[Xy-pic] Problem with larger dots

[Michael Barr]

The dir {.} produces dots that are too small and too close together.  I 
have been trying for a while to get better ones.  Appended is my latest 
attempt.  If I adjust the parameters to make the horizontal and vertical 
look reasonable (although still not entirely satisfactory) the diagonal 
ones are completely off.  I have looked at the source code, but cannot 
figure out how the dots are generated and how to change them.

Michael Barr

\documentclass[12pt]{article}
\usepackage[arrow]{xy}
  \setbox0=\hbox{$A$}% Does nothing except load the font.
  \newdimen\axis \axis=\fontdimen22\textfont2%
  \newbox\bullbox \setbox\bullbox=\hbox{.}
  \wd\bullbox 0pt
  \ht\bullbox 2.0pt
  \dp\bullbox 1.0pt

  \def\bull{\kern 1.9pt \usebox\bullbox\kern 1.1pt}
\newdir{..}{\object{\bull}}
\begin{document}

$$\xy
  \POS(0,0)*+!!<0ex,\axis>{A}\ar@{..>}(25,0)*+!!<0ex,\axis>{B}
  \POS(0,0)*+!!<0ex,\axis>{A}\ar@{..>}(0,-25)*+!!<0ex,\axis>{D}
  \POS(0,0)*+!!<0ex,\axis>{A}\ar@{..>}(25,-25)*+!!<0ex,\axis>{C}
   \endxy$$