Question about flushing Display on Canvas

Lex Spoon lex at
Tue May 3 15:29:58 UTC 2005

> > It would be great if there were a way that was as easy to draw in
> > Morphic as Milan is seeking.  If you draw onto the Display directly,
> > Squeak is smart enough to flush things immediately as you draw.  It's
> > not fast, but it's easy to use and understand.  On the other hand, if
> > you play by Morphic's rules, then what can you do?
> Implement a drawOn: method ;-)

Yes, that's what people should eventually learn, but think way back to
before you were comfortable programming GUI's...   Many people have a
hard time thinking about this idea that a widget is passive and waits to
be asked to draw itself.  Many people would like to write code along the
lines of:

	1. compute a new point to draw.
	2. draw it.
	3. go to 1.

Or maybe:

	Whenever a building is destroyed, draw an explosion on top of it.


	Every 10 milliseconds, draw a new square at a random place.

These are awkward for a beginner in Squeak right now.  Before you can
implement them, you have to code up some extra infrastructure to manage
a form behind the scenes.

On further thought, though, there actually is a way to do this in Squeak
right now: using addMorph:.  Instead of drawing an ellipse, add an
EllipseMorph to the right location.  There are (or should be) morphs for
all of the canvas commands....


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