Central Loops

As can be seen from the previous example, loopfrontx,y and loopbackx,y are not at the same level as loopmidx,y or each other. This is because the peculiar way in which LATEX draws gluons. The result is that certain loops may appear stilted, for instance the gluon loop correction to a gluon propagator. To alleviate this problem an alternate mode exists. If the user requests that the number of `eighths' drawn be zero then a complete loop will be drawn in the central mode. In this mode the only parameters to be entered are the co-ordinates of the centre of the loop. The initial direction may be specified as anything and is irrelevant. ONLY complete loops may be drawn in this fashion. The returned parameters are the same but have slightly altered interpretations. loopmidx,y are as before. loopfrontx,y refer to the left-most point (that furthest west) of the loop and loopbackx,y refers to the right-most point (furthest east). For instance 

\drawloop\gluon[\NE 0](0,0)
would produce a complete loop centred at (0,0) with loopfronty and loopbacky both equal to zero. In this way one could produce
\begin{picture}(18000,8000) \drawloop\gluon[\NE 0](8000,0) \frontstemmed\drawlin... ...mmed\drawline\gluon[\W\FLIPPEDCENTRAL](\loopfrontx,\loopfronty)[5] \end{picture}

with the three statements 

\drawloop\gluon[\NE 0](0,0)
\frontstemmed\drawline\gluon[\E\CENTRAL](\loopbackx,\loopbacky)[5]
\frontstemmed\drawline\gluon[\W\FLIPPEDCENTRAL](\loopfrontx,\loopfronty)[5]