[plt-scheme] Yet another question. And this time: animations

I actually used on-paint, not refresh, but I had to clear the canvas 
before redrawing - otherwise it would leave a trail behind...
What's wrong with calling on-paint from other threads though? That's 
what I did...
Anyway, I have a new problem with double buffering:
(define bmp (make-object bitmap% 10000 10000 #f))
(define bmp-dc (instantiate bitmap-dc% () (bitmap bmp)))
--> Unused instantiation variable error (or something like that, don't 
remember ran it from a computer at the uni this morning...)
Why is that?

Katsmall the Wise
kela_bit at netvision.net.il

Matthew Flatt wrote:

>I think another problem is that `refresh' clears the canvas before it
>calls `on-paint'. I'll will add a flag in the near future to disable
>the clear.
>
>Meanwhile, you can call `on-paint' directly if you're running in the
>handler thread.
>
>Matthew
>
>At Sun, 2 Mar 2003 16:36:59 -0600, Robert Bruce Findler wrote:
>  
>
>>You can use offscreen bitmaps. Put the next frame of the animation into
>>a bitmap and then just draw that into the canvas.
>>
>>Robby
>>
>>At Mon, 03 Mar 2003 00:08:51 +0200, Katsmall the Wise wrote:
>>    
>>
>>>  For list-related administrative tasks:
>>>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>>>
>>>Hello again,
>>>
>>>Now that I have normal drawings settled, what about some animations? Are 
>>>they possible?
>>>I tried making moving parts via boxes which are set every 0.1 secs and 
>>>then refresh the canvas, yet (quite logically) the screen blinks like 
>>>that...
>>>Is there a built-in way to make animations?
>>>
>>>Katsmall the Wise
>>>kela_bit at netvision.net.il
>>>
>>>
>>>      
>>>
>
>
>  
>