SWT中创建一个可以可拖曳的图片且实现滚动条跟随

/*******************************************************************************
* Copyright (c) 2000, 2004 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
*     IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.swt.snippets;

/*
* Composite example snippet: scroll a child control automatically
*
* For a list of all SWT example snippets see
* http://www.eclipse.org/swt/snippets/
*/
import org.eclipse.swt.*;
import org.eclipse.swt.events.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.*;

public class Snippet9 {

public static void main (String [] args) {
Display display = new Display ();
final Shell shell = new Shell (display, SWT.SHELL_TRIM | SWT.H_SCROLL | SWT.V_SCROLL);
final Composite composite = new Composite (shell, SWT.BORDER);
composite.setEnabled (false);
composite.setLayout (new FillLayout ());
composite.setSize (700, 600);
final Color red = display.getSystemColor (SWT.COLOR_RED);
composite.addPaintListener (new PaintListener() {
public void paintControl (PaintEvent e) {
e.gc.setBackground (red);
e.gc.fillOval (5, 5, 690, 590);
}
});
final ScrollBar hBar = shell.getHorizontalBar ();
hBar.addListener (SWT.Selection, new Listener () {
public void handleEvent (Event e) {
Point location = composite.getLocation ();
location.x = -hBar.getSelection ();
composite.setLocation (location);
}
});
final ScrollBar vBar = shell.getVerticalBar ();
vBar.addListener (SWT.Selection, new Listener () {
public void handleEvent (Event e) {
Point location = composite.getLocation ();
location.y = -vBar.getSelection ();
composite.setLocation (location);
}
});
shell.addListener (SWT.Resize,  new Listener () {
public void handleEvent (Event e) {
Point size = composite.getSize ();
Rectangle rect = shell.getClientArea ();
hBar.setMaximum (size.x);
vBar.setMaximum (size.y);
hBar.setThumb (Math.min (size.x, rect.width));
vBar.setThumb (Math.min (size.y, rect.height));
int hPage = size.x - rect.width;
int vPage = size.y - rect.height;
int hSelection = hBar.getSelection ();
int vSelection = vBar.getSelection ();
Point location = composite.getLocation ();
if (hSelection >= hPage) {
if (hPage <= 0) hSelection = 0;
location.x = -hSelection;
}
if (vSelection >= vPage) {
if (vPage <= 0) vSelection = 0;
location.y = -vSelection;
}
composite.setLocation (location);
}
});
final Point [] offset = new Point [1];
Listener listener = new Listener () {
public void handleEvent (Event event) {
switch (event.type) {
case SWT.MouseDown:
Rectangle rect = composite.getBounds ();
if (rect.contains (event.x, event.y)) {
Point pt1 = composite.toDisplay (0, 0);
Point pt2 = shell.toDisplay (event.x, event.y);
offset [0] = new Point (pt2.x - pt1.x, pt2.y - pt1.y);
}
break;
case SWT.MouseMove:
if (offset [0] != null) {
Point pt = offset [0];
composite.setLocation (event.x - pt.x, event.y - pt.y);
System.out.println("x : " + event.x + " y : " + event.y);
hBar.setSelection(pt.x - event.x);
vBar.setSelection(pt.y - event.y);
}
break;
case SWT.MouseUp:
offset [0] = null;
break;
}
}
};
shell.addListener (SWT.MouseDown, listener);
shell.addListener (SWT.MouseUp, listener);
shell.addListener (SWT.MouseMove, listener);
shell.setSize(600, 500);
shell.open ();
while (!shell.isDisposed()) {
if (!display.readAndDispatch ()) display.sleep ();
}
display.dispose ();
}

}