Improve HPGL pen change logic

[ithinkido]

It looks like you are calling a return to park position before each pen change. That is not a bad thing, but it is a bit of a strange way of doing it as the park position is the one that we set up in the config file, and it is not by default the point closest to the pen changer. Can I suggest that you only call move to park position before putting away the last pen, that is the SP0; command? For all other pen changes, simply put a PU; command before the pen change is called. This will mean that after the pen change the plotter will resume the last pen state before the change and that would be PU; It would still do an auto PU move before the pen change, even if you did not call it, but it would also then move to the last position before the pen change and try to first resume the last pen state (down) and leave a single dot with the new pen at the end of the old line before going to the new position.

[abey79]

@ithinkido What would be the right thing to do? My understanding is that the pen with go back to its previous position after a SP; command, so if I don't generate a homing command, it will go back to the end of the previous colour line. If the homing position is far from the pen carousel, both behaviours are weird/not very nice. However, if the homing position is near the carousel, the current behaviour is better. Do you have an idea on how to best deal with that?

[ithinkido]

I would just use PU; without co ordinates.

At the end of a layer when you call PU,SP.. it will automatically take the shortest path back to the pen changer. Once it has collected the pen it will travel back to the last position it was at before the pen change. This may or may not line up with start point of the next layer, but more that likely it will be close.

By using the define park position before a pen change you a grranteed to roll the paper out af far as possible, and at worst case, also drive the pen to the furthest point away from the pen carousel. The only possible bonus is if you get lucky you will drive the pen near the carousel, but you have still rolled the paper all the way out.

[abey79]

I agree that for rolling-paper-type plotter, PU is the best approach.

[ithinkido]

For a flatbed, park position will should (it is user defined , so it could be set anywhere) always be far away.