AffineTransform - please help me out

[Sunit Naik]

Hello Ranchers,

I am using AffineTransform class to rotate an image. I need to get hold of the image coordinates at each instant, so that I can determine when the image is hitting another object. Is there any way I can get - say something like the rectangular coordinates i.e. the 4 coordinates of the image ?

I am using g2d.drawImage(image, X, Y, this) to draw the image, but X,Y are always pointing to the top left coordinate of the image.

Please help me out
Thanks

[Campbell Ritchie]

Difficult. I would suggest you don't rotate the Graphics2D object, but take a clone of it, and rotate that.
That way you will have an un-rotated object to draw your next shape.
You can certainly get the size of an Image in terms of a rectangle, and work out its bounds.

Try

Using the matrix given in the Graphics2D method to work out the 4 corners of the new image area

Work out a Rectangle (or Rectangle2D) of the same size and rotation

Try their intersects method with all the other shapes around.

There is bound to be a better way of doing it, which I don't know.

Anybody else got a better idea??

CR

[Craig Wood]

There are many ways to approach this. You can construct transforms to both locate the
rotated image and to create a transformedShape for hit–testing.
Here's an illustration of the concept. Use/move the mouse to hit–test the rotated image.
If testing for collisions with other shapes you could use something like this

Shape target = rotate.createTransformedShape(rect);
for(each possible shape to collide with)
    if(target.intersects(nextShape))
        // haveCollision

in the mouseDragged method or in (a method called from) your animation event code.

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import javax.swing.*;
import javax.swing.event.*;
 
public class RotatedHits extends JPanel implements ChangeListener {
    BufferedImage image;
    Rectangle rect;
    AffineTransform rotate = new AffineTransform();
    boolean selected = false;
 
    public RotatedHits() {
        makeImage();
        // Use this to locate the image and to transform for hit testing.
        // Change rect.x and rect.y to translate image.
        rect = new Rectangle(100, 100, image.getWidth(), image.getHeight());
        addMouseMotionListener(mml);
    }
 
    public void stateChanged(ChangeEvent e) {
        JSlider slider = (JSlider)e.getSource();
        int value = slider.getValue();
        double theta = Math.toRadians(value);
        rotate.setToRotation(theta, rect.getCenterX(), rect.getCenterY());
        repaint();
    }
 
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
                            RenderingHints.VALUE_INTERPOLATION_BICUBIC);
        AffineTransform composite =
            AffineTransform.getTranslateInstance(rect.x, rect.y);
        composite.preConcatenate(rotate);
        g2.drawRenderedImage(image, composite);
        if(selected)
            g2.setPaint(Color.red);
        g2.draw(rotate.createTransformedShape(rect));
    }
 
    private MouseMotionListener mml = new MouseMotionAdapter() {
        public void mouseMoved(MouseEvent e) {
            Point p = e.getPoint();
            boolean hovering = false;
            if(rotate.createTransformedShape(rect).contains(p)) {
                hovering = true;
                if(!selected) {
                    selected = true;
                    repaint();
                }
            }
            if(!hovering && selected) {
                selected = false;
                repaint();
            }
        }
    };
 
    private void makeImage() {
        int w = 165, h = 90;
        int type = BufferedImage.TYPE_INT_RGB;
        image = new BufferedImage(w, h, type);
        Graphics2D g2 = image.createGraphics();
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g2.setBackground(new Color(220,240,220));
        g2.clearRect(0,0,w,h);
        g2.setPaint(Color.blue);
        g2.draw(new CubicCurve2D.Double(w/4,   h*15/16, w*4/3, h/64,
                                        w/16,  h/64, w*3/4, h*2/3));
        g2.dispose();
    }
 
    private JSlider getControl() {
        JSlider slider = new JSlider(-180, 180, 0);
        slider.addChangeListener(this);
        return slider;
    }
 
    public static void main(String[] args) {
        RotatedHits test = new RotatedHits();
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(test);
        f.getContentPane().add(test.getControl(), "Last");
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }
}

[Sunit Naik]

rotate.createTransformedShape(rect) did the trick for me, I was looking for something exactly like this

Thanks a lot . . both Campbell Ritchie and Craig Wood

Javaranch rocks !