I see a draw_lines_testing in backend_ps. I think it could
> be a good approach, but it doesnt make it very easy to
> skip unplottable elements like nans, infs. Could xy_tup
> accept a kwarg to make it raise an error when it tries to
> transform an inf or a nan?
I don't see why not. Alternatively, the nan testing could be done in
"drawone". I was planning on filtering the path in chunks (eg 100
verts at a time) through drawone using map or listcomps, which should
be faster and will not violate the max path size of some postscript
interpreters. But I didn't get that far when my wife made me go to
bed. So if you want to pick up where I left off, feel free.