Trying to paint image to JFrame with Java BufferedImage, Graphics

Question

I'm trying to capture the screen and then paint the image to a JFrame recursively while scaling the image (to create that effect you get when you look at a mirror in a mirror).

I'm having trouble with my code - it doesn't paint any graphics. What am I doing wrong?

import java.awt.AWTException;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.HeadlessException;
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.image.BufferedImage;

import javax.swing.JFrame;


public class ScreenCapture extends JFrame {

    BufferedImage screenCapture;
    Graphics screenCaptureGraphics;
    private static int recurseCount = 0;
    private static float $scale = 0.9f;
    private static float scale = 1.0f;
    private static int height;
    private static int width;

    ScreenCapture() {
        try {
            screenCapture = new Robot().createScreenCapture(
                       new Rectangle(Toolkit.getDefaultToolkit().getScreenSize()) );
            height = screenCapture.getHeight();
            width = screenCapture.getWidth();
            setSize(new Dimension(width, height));
            addWindowListener(new LocalWindowListener());
            Graphics g = recursiveDraw(screenCapture, getGraphics());
            paint(g);
        } catch (HeadlessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (AWTException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    private Graphics recursiveDraw(BufferedImage img, Graphics imgG) {
        updateScale(++recurseCount);
        float newWidth = scale*width;
        float newHeight = scale*height;
        int w = (int) newWidth;
        int h = (int) newHeight;
        System.out.println("W: " + w + "; H: " + h);
        if (w >= 10 && h >= 10) {
            //scale image
            System.out.print("Creating scaled Image...");
            Image scaled = img.getScaledInstance(w, h, Image.SCALE_SMOOTH);
            BufferedImage resized = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
            imgG = resized.createGraphics();
            imgG.drawImage(scaled, 0, 0, null);
            System.out.println("...Image drawn to graphics");
            //return new graphics
            return recursiveDraw(resized, imgG);
        } else {
            //otherwise return old graphics
            System.out.println("Completed.");
            return imgG;
        }
    }


    private void updateScale(int count) {
        for (int i=0; i<count; i++) {
            scale *= $scale;
        }
        System.out.println("Updated scale: " + scale + "; Recurse count: " + recurseCount);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new ScreenCapture().setVisible(true);
            }
        });
    }

    private class LocalWindowListener extends WindowAdapter {
        @Override
        public void windowClosing(WindowEvent e) {
            System.exit(0); return;
        }
    }

}

EDIT: This is what I tried after @andrew-thompson 's answer:

ScreenCapture() {
    try {
        screenCapture = new Robot().createScreenCapture(
                   new Rectangle(Toolkit.getDefaultToolkit().getScreenSize()) );
        height = screenCapture.getHeight();
        width = screenCapture.getWidth();
        setSize(new Dimension(width, height));
        addWindowListener(new LocalWindowListener());
        setLayout(new GridLayout());
        add(new PaintPanel());
    } catch (HeadlessException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (AWTException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

private class PaintPanel extends JPanel {
    @Override
    public void paintComponent(Graphics g) {
        g=recursiveDraw(screenCapture, g);
        //what to do with g?
    }
}

I still have the same problem where I don't know how to make the BufferedImage paint to the graphics.

Answer 1

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.

When I did this (today in fact), I created a recursive method with this signature

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

and with this method body (in pseudo-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

This algorithm resulted in images like:

For example:

import java.awt.*;
import java.awt.Dialog.ModalityType;
import java.awt.event.ActionEvent;
import java.awt.image.BufferedImage;
import javax.swing.*;

public class RecursiveDrawTest {
   private static final Color BACKGRND_1 = Color.green;
   private static final Color BACKGRND_2 = Color.MAGENTA;
   private static final Color FOREGRND_1 = Color.blue;
   private static final Color FOREGRND_2 = Color.RED;

   private static void createAndShowGui() {
      final JPanel mainPanel = new JPanel(new BorderLayout());
      final JSlider slider = new JSlider(50, 90, 65);
      slider.setMajorTickSpacing(10);
      slider.setMinorTickSpacing(5);
      slider.setPaintLabels(true);
      slider.setPaintTicks(true);

