> As to detatchAll() versus a specific portrayal: laziness.  It's easy  

> for us to clean out everything, but detatching a specific portrayal  

> means shifting a bunch of stuff down.  We figured one could detach  

> everything and then reattach the stuff you wanted.  :-)  :-) 



I tried that first, but the Portrayals' visible flags are package-private to

sim.display. So it isn't possible to know which Portrayals should be visible

when they are reattached (from outside the sim.display, anyway). No big deal

though, if I decide I really need that ability I'll just hack the Display2D

directly. 



Regarding the immutability stuff: Increasing the heap size dramatically

improves performance when the immutable field flag is set to true. So it all

makes sense now :) I guess I should've tried that first.



Thanks for your help!



-Marc