Java 1.2 How-To/JavaHowTo.iso/javafile/ch07/LayerApp.java

Java Source | 1998-12-14 | 5.7 KB | 282 lines

import java.awt.*;
import java.awt.event.*;
import java.applet.Applet;
import java.awt.image.*;

/*
 * class for handling one image
 */
class Picture {

/*
 * position of the image
 */
int xpos, ypos;

/*
 * width and height of the image
 */
int width, height;

/*
 * the image itself
 */
Image image;
ImageObserver obs;

/**
 * constructor saves arguments
 * @param img - the image
 * @param x, y - initial position
 * @param o - imageObserver of parent
 */
public Picture (Image img, int x, int y, ImageObserver o) {

    image = img;
    xpos = x;
    ypos = y;
    obs = o;
    width = image.getWidth (obs);
    height = image.getHeight (obs);
}

/**
 * determine whether the point is inside this image
 * @param x, y - coordinate of point
 */
boolean inside (int x, int y) {

    if (x < xpos || x > (xpos+width)) return false;
    if (y < ypos || y > (ypos+height)) return false;
    return true;
}

/**
 * set the current position of the image
 * @param x, y - position to set
 */
void setPosition (int x, int y) {

    xpos = x;
    ypos = y;
}

/**
 * draw the image
 * draw a green border around the image if
 * highlight is true
 * @param g - destination graphics object
 * @param highlight - draw border
 */
void paint (Graphics g, boolean highlight) {

    if (highlight) {
        g.setColor (Color.green);
        g.fillRect (xpos-5, ypos-5, width+10, height+10);
    }
    g.drawImage (image, xpos, ypos, obs);
}
}

/*
 * the applet
 */
public class LayerApp extends Applet implements MouseListener,
        MouseMotionListener, ActionListener
{

/*
 * the number of picture objects
 */
final int NPictures = 4;

/*
 * an array containing the picture objects
 */
Picture pictures[] = new Picture[NPictures];

/*
 * the user-selected picture
 */
int selectedPic = -1;

/*
 * offsets from mouse to image origin
 */
int dx, dy;

/*
 * offscreen image for double-buffering
 */
Image offimg;
Button btnBring;
Button btnSend;

/*
 * offscreen graphics context associated with
 * offscreen image
 */
Graphics offg;

/*
 * dimension of offscreen image
 */
Dimension offsize;

/*
 * called when the applet is loaded
 */
public void init() {

    setLayout(new BorderLayout());

    Panel p = new Panel ();
    add ("South", p);
    btnBring = new Button("Bring to front");
    btnSend = new Button("Send to back");
    p.add(btnBring);
    p.add(btnSend);
    addMouseListener(this);
    addMouseMotionListener(this);
    btnBring.addActionListener(this);
    btnSend.addActionListener(this);

    int i;
    Image img;
    String name;
    MediaTracker tracker = new MediaTracker (this);

    offsize = getSize();
    offimg = createImage (offsize.width, offsize.height);
    offg = offimg.getGraphics();

    for (i=0; i<NPictures; i+=1) {
                if (i < 2) name = "T"+(i+1)+".jpg";
                else name = "T"+(i+1)+".gif";
        img = getImage (getDocumentBase(), name);
        tracker.addImage (img, i);
        showStatus ("Getting image: "+name);
        try {
            tracker.waitForID (i);
        } catch (InterruptedException e) { }
        pictures[i] = new Picture (img, i*10, i*20, this);
    }
}

/**
 * reverse the order of update for efficiency
 * @param g - destination graphics object
 */
public void paint (Graphics g) {

    update (g);
}

/**
 * override update to avoid erase flicker
 * @param g - destination graphics object
 */
public void update (Graphics g) {

    int i;

    offg.setColor (Color.black);
    offg.fillRect (0, 0, offsize.width, offsize.height);
    for (i=0; i<NPictures; i+=1) {
        if (i == selectedPic) pictures[i].paint (offg, true);
        else pictures[i].paint (offg, false);
    }
    g.drawImage(offimg, 0, 0, this);
}

/**
 * determine which image the user clicked
 * @param evt - event object
 * @param x, y - mouse position
 */
public void mouseClicked(MouseEvent e){}
public void mouseEntered(MouseEvent e){}
public void mouseExited(MouseEvent e){}

public void mouseReleased(MouseEvent e)
{
    repaint ();
}

public void mouseMoved(MouseEvent e){}

public void mousePressed(MouseEvent e)
{
    int x =e.getX();
    int y =e.getY();

    int i;

    selectedPic = -1;
    for (i=NPictures-1; i>=0; i-=1)
    {
        if (pictures[i].inside (x, y))
        {
            selectedPic = i;
            dx = x - pictures[i].xpos;
            dy = y - pictures[i].ypos;
            break;
        }
    }
}

public void mouseDragged(MouseEvent e)
{
    int x =e.getX();
    int y =e.getY();
    int i;

    if (selectedPic < 0) return;
    /* for (i=NPictures-1; i>=0; i-=1)
    {

        pictures[selectedPic].setPosition (x - dx, y - dy);
        repaint ();
    } */

}
/**
 * reorder the images depending on which button is pressed
 * @param evt - event object
 * @param arg - target object
 */
public void actionPerformed(ActionEvent evt)
{
    Object object1 = evt.getSource();
    int i;
    Picture temp;


    if (object1 == btnBring) {
        if (selectedPic < 0) return;
        temp = pictures[selectedPic];
        for (i=selectedPic; i<NPictures-1; i+=1)
        {
            pictures[i] = pictures[i+1];
        }
        pictures[NPictures-1] = temp;
        selectedPic = NPictures - 1;
        repaint ();
        return;
    }
    if (object1 == btnSend)
    {
        if (selectedPic < 0) return;
        temp = pictures[selectedPic];
        for (i=selectedPic; i>0; i-=1)
        {
            pictures[i] = pictures[i-1];
        }
        pictures[0] = temp;
        selectedPic = 0;
        repaint ();
        return;
    }
}
}