the other ones are good ideas, the hard part is to push it all in to an already pretty space limited mobile UX
hmmm.... maybe if i push the colored dots at the bottom to the side and then add a dropdown for line there ... or next to the erased / draw button
i could make the erase draw button a dropdown for line types, though ...
A quibble: Choosing between Draw|Erase|Toggle is awkward on mobile (Safari on iPhone). The old toggle between Draw|Erase was quick but the new pulldown list widget is in the upper left while the choices always pop open at the bottom of the screen.
Perhaps move the pulldown list to the bottom on mobile or make it two toggle buttons (Mode: Draw|Erase, Line type: Bounce|Toggle)?
Some enhancement ideas:
Add a mark where the dots drop from and perhaps a faint line to show the drop path.
Add an edit mode so existing lines could be selected then either erased, moved, lengthened, shortened, or have their type changed between Bounce|Toggle. Going further allow a point to be selected and move it or rotate a line around it.
A line that toggles on/off when a ball passes through it or collides with it would also be fantastic.
Also a trampoline line/shock absorber line(s).
The default/starting line should be a diagonal too, since it makes it more clear what is happening and you don't get that decaying bouncing thing.
very cool idea