If (previously in a script) pen is already set down and then the glide block is run, it should sense if the pen is down and in this case set it up as shown in the screenshot above, then set it down again.
That's what I meant in the first place, but you're right that I haven't explained myself clearly enough.
No, it's an error in the glide library. The destination coordinates are established by a forth-and-back move. It's quite obvious that the pen should not draw in that phase and be restored to its previous state.
Execute this script to see the problem (with long duration)
I believe some introductions are in order! I am the newest member of the Snap! team through a partnership with SAP. I have been working with the UC Berkeley Snap course (Beauty and Joy of Computing) since 2018 as a Graduate Student Instructor. Looking forward to engaging with the forum community!
Thanks! And thanks to SAP, who's paying for their time. (Strange SAP politics; for some reason beyond me, this is easy to pay for, but cloud support, which they promised, in a contract with Berkeley, to pay for, they haven't found a way to get past their bean counters yet.)
I'm unsure if it belongs in a library but it is a style I prefer because this kind of thing comes up often enough to warrant an abstraction. I like the SICP version though it does require more sophistication for someone to understand how run with pen up action works.