detachedmagnifyingglass.java

《SWING HACKS》源码 作者: Joshua Marinacci,Chris Adamson 著 徐晔 译 出版: 2007年2月

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import javax.swing.*;

public class DetachedMagnifyingGlass extends JComponent 
    implements MouseMotionListener {

    double zoom;
    JComponent comp;
    Point point;
    Dimension mySize;
    Robot robot;

    public DetachedMagnifyingGlass (JComponent comp,
                                    Dimension size,
                                    double zoom) {
        this.comp = comp;
        // flag to say don't draw until we get a MouseMotionEvent
        point = new Point (-1, -1); 
        comp.addMouseMotionListener(this);
        this.mySize = size;
        this.zoom = zoom;
        // if we can't get a robot, then we just never
        // paint anything
        try {
            robot = new Robot();
        } catch (AWTException awte) {
            System.err.println ("Can't get a Robot");
            awte.printStackTrace();
        } 
    }


    public void paint (Graphics g) {
        if ((robot == null) || (point.x == -1))
        { 
            g.setColor (Color.blue);
            g.fillRect (0, 0, mySize.width, mySize.height);
            return;
        }
        Rectangle grabRect = computeGrabRect();
        BufferedImage grabImg = robot.createScreenCapture (grabRect);
        Image scaleImg = 
            grabImg.getScaledInstance (mySize.width, mySize.height, Image.SCALE_FAST);
        g.drawImage (scaleImg, 0, 0, null);
    }

    private Rectangle computeGrabRect() {
        // width, height are size of this comp / zoom
        int grabWidth = (int) ((double) mySize.width / zoom);
        int grabHeight = (int) ((double) mySize.height / zoom);
        // upper left corner is current point
        return new Rectangle (point.x, point.y, grabWidth, grabHeight);
    }


    public Dimension getPreferredSize() { return mySize; }
    public Dimension getMinimumSize() { return mySize; }
    public Dimension getMaximumSize() { return mySize; }

    // MouseMotionListener implementations
    public void mouseMoved (MouseEvent e) {
        Point offsetPoint = comp.getLocationOnScreen();
        e.translatePoint (offsetPoint.x, offsetPoint.y);
        point = e.getPoint();
        repaint();
    }
    public void mouseDragged (MouseEvent e) {
        mouseMoved (e);
    }

}