Screen Capture Recursion

**Bestsanchez** · 03-18-2012, 02:30 AM

Hey guys I saw this image today and randomly decided I wanted to try it in java. It's a little rough, but I ran it anyways and the image won't even show up, so I put the draw call in the constructor but it still won't draw, rookie mistake? And are there any other obvious mistakes?

Main class:

Java Code:

import java.awt.*;
import java.awt.image.BufferedImage;
import javax.swing.*;
 
public class RecurseScreen{
	private JFrame frame;
	private RecursePanel panel;
	private Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
	private BufferedImage image;
	
	public static void main(String[] args){
		try{
			new RecurseScreen();
		} catch(Exception e){
			e.printStackTrace();
		}
	}
	
	public RecurseScreen() throws Exception{
		frame = new JFrame();
		panel = new RecursePanel();

		
		Rectangle screenRectangle = new Rectangle(screenSize);
		Robot robot = new Robot();
		image = robot.createScreenCapture(screenRectangle);
		
		frame.setSize(screenSize.width - 100, screenSize.height -100);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setResizable(false);
		frame.setTitle("Yo dawg");
		frame.setVisible(true);
		frame.setLocationRelativeTo(null);
		frame.add(panel);
		
		panel.paintComponent(image, 0, 0, image.getWidth(), image.getHeight()); //test draw
		
		//captureScreen(0, 0);
	}
 
	public void captureScreen(int x, int y) throws Exception{

		if(x > frame.getWidth()/2){
		}else{
			panel.paintComponent(image, x, y, image.getWidth(), image.getHeight());
		
			BufferedImage img = new BufferedImage(image.getWidth() - 2*x, image.getHeight() - 2*y, image.getType()); 
			image = img;
			captureScreen(x/2 + 15, y/2 + 15);
		}
	}
}

Custom JPanel:

Java Code:

import java.awt.Graphics;
import java.awt.image.BufferedImage;

import javax.swing.*;

public class RecursePanel extends JPanel{
	private Graphics g;
	
	public void paintComponent(BufferedImage img, int x, int y, int width, int height){
		super.paintComponent(g);
		
		g.drawImage(img, x, y, width, height, null);
		repaint();
	}
}

**Fubarable** · 03-18-2012, 02:50 AM

I'm greatly surprised you're not getting a NullPointerException with that code.

**Bestsanchez** · 03-18-2012, 03:04 AM

Haha why?

**Fubarable** · 03-18-2012, 03:11 AM

Where do you initialize your Graphics object?

But regardless, if this were my program, I'd put all my energy into creating a BufferedImage, and when done, display or store the BufferedImage.

**Bestsanchez** · 03-18-2012, 03:23 AM

Oh I wasn't even looking in that class, good point, but I can't instantiate Graphics? And as for the BufferedImage, I thought that's what I was doing? Taking a screenshot and drawing it on the panel right?

**Fubarable** · 03-18-2012, 03:28 AM

Originally Posted by Bestsanchez

Oh I wasn't even looking in that class, good point, but I can't instantiate Graphics? And as for the BufferedImage, I thought that's what I was doing? Taking a screenshot and drawing it on the panel right?

Well, is your code as written working? If not, then no you're not doing this.

Again, I'd work with just the BufferedImage, including extracting its Graphics object and drawing with that.

**Bestsanchez** · 03-18-2012, 03:37 AM

In the constructor:

Java Code:

		ImageIO.write(image, "png", new File("img"));
		
		panel.paintComponent(image.getGraphics(), image, 0, 0, image.getWidth(), image.getHeight()); //test draw

It's writing just fine but still not displaying, even now that i'm extracting the graphics from the image and using that.

**Fubarable** · 03-18-2012, 03:59 AM

Again, I would separate out your Swing code from your recursive image creation code. In fact consider creating a static method that creates and returns the BufferedImage and that has no Swing code in it. Then have your GUI call the method when it wishes, and take the image and either write it to disk or display it in a JLabel's ImageIcon. Your current code can't display anything since your JPanel doesn't have a valid paintComponent override method.

**Fubarable** · 03-18-2012, 04:26 AM

A pseudo-code solution that just now worked for me is to create a recursiveDraw method with this signature:

Java Code:

private static void recursiveDraw(BufferedImage img, Graphics imgG, double scale) {

and with the following logic

Java Code:

start recursiveDraw method
  // most important: all recursions must have a good ending condition:
  get img height and width. If either <= a min, return 

  create a BufferedImage, smlImg, for the smaller image using the height, width and scale factor
  Get the Graphics object, smlG, from the small image
  Use smlG.drawImage(...) overload to draw the big image in shrunken form onto the little image
  recursively call recursiveDraw passing in smlImg, smlG, and scale.
  dispose of smlG
  draw smlImg (the small image) onto the bigger one using the bigger's Graphics object (passed
     into this method) and a different overload of the drawImage method.
end recursiveDraw method