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From thomas.dewe...@kodak.com
Subject Re: Canvas not updating properly
Date Thu, 01 Jun 2006 09:45:03 GMT
Hi Philip,

"philip zuniga" <philip.zuniga@gmail.com> wrote on 06/01/2006 12:24:22 AM:

> I am currently working on an SWT application that is embedded with a 
> canvas. I based my work on some source codes that were posted in this 
> lists. In the application, the canvas is translated every time I move 
> scroll. The translation is done via the rendering transform of the 
> (just like the same way as JSVG Scrollpane works).

    Actually the JSVGScrollpane updates the painting transform while you
are scrolling and only updates the rendering transform when you finish
the scroll operation.

> The process seems to be logical. But when I run it and move the scroll, 
> there are some times (especially when I move the scroll quickly) when 
> the canvas does not update properly, and instead it just stays to its 
> current position. But, if I move the window of the application in a 
> place where the canvas is hidden and show it up again, then the canvas 
> would be updated. Or, if i place the window of another application over 
> the canvas,and remove it, then the canvas gets updated. 
> do you know where the problem is?

   It sounds like you are loosing one or more of the 'internally' 
repaint events from the Canvas.  When you update the rendering transform
the rendering of the Canvas is actually done in a separate thread to
avoid 'locking up' the main UI thread.  When the rendering is completed
it notifies the canvas which grabs the updated image to display (which
seems to be working fine since if you manually generate an 'update' 
event it redraws correctly).  It then triggers a repaint of the canvas
this part seems to be the problem part.

   This is made a bit more complex by the fact that triggering many
redraws quickly usually causes the earlier redraws to be canceled.
I'm fairly sure that this is working in an AWT/Swing only world.

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