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From thomas.dewe...@kodak.com
Subject RE: Drag and drop breaks with a JSVGScrollPane?
Date Fri, 02 Dec 2005 13:26:15 GMT
Hi Michael,

"Bishop, Michael W. CONTR J9C880" <Michael.Bishop@je.jfcom.mil> wrote on 
12/02/2005 08:09:40 AM:

> OK, you're right; adding a viewBox isn't terribly difficult.  Where do I 
get 
> the bounds for this viewBox?  It seems like it would change when I 
scroll the 
> canvas?  Is it the size of the document itself that I can ask the 
JSVGCanvas for?

   The viewBox should be the 'total extent' of the document.  It does not 
change
when you scroll the document.  It _might_ change when someone drags an 
object
'outside' of the current bounds of the document, this would be up to your
application (does the canvas have a fixed extent or does it grow and 
shrink
as people drag things around).

   You could ask the root SVG element for it's BBox if you want it to be
dynamic but you need to do it in the update manger thread.  For example
you might want to query the bbox at the end of a drag operation and
update the viewbox if it has changed.  Be careful however as changing
the width/height of the viewBox will cause the entire graphics tree to
be rebuilt (to properly update properties/attributes that use '%').

> ________________________________
> 
> From: thomas.deweese@kodak.com [mailto:thomas.deweese@kodak.com]
> Sent: Fri 12/2/2005 6:02 AM
> To: batik-users@xmlgraphics.apache.org
> Subject: Re: Drag and drop breaks with a JSVGScrollPane?
> 
> 
> 
> Hi Michael,
> 
> "Bishop, Michael W. CONTR J9C880" <Michael.Bishop@je.jfcom.mil> wrote on
> 12/01/2005 10:58:07 AM:
> 
> > I added a JSVGScrollPane around my JSVGCanvas.  Now I'm getting random
> NPEs
> > when dragging an element around the canvas.  This looks 
thread-related,
> but my
> > drag and drop code hasn't changed.  I'm updating the document in the
> > JSVGCanvas's UpdateManager with a Runnable.  Here's the stack trace:
> 
>    This looks like a bug in the JSVGScrollPane (it's looking at GVT 
stuff
> outside of the update manager thread).  The fix is pretty simple 
however,
> add a viewBox attribute to the root SVG element.  This is a good idea
> anyways.
> 
>    The problem is that if there is no viewbox the canvas tries to be
> nice and look at the actual bounds of the GraphicsNode and use that
> instead.  The problem is that unless it does that in the UpdateManager
> thread your code could have invalidated the bounds information at the
> same time - in which case it just returns a null BBox.
> 
>    Probably the 'right' thing to do is for the canvas to 'cache' the
> bounds of the GVT tree for each rendering/update - then the scroll pane
> can just get that.  I get nervous about adding invokeAndWait calls
> in the ScrollPane as it may cause lots of people to have lock ups.
> 
> > Is there something else I need to manage when I have a JSVGScrollPane? 
I
> just
> > wanted to be able to scroll around the canvas when I'm zoomed in.  All 
I
> did
> > was wrap the JSVGCanvas in the JSVGScrollPane.  Oddly enough, this 
error
> 
> > occurs if I don't even add the JSVGScrollPane to the application.  As
> long as
> > I call its constructor with the JSVGCanvas as the parameter, the error
> happens.
> 
>    Yes, when the JSVGScrollPane is constructed it attaches it's self to
> the
> update callbacks of the canvas so it can keep the scrollbars in sync
> (really
> all the scroll pane does is offer visual feedback and manipulation of 
the
> existing scrolling support in the canvas).
> 
> 
> 
> [attachment "winmail.dat" deleted by Thomas E. DeWeese/449433/EKC] 
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