If I understand right, the dashes would have uniform length once projected to the x-axis, but not uniform length. For example a curve with a very steep section might appear to be plotted solid.
$xrule(t) and $yrule(t) could parametrize the curve by arc length. You might have to solve a calculus problem each time you do that, but if it's only four problems in APEX that are of concern here, that's more of a fun diversion than a tedious burden.