-----Original Message-----
From: Thomas DeWeese [mailto:[EMAIL PROTECTED]
Sent: Friday, September 09, 2005 6:38 AM
To: [email protected]
Subject: Re: Basic SVG management in Batik with white-boarding.
Hi Michael,
Bishop, Michael W. CONTR J9C880 wrote:
> I'm trying to develop a simple white-boarding style program with
> Batik and have run into a couple fundamental problems. Here is a
brief
> outline of the steps used:
>
> - User draws a shape or line on the application's glass
pane.
>
> - X and Y coordinates are saved and then drawn to an
> SVGDocument via SVGGraphics2D object.
>
> - SVGCanvas "sets" the SVGDocument and the resulting changes
> are shown on the screen.
>> You should probably just append the new SVG object to the current
>> document. If you tell Batik to treat the document as ALWAYS_DYNAMIC
>> and do the append in the UpdateManager's RunnableQueue (just search
>> the list for these things for examples) Batik will much more
efficiently
>> update the display.
OK, I understand the thought process. Telling the JSVGCanvas to
treat the document as ALWAYS_DYNAMIC registers a bunch of listeners.
The UpdateManager can register threads that I should write to append to
the document. Unfortunately, there seems to be no way to "search" this
list; the link to "EyeSearch" on the main page is advertised as being
broken and well, it is...:) Am I missing something? It looks like I
need to do the following:
- Register a GVTTreeListener to know when the first rendering of the
canvas has occurred. This is necessary because the canvas'
UpdateManager is null.
- Create a new SVG element (perhaps with SVGGraphics2D?) based on the
user's drawing operation.
- Write a thread that appends data to the SVGDocument and invoke this
thread with the UpdateManager.
> Now this works fine until I try to "save" the results to an SVG
> file. The interaction with the document doesn't work as expected for
me.
>
> I have to do the following to get anything to render on the screen:
>
> Element root = svgDocument.getDocumentElement();
>
> svgGraphics2D.getRoot(root);
>
> Only when I make these calls, will anything show when I call
> svgCanvas.setDocument(svgDocument).
>> Yes, it's important to know that the SVGGraphics2D only
>> uses the document you give it as a 'factory' for elements.
>> It does not insert it's elements into the document.
Ok, the relationship between SVGGraphics2D and the document is what
I don't think I understand. I was under the impression that calls to
SVGGraphics2D updated the document it was created with. I create a
document like so:
String svgNamespaceURI = SVGDOMImplementation.SVG_NAMESPACE_URI;
DOMImplementation domImpl = SVGDOMImplementation.getDOMImplementation();
svgDocument = (SVGDocument) domImpl.createDocument(svgNamespaceURI,
"svg", null);
Then I do rendering using the SVGGraphics2D. How can I use the
SVGGraphics2D object to:
- Create a single "piece" that identifies a drawing operation complete
with pen color, shape type, size, etc. For example, here is a pinkish
oval I drew on my canvas:
<defs id="genericDefs" />
<g>
<g fill="rgb(255,102,102)" stroke="rgb(255,102,102)">
<ellipse rx="69" fill="none" ry="47.5" cx="174" cy="196.5" />
</g>
</g>
- Assign an "ID" to this piece so I can reference it later.
- Append it to the document that is used to maintain the state of the
canvas.
I know I could probably do basic shapes in SVG myself, but more advanced
functionality will need to come later and I'd like to do it in a
consistent manner. If I can use the SVGGraphics2D, I have a uniform way
of doing pretty much everything that Graphics2D can do with SVG
transformation.
> After doing that, displaying the resultant XML doesn't look correct.
> Here is output from a line, a box, and an oval:
> <!--Generated by the Batik Graphics2D SVG Generator-->
[...]
> <!--Generated by the Batik Graphics2D SVG Generator-->
[...]
> <!--Generated by the Batik Graphics2D SVG Generator-->
[...]
> <!--Generated by the Batik Graphics2D SVG Generator-->
> Again, I have to make the call to SVGGraphics2D.getRoot(...) to
display
> anything at all. I don't understand why I have separate definitions
and
> doubly-nested <g> elements for each shape. It also looks like the SVG
> generator is generating a different document fragment for every paint
> operation which may be what it's supposed to do.
>> This is exactly what it does. The real purpose of the
SVGGraphics2D
>> is to turn 'complex' drawing operations into SVG. For simple
primitives
>> you can do a much better job of creating the elements and making a
>> 'pretty' document.
So SVGGraphics2D on every draw/render operation will do:
<!--Generated by the Batik Graphics2D SVG Generator-->
<defs id="genericDefs" />
<g>
<g ...>
<.../>
</g>
</g>
> A related question is, how can I identify each object I draw? I've
seen
> in the SVG specs, an "id" can be given to a <g> element. In a later
> iteration, I may want to identify and "move" or "delete" a shape I've
> already drawn. Does the Batik toolkit allow me to give an ID to a
draw
> operation and manipulate it later, or will I have to dig through the
XML
> document myself to gain that functionality?
>> Well you can call getRoot without an SVG Element in which case
>> it will construct an SVG Element for you which you can add your
>> 'id' to - which isn't much mucking with the document.
Right, this seems like what I want to do as described above, but
again, I'm missing the relationship between the SVGDocument and the
SVGGraphics2D. Would I do something like this?
Element element = svgGraphics2D.getRoot();
// This line is pseudocode, so excuse syntax errors.
Element.setAttribute("id", "someId");
svgGraphics2D.drawLine(...);
and have the result be an SVG snippet with a line drawn and an ID set?
In short, when I draw, how do I know which element I'm working with?
The "getRoot()" call is what confuses me.
Michael Bishop
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