Thread: AffineTransform not working right

AffineTransform not working right. iam not sure what i am missing.

so iam trying to flip the image.

i first set up paint method so i can print my image

public void paint(Graphics g)
{
Graphics2D g2d = (Graphics2D) g;

than i set up AffineTransform

AffineTransform tx = new AffineTransform();

than i scale it neg,pos. so it will flip image.

tx.scale(-1, 1);

than i set transform

g2d.setTransform(tx);

lastly i am print the image.

g2d.drawImage(player_image, x, y, x+width, y+height, 
	50*(int)frame, 147, 50*(int)frame+50, 189 ,Sprite_Sheet.m1);
}

it should be flip but its not. any idea what i missed?

Usually when you try to flip an image like this using a scale transform, you will have to translate it as well. Think of a single image being flipped horizontally. When this happens, the flip occurs about the y axis, and so the image which used to go from 0 to the image's width now goes from 0 to the negative of the image's width. To correct for this, you would need to translate the image over. For example, my slightly larger than an sscce code:

import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
 
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.Timer;
 
public class FlipViaTransform {
   private static final String SPRITE_SHEET_SPEC = "http://www.funorb.com/img/images/game/"
         + "central/dev_diary/sprite_sheet_full.gif";
   private static final int TIMER_DELAY = 200;
   private static final int SPRITE_ROWS = 8; // an 8 x 8 sprite sheet
 
   public static void main(String[] args) {
      try {
         URL spriteSheetUrl = new URL(SPRITE_SHEET_SPEC);
         BufferedImage spriteSheet = ImageIO.read(spriteSheetUrl);
         final ImageIcon[] iconsA = new ImageIcon[64];
         final ImageIcon[] iconsB = new ImageIcon[64];
         double wD = (double) spriteSheet.getWidth() / SPRITE_ROWS;
         double hD = (double) spriteSheet.getHeight() / SPRITE_ROWS;
         int w = (int) wD;
         int h = (int) hD;
         AffineTransform at = AffineTransform.getScaleInstance(-1, 1);
         at.translate(-wD, 0);              // *********** the key is here!!! ***********
         for (int i = 0; i < SPRITE_ROWS; i++) {
            for (int j = 0; j < SPRITE_ROWS; j++) {
               int x = (int) (i * wD);
               int y = (int) (j * hD);
               BufferedImage imgA = spriteSheet.getSubimage(x, y, w, h);
               BufferedImage imgB = new BufferedImage(imgA.getWidth(),
                     imgA.getHeight(), BufferedImage.TYPE_INT_ARGB);
               Graphics2D g2 = imgB.createGraphics();
               g2.setTransform(at);
               g2.drawImage(imgA, 0, 0, null);
               g2.dispose();
 
               iconsA[j * SPRITE_ROWS + i] = new ImageIcon(imgA);
               iconsB[j * SPRITE_ROWS + i] = new ImageIcon(imgB);
            }
         }
 
         final JLabel labelA = new JLabel("Image");
         final JLabel labelB = new JLabel("Mirror Image");
 
         labelA.setVerticalTextPosition(JLabel.BOTTOM);
         labelB.setVerticalTextPosition(JLabel.BOTTOM);
         labelA.setHorizontalTextPosition(JLabel.CENTER);
         labelB.setHorizontalTextPosition(JLabel.CENTER);
         labelA.setIcon(iconsA[0]);
         labelB.setIcon(iconsB[0]);
         final JPanel panel = new JPanel(new GridLayout(1, 0));
         panel.add(labelA);
         panel.add(labelB);
         Timer spriteTimer = new Timer(TIMER_DELAY, new ActionListener() {
            int spriteIndex = 0;
 
            @Override
            public void actionPerformed(ActionEvent arg0) {
               labelA.setIcon(iconsA[spriteIndex]);
               labelB.setIcon(iconsB[spriteIndex]);
               spriteIndex++;
               spriteIndex %= iconsA.length;
            }
         });
         spriteTimer.start();
         JOptionPane.showMessageDialog(null, panel, "AffineTransform Example", JOptionPane.PLAIN_MESSAGE);
         spriteTimer.stop();
      } catch (MalformedURLException e) {
         e.printStackTrace();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

The key bit of code is the second line below:

         AffineTransform at = AffineTransform.getScaleInstance(-1, 1);
         at.translate(-wD, 0);              // *********** the key is here!!! ***********