Rendering a dynamic SVG document to an offscreen buffer
It can be helpful in some circumstance to render a Dynamic SVG document not to the screen but to an offscreen buffer. This is most useful when you have a large SVG Document that you want to output as JPEG or PNG with a few minor variations from rendering to rendering.
By treating the "template" document as a dynamic document where you just modify small pieces you can avoid the overhead of rereading and parsing the SVG, as well as the building of the Rendering tree from that SVG document (which involves parsing many attributes, performing CSS cascade etc.
The following example takes the filename on the command line of a 'base' document to read, it then creates a 'dynamic' rect on top of the document and renders the document with the rect moving across the top of the document. It renders the images to a BufferedImage which it then writes to a sequence of PNG files.
Example
package org.example;
import java.awt.geom.AffineTransform;
import java.awt.Rectangle;
import java.io.File;
import java.io.OutputStream;
import java.io.IOException;
import java.io.FileOutputStream;
import java.net.MalformedURLException;
import java.util.List;
import org.apache.batik.ext.awt.image.codec.png.PNGEncodeParam;
import org.apache.batik.ext.awt.image.codec.png.PNGImageEncoder;
import org.apache.batik.dom.svg.SAXSVGDocumentFactory;
import org.apache.batik.bridge.BridgeContext;
import org.apache.batik.bridge.BridgeException;
import org.apache.batik.bridge.GVTBuilder;
import org.apache.batik.bridge.UpdateManager;
import org.apache.batik.bridge.UpdateManagerAdapter;
import org.apache.batik.bridge.UpdateManagerEvent;
import org.apache.batik.bridge.UserAgentAdapter;
import org.apache.batik.util.RunnableQueue;
import org.apache.batik.util.XMLResourceDescriptor;
import org.apache.batik.gvt.CanvasGraphicsNode;
import org.apache.batik.gvt.CompositeGraphicsNode;
import org.apache.batik.gvt.GraphicsNode;
import org.apache.batik.gvt.renderer.ConcreteImageRendererFactory;
import org.apache.batik.gvt.renderer.ImageRenderer;
import org.apache.batik.gvt.renderer.ImageRendererFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
public class TestOffScreenRender {
static final String SVGNS = "http://www.w3.org/2000/svg";
Document document;
UserAgentAdapter userAgent;
GVTBuilder builder;
BridgeContext ctx;
ImageRenderer renderer;
AffineTransform curTxf;
UpdateManager manager;
GraphicsNode gvtRoot;
int DISPLAY_WIDTH = 1280;
int DISPLAY_HEIGHT = 1024;
public TestOffScreenRender (Document doc) {
userAgent = new UserAgentAdapter();
ctx = new BridgeContext(userAgent);
builder = new GVTBuilder();
document = doc;
}
public void init() {
GraphicsNode gvtRoot = null ;
try {
ctx.setDynamicState(BridgeContext.DYNAMIC);
gvtRoot = builder.build(ctx, document);
}
catch (BridgeException e) {
e.printStackTrace();
System.exit(1);
}
ImageRendererFactory rendererFactory;
rendererFactory = new ConcreteImageRendererFactory();
renderer = rendererFactory.createDynamicImageRenderer();
renderer.setDoubleBuffered(false);
float docWidth = (float) ctx.getDocumentSize().getWidth();
float docHeight = (float) ctx.getDocumentSize().getHeight();
float xscale = DISPLAY_WIDTH/docWidth;
float yscale = DISPLAY_HEIGHT/docHeight;
float scale = Math.min(xscale, yscale);
AffineTransform px = AffineTransform.getScaleInstance(scale, scale);
double tx = -0 + (DISPLAY_WIDTH/scale - docWidth)/2;
double ty = -0 + (DISPLAY_WIDTH/scale - docHeight)/2;
px.translate(tx, ty);
CanvasGraphicsNode cgn = getGraphicsNode(gvtRoot);
if (cgn != null) {
cgn.setViewingTransform(px);
curTxf = new AffineTransform();
} else {
curTxf = px;
}
manager = new UpdateManager(ctx, gvtRoot, document);
// 'setMinRepaintTime' was added to SVN. This isn't
// essential but prevents 'frame skipping' (useful
// for "recording" content, not needed for live display).
manager.setMinRepaintTime(-1);
try {
manager.dispatchSVGLoadEvent();
} catch (InterruptedException ie) {
ie.printStackTrace();
}
renderer.updateOffScreen(DISPLAY_WIDTH, DISPLAY_HEIGHT);
renderer.setTree(gvtRoot);
renderer.setTransform(curTxf);
renderer.clearOffScreen();
renderer.repaint(new Rectangle(0, 0, DISPLAY_WIDTH, DISPLAY_HEIGHT));
manager.addUpdateManagerListener(new UpdateManagerAdapter() {
public void updateCompleted(UpdateManagerEvent e) {
render(e.getImage());
}
public void managerSuspended(UpdateManagerEvent e) {
// Make sure pending updates are completed.
System.exit(0);
}
});
manager.manageUpdates(renderer);
this.gvtRoot = gvtRoot;
}
private CanvasGraphicsNode getGraphicsNode(GraphicsNode gn) {
if (!(gn instanceof CompositeGraphicsNode))
return null;
CompositeGraphicsNode cgn = (CompositeGraphicsNode) gn;
List children = cgn.getChildren();
if(children.size() == 0)
return null;
gn = (GraphicsNode) children.get(0);
if (!(gn instanceof CanvasGraphicsNode))
return null;
return (CanvasGraphicsNode) gn;
}
int imgCount = 1;
public void render(java.awt.image.BufferedImage img) {
// paint the image or stream the image to the client display
try {
String file = "frame."+(imgCount++)+".png";
System.err.println("Output: " + file);
OutputStream os = new FileOutputStream(file);
PNGEncodeParam params = PNGEncodeParam.getDefaultEncodeParam(img);
PNGImageEncoder pngEncoder = new PNGImageEncoder(os, params);
pngEncoder.encode(img);
os.flush();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
/**
* @param args
*/
public static void main(String[] args) {
if (args.length < 1) {
System.out.println("You must provide background SVG file");
System.exit(1);
}
String docStr = args[0];
String xmlParser = XMLResourceDescriptor.getXMLParserClassName();
SAXSVGDocumentFactory df;
df = new SAXSVGDocumentFactory(xmlParser);
Document doc = null;
TestOffScreenRender render = null;
Element r=null;
try {
File f = new File(docStr);
doc = df.createSVGDocument(f.toURL().toString());
r = doc.createElementNS(SVGNS, "rect");
r.setAttributeNS(null, "x", "100");
r.setAttributeNS(null, "y", "200");
r.setAttributeNS(null, "width", "200");
r.setAttributeNS(null, "height", "150");
r.setAttributeNS(null, "fill", "crimson");
r.setAttributeNS(null, "stroke", "gold");
r.setAttributeNS(null, "stroke-width", "3");
doc.getDocumentElement().appendChild(r);
render = new TestOffScreenRender(doc);
render.init();
} catch (IOException ioe) {
ioe.printStackTrace();
System.exit(0);
}
final Element rect = r;
RunnableQueue rq = render.manager.getUpdateRunnableQueue();
for (int i=1; i<10; i++) {
final int x = 100+ (i*10);
try {
rq.invokeAndWait(new Runnable() {
public void run() {
rect.setAttributeNS(null, "x", ""+x);
}
});
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}
render.manager.suspend();
}
}