Yes, you are right and I understood that.
Anyway, I started another project, but I don't see how I could draw lines with arrows at the ends. There is no LineStartCap, LineEndCap, etc. like in C#.
Here is my project:
Drawing1.aia (510.9 KB)
You could start by initializing global variables to 0 .
Empty sockets are an error.
Also, read the chapter on procedures in
http://www.appinventor.org/book2
particularly the part about procedure parameters.
Maybe this can be useful to you:
If we wanted arrows at both ends of the line, both pointing away <--->
?
Do one arrow pointing in the opposite point order to the first order, so one overlaps the other.