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Thread: AffineTransform not working right

  1. #1
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    Default 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?


  2. #2
    Super Moderator curmudgeon's Avatar
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    Default Re: AffineTransform not working right

    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!!! ***********

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