drawline\fermion[\N\REG](\pbackx,\gluonfronty)[\gluonlengthy]
\global\advance\pbackx by 1000
%E:
\drawline\fermion[\N\REG](\pbackx,\gluonfronty)[\gluonlengthy]
\global\advance\pmidy by -300
\drawline\gluon[\E\FLIPPEDCURLY](\pmidx,\pmidy)[4]
\global\advance\plengthx by 500
\drawline\fermion[\E\REG](\gluonfrontx,0)[\plengthx]
\drawline\fermion[\E\REG](\gluonfrontx,\Yone)[\plengthx]
\global\advance\pbackx by 4000
%O:
\drawloop\gluon[\NW 8](\pbackx,300)
\global\advance\loopbackx by 5500
%R:
\drawline\gluon[\S\CURLY](\loopbackx,\Yone)[3]
\global\Xone=\boxlengthy \double\Xone \multroothalf\Xone
\put(\pmidx,\pmidy){\oval(\Xone,\boxlengthy)[r]}
\drawline\fermion[\S\REG](\pbackx,\pbacky)[\pbacky]
\global\advance\pfrontx by 500
\global\advance\pfronty by 50
\drawline\photon[\SE\REG](\pfrontx,\pfronty)[4]
%Y:
\global\advance\pbackx by 2600
\drawline\photon[\N\CURLY](\pbackx,0)[3]
\global\Ytwo=\Yone
\negate\plengthy
\global\advance\Ytwo by \plengthy
\double\Ytwo \multroothalf\Ytwo
\drawline\fermion[\NE\REG](\photonbackx,\photonbacky)[\Ytwo]
\drawline\fermion[\NW\REG](\photonbackx,\photonbacky)[\Ytwo]
\end{picture}
B:
The `balloon in the tree' diagram:
\begin{picture}(28000,28000)
\THICKLINES
%set up position of bottom of loop
\startphantom
\drawloop\gluon[\NE 0](0,0)
\stopphantom
\global\Xone=\loopfrontx % diameter of `true' loop
\drawloop\gluon[\S 7](12000,18000)
\global\Xtwo=\gluonbackx
\global\Ytwo=\gluonbacky
% draw gluon vertex
\global\advance\loopmidy by \Xone
\global\stemlength=400 % lengthen the stem since this is drawn in BOLD
\stemvertex1\drawvertex\gluon[\S 3](\loopmidx,\loopmidy)[3]
% Determine diameter and centre of fermion loop
\negate\Xtwo
\global\advance\Xtwo by \loopfrontx
\global\Xthree=\Xtwo % Store. Will use shortly
\double\Xtwo % \Xtwo is now the diameter of the fermion loop
\put(\loopfrontx,\Ytwo){\circle{\Xtwo}}
% Lastly the photon
% This begins located at root 1/2 times radius in x & y direction from centre
\multroothalf\Xthree % This is why we stored it.
\global\advance\loopfrontx by \Xthree
\global\advance\Ytwo by \Xthree
\drawline\photon[\NE\FLIPPED](\loopfrontx,\Ytwo)[5]
\end{picture}
In phantom mode we draw a `central loop' (extent=`0'). This gives us the
position of the east-most point of a complete loop and thus the true loop
``radius''. By symmetry we now use this to find the south-most position on an
incomplete loop (extent of seven).
We store the (negative of the)
``radius'' under the name \Xone and then draw the gluon
loop, clockwise, storing the endpoints as (\Xtwo,\Ytwo). We next draw
the three-gluon vertex beginning at the bottom of the gluon loop. To find this
point we subtract the radius (Xone) from the midpoint of the loop,
(loopmidx,loopmidy).
Next we draw the fermion loop.
We accomplish this by finding the radius of the circle, which is the difference
between the initial and final x (or y) coordinates of the gluon loop.
This is now stored as \Xthree. The centre is simply at the x
coordinate of the front of the gluon loop and the y coordinate of the rear.
Finally we use multroothalf in order to find the spot, 45o around the
circle, from which to draw the photon.