      JPanel southPanel = new JPanel();
      southPanel.add(new JLabel("Percent Size Reduction:"));
      southPanel.add(slider);
      southPanel.add(new JButton(new AbstractAction("Create Recursive Image") {

         @Override
         public void actionPerformed(ActionEvent arg0) {
            try {
               double scale = slider.getValue() / 100.0;
               BufferedImage img = createRecursiveImg(scale);
               ImageIcon icon = new ImageIcon(img);
               JLabel label = new JLabel(icon);

               Window win = SwingUtilities.getWindowAncestor(mainPanel);
               JDialog dialog = new JDialog(win, "Image", ModalityType.MODELESS);
               dialog.getContentPane().add(label);
               dialog.pack();
               dialog.setLocationRelativeTo(null);
               dialog.setVisible(true);
            } catch (AWTException e) {
               e.printStackTrace();
            }
         }
      }));

      mainPanel.add(new JScrollPane(new JLabel(new ImageIcon(createLabelImg()))), 
            BorderLayout.CENTER);
      mainPanel.add(southPanel, BorderLayout.PAGE_END);

      JFrame frame = new JFrame("RecursiveDrawTest");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   // create a background image to display in a JLabel so that the GUI
   // won't be boring.
   private static BufferedImage createLabelImg() {
      Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
      int width = (5 * d.width) / 6;
      int height = (5 * d.height) / 6;
      BufferedImage img = new BufferedImage(width, height, 
            BufferedImage.TYPE_INT_ARGB);
      Graphics2D g2 = img.createGraphics();
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
      g2.setPaint(new GradientPaint(0, 0, BACKGRND_1, 40, 40, BACKGRND_2, true));
      g2.fillRect(0, 0, width, height);
      g2.setPaint(new GradientPaint(0, height, FOREGRND_1, 40, height - 40, FOREGRND_2, true));
      g2.fillOval(0, 0, 2 * width, 2 * height);
      g2.dispose();
      return img;
   }

   // non-recursive image to get the initial image that will be drawn recursively
   public static BufferedImage createRecursiveImg(double scale) throws AWTException {
      Robot robot = new Robot();
      Dimension screenSz = Toolkit.getDefaultToolkit().getScreenSize();
      Rectangle screenRect = new Rectangle(screenSz);
      BufferedImage img = robot.createScreenCapture(screenRect);
      Graphics g = img.getGraphics();
      recursiveDraw(img, g, scale); // call recursive method
      g.dispose();
      return img;
   }

   // recursive method to draw image inside of image
   private static void recursiveDraw(BufferedImage img, Graphics g, double scale) {
      int w = img.getWidth();
      int h = img.getHeight();

      int smlW = (int)(w * scale);
      int smlH = (int)(h * scale);
      // criteria to end recursion
      if (smlW <= 1 || smlH <= 1) {
         return; 
      }

      BufferedImage smlImg = new BufferedImage(smlW, smlH, BufferedImage.TYPE_INT_ARGB);
      Graphics smlG = smlImg.getGraphics();
      // draw big image in little image, scaled to little image
      smlG.drawImage(img, 0, 0, smlW, smlH, null);

      // recursive call
      recursiveDraw(smlImg, smlG, scale);
      smlG.dispose(); // clear resources when done with them

      // these guys center the smaller img on the bigger
      int smlX = (w - smlW) / 2;
      int smlY = (h - smlH) / 2;
      // draw small img on big img
      g.drawImage(smlImg, smlX, smlY, smlW, smlH, null);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

Answer 2

 Graphics g = recursiveDraw(screenCapture, getGraphics());

Don't call getGraphics(). Override paint(Graphics)¹ & use the supplied Graphics instance.

1. When using Swing, it is actually best to override the paintComponent(Graphics) method of a JComponent or JPanel. Then add that to the top-level container.