screengrab.java

import java.awt.*;
import java.awt.image.*;
import java.awt.event.KeyEvent;

Robot player;

BufferedImage capture = null;
PImage converted = null;

void setup() {
  size(400, 350);
  
  converted = new PImage(width, height, PConstants.ARGB);
  
  try {
    player = new Robot();
  } catch(Exception e) { println(e.toString()); }
}

void init() {
  // trick to make it possible to change the frame properties
  frame.removeNotify(); 
 
  // comment this out to not have the window "float"
  frame.setAlwaysOnTop(true); 
 
  frame.setResizable(true);  
  frame.addNotify();
  
  super.init();
}

void draw() {
  try {
    Point winloc = frame.getLocation();
    
    Rectangle screenRect = new Rectangle(winloc.x+frame.getWidth(), winloc.y, frame.getWidth(), frame.getHeight());
    capture = player.createScreenCapture(screenRect);
      
    capture.getRGB(0, 0, converted.width, converted.height, converted.pixels, 0, converted.width);
    converted.updatePixels();
    
    image(converted, 0, 0);
    
    rectMode(CENTER);
  } catch(Exception e) { println(e.toString()); }
}