Save a Processing sketch to a PNG file, server-side with no GUI/display

Question

I'd like to use Processing to render a visualization on the server side (headlessly, with no GUI). The Processing sketch is static (i.e. does not animate), so I only need to grab the first frame, and I'd like to serve this result out to the users of our web application on-demand.

I've searched around a bit on the processing.org forums and it's been suggested that Processing is not intended to be launched headlessly. The only hack I've seen to do it is one involving launching a headless X11 display:

Xvfb :2 &
export DISPLAY=":2"
./myapp
killall -9 Xvfb

.. Which is not going to work for us as we'd like to have a pure-Java solution and can't always guarantee an X renderer on the server-side.

How do I do this in pure Java?

Answer 1

Xvfb is likely to be faster than a java renderer, and a hardware-accelerated X server will be the fastest by a large margin, but if you want a 'pure' java solution you could try the Pure Java AWT Toolkit.

EDIT: Here's a boot command line example lifted from here:

java -Xbootclasspath:JDK/jre/lib/rt.jar:LIB/pja.jar -Dawt.toolkit=com.eteks.awt.PJAToolkit -Djava.awt.graphicsenv=com.eteks.java2d.PJAGraphicsEnvironment -Djava.awt.fonts=JDK/jre/lib/fonts mainclassname args

Answer 2

Create a standard headless Java app, create a PGraphics object in it(1) and perform all of your drawing operations on that. Then save the PGraphics object to disk as an image file using .save().

1 You may need to obtain this from a PApplet, I'm not sure if you can create it directly.

The code will look mode or less like this:

PApplet applet = new PApplet();
PGraphics g = applet.createGraphics(200, 400, PApplet.JAVA2D) // same params as size()
g.beginDraw();
g.ellipse // ... etc, your drawing goes here
g.endDraw();
g.save("filename.png");