Why is my printing so jagged?

[osiris@cs.utexas.edu (Rob Browning)]

I have a routine that graphs a line by "connecting the dots" using a
#_MoveTo and #_LineTo for each segment.  While this looks fine on screen,
when I print it to a laserwriter (using print-u.lisp and letting the driver
handle Quickdraw->PostScript translation) it looks ugly.  The line is very
lumpy even though I know that the endpoints of adjacent segments are on top
of one other.

Why is this, and is there a straghtforward fix?

I want to remain as print driver independent as possible because this
program needs to be able to print to laser printers, inkjets and most
importantly, Calcomp plotters.

(An aside: I was looking through the info in IM:Imaging and I was stunned
by how poorly abstracted the printing vs screen drawing issues were.  I
couldn't believe that you have to write driver specific code for something
as simple as a thin line.  Why wouldn't there be a standard call for this
such that the screen or the print driver (speaking whatever language to the
printer) approximates it as best it can?)

Thanks,

--Rob.