Broken Line using DrawLine screen command

1
I am running an experiment that presents line segments of
various orientations using the DrawLine command.
Unfortunately, for some orientations (angles) the lines appear
choppy or broken. Given that my experiment is a discrimination
experiment requiring subjects make a judgement only the basis
of orientation, the way the two lines differ in the way they are
broken can serve as a salient and unwanted cue. Does anyone
know how to get relatively straigth lines with this command. So
far, I have tried changing the screen resolution with no apparent
advantage.

Thanks,

CK