我正在尝试使用 Java 6/7 编写可重用的 JPanel 图像查看器。如果在调整大小期间不移动 JPanel的左上角（视口原点），我可以使用 mouseDragged 实现图像拖动，也可以调整 JPanel 的大小以裁剪或显示图像。注意我不想调整图像大小以适应面板。我希望图像在调整面板大小以裁剪它时保持固定在屏幕上。
如果我拖动框架的左边缘并因此移动视口原点，即使我在调整大小期间动态重新计算图像原点，在调整大小操作期间也会出现相当大的图像抖动。这似乎是由于在调用paintComponent() 的时间和通过调用drawImage() 实际渲染图像的时间之间的视口原点发生了变化。关于如何消除所说的抖动的任何想法？提前致谢。
下面的两个类应该演示该行为：
/***** ImageViewer.java *****/
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.image.BufferedImage;
import javax.swing.*;
import java.awt.event.*;
import java.io.*;
import javax.imageio.ImageIO;
public class ImageViewer extends JFrame
{
private ImagePanel canvas;
private BufferedImage theImage;
private JFileChooser theChooser;
public ImageViewer( BufferedImage bi )
{
canvas= new ImagePanel( );
add( canvas, BorderLayout.CENTER );
JPanel control= new JPanel();
JButton loadBtn= new JButton( "Load Image" );
control.add( loadBtn );
add( control, BorderLayout.NORTH );
loadBtn.addActionListener( new ActionListener() {
public void actionPerformed( ActionEvent e )
{ doLoad(); }
});
theChooser= new JFileChooser();
}
public void doLoad()
{
File iFile = null;
int retVal = theChooser.showOpenDialog(this);
if (retVal == JFileChooser.APPROVE_OPTION) {
iFile = theChooser.getSelectedFile();
try {
theImage = ImageIO.read(iFile);
} catch (FileNotFoundException ie) {
System.err.println("File not found");
System.exit(1);
} catch (IOException ie) {
System.err.println("IOException");
System.exit(1);
}
canvas.setImage( theImage );
repaint();
}
}
/**
* @param args
*/
public static void main(String[] args)
{
BufferedImage bImage= null;
ImageViewer theApp= new ImageViewer( bImage );
theApp.setDefaultCloseOperation(EXIT_ON_CLOSE);
theApp.pack();
theApp.setVisible( true );
}
}
/***** ImagePanel.java *****/
import java.awt.Color;
import java.awt.Component;
import java.awt.Cursor;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.JPanel;
public class ImagePanel extends JPanel
{
private BufferedImage theImage;
private Dimension preferredSize;
private double scaleF = 1.0; // image scaling factor
private Point2D.Double deltaLoc; // dx, dy in scaled units for image upper
// left corner from origin to current loc
// inside or outside viewport
private Point panelLastLoc; // last location of upper left corner of the
// viewport in screen coordinates
private int lastX;
private int lastY;
private PanelState state = PanelState.IDLE;
public enum PanelState
{
IDLE, RESIZING, PMOVING, IMOVING
};
public ImagePanel()
{
setBackground(Color.GRAY);
preferredSize = new Dimension(400, 400);
addHierarchyListener(new HierarchyListener() {
public void hierarchyChanged(HierarchyEvent he)
{
doComponentChanged(he);
}
});
addHierarchyBoundsListener(new HierarchyBoundsAdapter() {
public void ancestorMoved(HierarchyEvent he)
{
doComponentMoved();
}
public void ancestorResized(HierarchyEvent he)
{
doAncestorResizing();
}
});
addComponentListener(new ComponentAdapter() {
public void componentResized(ComponentEvent ce)
{
doComponentResized();
}
});
addMouseListener(new MouseAdapter() {
public void mousePressed(MouseEvent me)
{
setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));
state = PanelState.IMOVING;
lastX = me.getX();
