Horizontal dotted lines using PLOTS

["Oliver Smith" <osmith(at)dera.gov.uk>]

Okay maybe I'm being too much of a perfectionist but this is really
annoying.

I use dotted lines to box an area of interest, line width is two pixels. A
solid white line is first plotted then a dotted black line plotted on top of
the first. A vertical line drawn this way looks great, but a horizontal line
is not so good; the dots that make up the black line are not square, but 'L'
shaped.

for 0 = white pixel
for # = black pixel

Vertical line:

00
00
##
##
00
00
00
00
##
##
00
00

Horizontal line:

000#00000#00
00##0000##00


Demonstrable by:

IDL Version 5.3.1 (Win32 x86). (c) 2000, Research Systems, Inc.

IDL> plot, findgen(100)
IDL> plots, [20,20], [10,80], linestyle = 0, color = 255, thick = 2, /data
IDL> plots, [20,20], [10,80], linestyle = 1, color = 0, thick = 2, /data
IDL> plots, [20,80], [10,10], linestyle = 0, color = 255, thick = 2, /data
IDL> plots, [20,80], [10,10], linestyle = 1, color = 0, thick = 2, /data

The horizontal line ends up looking very poorly defined if it is drawn on
top of a relatively light coloured background.

So can anyone reproduce this, and can anyone come up with a work-around
without changing the thickness of the lines?

Thanks,

Oliver Smith