Re: Simple bitmap question

[Robert Bruce Findler <robby@cs.rice.edu>]

When things are drawn and erased is a platform-specific mystery that
the on-paint abstraction is designed for. Macos, windows and X all
decide when things need to be redrawn and they notify your program by
triggering a callback that eventually calls your on-paint method. If
you don't override the on-paint method, you miss some of these
callbacks. I'm not sure exactly which you were missing some in this
particular program -- it depends on what platform you were on, how the
windows appeared, (which window manager you're using) etc etc.

Long story short: use on-paint :)

Robby