GraphicsDeviceTest.java

package org.renjin;

import org.renjin.script.RenjinScriptEngine;

import javax.script.ScriptException;

public class GraphicsDeviceTest {

  public static void main(String[] args) throws ScriptException {

    // Initialize the engine
    RenjinScriptEngine engine = new RenjinScriptEngine();
    engine.eval(".mydevice <- function() grDevices:::JavaGD(deviceClass = 'org.renjin.MyDevice')");
    engine.eval("options(device=.mydevice)");

    // Run R code that generates the plots
    engine.eval("plot(1:12)");
    engine.eval("plot(1:24)");

    // Shutdown the Graphics device. this will flush the last active plot
    engine.eval("graphics.off()");

  }
}

MyDevice.java

package org.renjin;

import org.renjin.eval.Session;
import org.renjin.grDevices.GDContainer;
import org.renjin.grDevices.GDObject;
import org.renjin.grDevices.GDState;
import org.renjin.grDevices.GraphicsDevice;
import org.renjin.sexp.ListVector;

import java.awt.*;
import java.awt.image.BufferedImage;

public class MyDevice extends GraphicsDevice {

  private final Session session;
  private final ListVector deviceOptions;

  public MyDevice(Session session, ListVector deviceOptions) {
    this.session = session;
    this.deviceOptions = deviceOptions;
  }

  @Override
  public void open(double width, double height) {

    BufferedImage bufferedImage = new BufferedImage((int)width, (int)height, BufferedImage.TYPE_INT_ARGB);
    Dimension size = new Dimension((int)width, (int)height);

    Graphics2D graphics = bufferedImage.createGraphics();
    graphics.setBackground(Color.WHITE);
    graphics.clearRect(0, 0, (int)size.getWidth(), (int)size.getHeight());

    GDState state = new GDState();

    container = new GDContainer() {

      private int deviceNumber;
      private boolean empty = true;

      @Override
      public void add(GDObject o) {
        empty = false;
        o.paint(null, state, graphics);
      }

      @Override
      public void reset() {
        if(!empty) {
          flush();
        }
        graphics.setClip(null);
        graphics.clearRect(0, 0, (int) size.getWidth(), (int) size.getHeight());
      }

      @Override
      public GDState getGState() {
        return state;
      }

      @Override
      public Graphics getGraphics() {
        return graphics;
      }

      @Override
      public void syncDisplay(boolean finish) {
        // No action: we do not have a display
      }

      @Override
      public void setDeviceNumber(int dn) {
        this.deviceNumber = dn;
      }

      @Override
      public void closeDisplay() {
        flush();
      }

      @Override
      public int getDeviceNumber() {
        return deviceNumber;
      }

      @Override
      public Dimension getSize() {
        return size;
      }

      private void flush() {
        System.out.println("New plot!");
        // At this point you can do something with BufferedImage.
        // For example, write it to a byte[] array that can be sent to the client
        // when the request is complete.
      }
    };
  }
}