lastY = me.getY();
}
public void mouseReleased(MouseEvent me)
{
setCursor(Cursor.getDefaultCursor());
state = PanelState.IDLE;
}
});
addMouseMotionListener(new MouseMotionAdapter() {
public void mouseDragged(MouseEvent me)
{
doImageMoved(me);
}
});
}
public ImagePanel(BufferedImage bi)
{
theImage = bi;
preferredSize = new Dimension(theImage.getWidth(), theImage.getHeight());
}
public Dimension getPreferredSize()
{
return preferredSize;
}
private void doComponentChanged(HierarchyEvent he)
{
if (isShowing()) {
panelLastLoc = getLocationOnScreen();
}
state = PanelState.IDLE;
}
private void doImageMoved(MouseEvent me)
{
if (!isShowing() || theImage == null)
return;
switch (state)
{
case RESIZING:
error("IMOVING->RESIZING");
break;
case PMOVING:
error("IMOVING->PMOVING");
break;
case IDLE:
error("IMOVING->IDLE");
break;
case IMOVING:
if (contains(me.getX(), me.getY())) {
int dx = me.getX() - lastX;
int dy = me.getY() - lastY;
lastX = me.getX();
lastY = me.getY();
deltaLoc.x += dx;
deltaLoc.y += dy;
repaint();
}
return;
}
}
private void doComponentMoved()
{
if (!isShowing() || theImage == null)
return;
switch (state)
{
case RESIZING:
return;
case IMOVING:
error("IMOVING->PMOVING");
break;
case PMOVING:
case IDLE:
panelLastLoc = getLocationOnScreen();
state = PanelState.PMOVING;
}
return;
}
private void doAncestorResizing()
{
if (!isShowing() || theImage == null)
return;
switch (state)
{
case IMOVING:
error("IMOVING->RESIZING");
return;
case RESIZING:
case PMOVING:
case IDLE:
Point cLoc = getLocationOnScreen();
state = PanelState.RESIZING;
if (theImage != null) {
deltaLoc.x -= cLoc.x - panelLastLoc.x;
deltaLoc.y -= cLoc.y - panelLastLoc.y;
}
panelLastLoc = cLoc;
}
}
private void doComponentResized()
{
Point cLoc = getLocationOnScreen();
switch (state)
{
case RESIZING:
state = PanelState.IDLE;
break;
case IMOVING:
error("IMOVING->RESIZED");
break;
case PMOVING:
state = PanelState.IDLE;
break;
case IDLE:
break;
}
if (theImage != null) {
deltaLoc.x -= cLoc.x - panelLastLoc.x;
deltaLoc.y -= cLoc.y - panelLastLoc.y;
}
panelLastLoc = cLoc;
}
public void setImage(BufferedImage nI)
{
theImage = nI;
scaleF = 1.0;
state = PanelState.IDLE;
deltaLoc = new Point2D.Double(Math.round((getWidth() - theImage.getWidth()) / 2.0),
Math.round((getHeight() - theImage.getHeight()) / 2.0));
panelLastLoc = getLocationOnScreen();
}
private void error(String em)
{
System.err.println(em);
System.exit(1);
}
public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
if (theImage == null)
return;
/*
* Check if the viewport has resized or moved. The check below is
* performed on every repaint.
*/
Point cLoc = getLocationOnScreen();
Dimension cDim = getSize();
if (state == PanelState.RESIZING || state == PanelState.IDLE) {
deltaLoc.x -= cLoc.x - panelLastLoc.x;
deltaLoc.y -= cLoc.y - panelLastLoc.y;
}
/*
System.err.println("image left edge= "
+ Math.round(cLoc.x + deltaLoc.x) + "; state= " + state
+ "; cDim= " + cDim + "; cLoc= " + cLoc + "; pLLoc= "
+ panelLastLoc + "; dLoc= " + deltaLoc);
*/
// In all cases update panelLastLoc
panelLastLoc = cLoc;
g2.drawImage(theImage, (int) Math.round(deltaLoc.x),
(int) Math.round(deltaLoc.y), null);
}
}