Re: [platform-swt-dev] GC operations outside paint callback

[Silenio Quarti <Silenio_Quarti@xxxxxxxxxx>]

Yes, it is possible to draw outside of paint.




Stef van Dijk <svandijk@xxxxxxxxxx> 
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07/24/2004 09:49 AM
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Personal Profile and Personal Configuration (ie AWT) based on SWT also 
relies on this behavior. That's because in AWT you're allowed to get a 
Graphics at any time, draw with it at any time and hold the Graphics 
object for the entire life span of your application if you wish. Not that 
I think that's a particularly good choice on the part of AWT, but it is 
the way it's spec'ed. 

     Stef 



Knut Radloff/Raleigh/IBM@IBMUS 
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07/23/2004 04:27 PM 

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So if draw2d relies on it, it is probably expected to work by the users of 
SWT. I'd still like to hear from the SWT team "yes, this is in fact a 
supported way of using a GC" or "no". I'm thinking the answer is yes for 
SWT but don't want to make assumptions since in other toolkits the answer 
is no. 


Randy Hudson/Raleigh/IBM@IBMUS 
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07/23/2004 04:20 PM 

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This works fine.  This is how draw2d paints.  The only known issues are on 
GTK if you ARE inside a paint callback, and you try to create your own GC 
with a bigger clip region than the one sent in the paint event, painting 
will still be clipped to the region sent in the event.  The workaround is 
to use the repaint mechanism always or at least when this occurs. 

-Randy 


Knut Radloff/Raleigh/IBM@IBMUS 
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Is it valid for an application to render directly on a GC, outside a paint 
callback? E.g., given the code below am I guaranteed to get the expected 
line on all SWT implementations? I don't think this is spec'd anywhere. Is 
this "implementation dependent" behavior? 

shell = new Shell() 
shell.open() 
gc = new GC(shell); 
gc.drawLine(0, 0, 10, 0); 

The JUnit tests don't call GC operations inside a paint callback but they 
also don't test if a call actually rendered the expected output. 

Thanks, Knut