SVG interaction in python with cairo, opengl and rsvg

Question

I render a huge SVG file with a lot of elements with Cairo, OpenGL and rsvg. I draw svg on cairo surface via rsvg and create an OpenGL texture to draw it. Everything is fine. And now I have to interact with elements from SVG. For example, I want to guess an element by coordinates. And I want to change the background of some path in SVG. In the case of changing background I think, I can change SVG DOM and somehow re-render a part of SVG. But in the case of hit testing elements I'm totally embarrassed.

So, is there some python library to interact with SVG? Is it possible to stay with cairo and rsvg and how can I implement it myself? Or is there a better way to render SVG in OpenGL and interact with it in python? All I want is load SVG, manipulate its DOM and render it

Answer 1

I don't know much about librsvg, but it does not appear to have been updated since 2005, and so I would be inclined to recommend using a different implementation.

If you don't have dependencies on any Python libraries outside of the standard library, then you could use Jython together with Batik. This allows you to add event handlers, as well as change the DOM after rendering.

For an example of how to do this with Java, see this link.

Here's a quick port to Jython 2.2.1 (runs, but not thoroughly tested):

from java.awt.event import WindowAdapter;
from java.awt.event import WindowEvent;

from javax.swing import JFrame;

from org.apache.batik.swing import JSVGCanvas;
from org.apache.batik.swing.svg import SVGLoadEventDispatcherAdapter;
from org.apache.batik.swing.svg import SVGLoadEventDispatcherEvent;
from org.apache.batik.script import Window;

from org.w3c.dom import Document;
from org.w3c.dom import Element;
from org.w3c.dom.events import Event;
from org.w3c.dom.events import EventListener;
from org.w3c.dom.events import EventTarget;

class SVGApplication :

    def __init__(self) :

        class MySVGLoadEventDispatcherAdapter(SVGLoadEventDispatcherAdapter):
            def svgLoadEventDispatcherListener(e):
                # At this time the document is available...
                self.document = self.canvas.getSVGDocument();
                # ...and the window object too.
                self.window = self.canvas.getUpdateManager().getScriptingEnvironment().createWindow();
                # Registers the listeners on the document
                # just before the SVGLoad event is
                # dispatched.
                registerListeners();
                # It is time to pack the frame.
                self.frame.pack();

        def windowAdapter(e): 
            # The canvas is ready to load the base document
            # now, from the AWT thread.
            self.canvas.setURI("doc.svg");

        self.frame = JFrame(windowOpened = windowAdapter, size=(800, 600));

        self.canvas = JSVGCanvas();
        # Forces the canvas to always be dynamic even if the current
        # document does not contain scripting or animation.
        self.canvas.setDocumentState(JSVGCanvas.ALWAYS_DYNAMIC);
        self.canvas.addSVGLoadEventDispatcherListener(MySVGLoadEventDispatcherAdapter()) ;

        self.frame.getContentPane().add(self.canvas);

        self.frame.show()

    def registerListeners(self) :
        # Gets an element from the loaded document.
        elt = self.document.getElementById("elt-id");
        t = elt;

        def eventHandler(e):
            print e, type(e)

            self.window.setTimeout(500,run = lambda : self.window.alert("Delayed Action invoked!"));
            #window.setInterval(Animation(), 50);

        # Adds a 'onload' listener
        t.addEventListener("SVGLoad", false, handleEvent = eventHandler );

        # Adds a 'onclick' listener
        t.addEventListener("click", false, handleEvent = eventHandler );



if __name__ == "__main__":
    SVGApplication();

Run with:

jython -Dpython.path=/usr/share/java/batik-all.jar:/home/jacob/apps/batik-1.7/lib/xml-apis-ext.jar test.py

Answer 2

An alternative approach would be is to use blender. It supports svg import and interaction using python. I don't think it will allow you to edit the dom after import.

Answer 3

I had to do the same (changing element color for instance), and had to modify rsvg library because all those nice features exist but they are hidden. You have to make a new interface to link to the nice features.