I would like to select points on my curve by dragging a square with the mouse. Of course, I can build it myself, but I was wondering, is it easier to do this?
Unfortunately not. You have to do it yourself. ZG does not provide more complex tools for interaction.
You will probably need to subscribe to " mouse down " and " mouse up ", reverse convert the points found, and then find all the points in the range (i.e. by searching inside the Points Collection of your curve (s)).
Just remember that the default action you described is related to scaling the line width, and you will have to disable it.