我已经阅读了很多关于绘制图像的文章，但是当我需要保留背景时，我无法让它们工作。我点击JButton后试图旋转另一张图像上的图像。背景图像在JPanel上生成：
public void paintComponent(Graphics g){
int index = 0;
Graphics2D g2 = (Graphics2D) g;
super.paintComponent(g);
try {
image = ImageIO.read(url1);
image2 = ImageIO.read(url2);
image3 = ImageIO.read(url3);
} catch (IOException e) {
}
g.drawImage(image, 0, 0, null);
g.drawImage(image3, 0, 0, null);
if(scaleDrawnFlag == 0){
for(index = 0; index < 60; index ++){
tx = AffineTransform.getRotateInstance(Math.toRadians(6*index), this.getHeight()/2, this.getWidth()/2);
op = new AffineTransformOp(tx, AffineTransformOp.TYPE_BILINEAR);
g.drawImage(op.filter(image3, null), 0, 0, null);
}
scaleDrawnFlag = 1;
}
g.drawImage(image2, 0, 0, null);
}
这是一个JPanel命名面板，只绘制一次图像以保持刷新性能，仅适用于动画图像。这为转速表绘制了一个刻度，总共60行，其中每一行都是image3的副本
动画图像是通过按下JButton生成的，由以下内容生成：
public void paintComponent(Graphics g){
super.paintComponent(g);
BufferedImage img = new BufferedImage(370, 370, BufferedImage.TRANSLUCENT);
Graphics2D g2d = img.createGraphics();
g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.CLEAR, 0.0f));
g2d.fillRect(0, 0, img.getWidth(), img.getHeight());
g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.0f));
Graphics2D temp = (Graphics2D) g;
tx = AffineTransform.getRotateInstance(Math.toRadians(degrees), this.getHeight()/2, this.getWidth()/2);
op = new AffineTransformOp(tx, AffineTransformOp.TYPE_BILINEAR);
temp.drawImage(op.filter(image2, null), 0, 0, null);
temp.dispose();
}
这是另一个名为overPanel的JPanel，它位于最初的JPanel之上。
但是，当我打电话给方法时：
public void up(){
degrees ++;
if(degrees == 360) degrees = 0;
repaint();
}
public void down(){
degrees --;
if(degrees == -360) degrees = 0;
repaint();
}
在overPanel类中，JPanel完全被清除。动画效果很好，但背景消失了。
我该怎样做才能保留背景？
我还尝试了另一种解决方案，在每次up（）和down（）调用时再次绘制60行。背景重新绘制，但需要花费太多时间才能完成，因此，旋转转速计指示器的动画会滞后。
答案 0 :(得分：3)
永远不要丢弃JVM提供给您的Graphics对象。你这样做了：
// temp **is** the same object as g and is the Graphics object given by the JVM
Graphics2D temp = (Graphics2D) g;
//....
temp.dispose();
并且不应该这样做，因为它完全打破了绘画链。你应该处理你创建的g2d对象。
此外，这也没关系
Graphics2D temp = (Graphics2D) g.create(); // temp **is** a new object
//....
temp.dispose(); // this is OK
其他问题：
paintComponent方法为protected，而非public。避免不必要地增加其可见性。在您的最小示例程序中，您的scaleDrawnFlag变量及其关联的if-block似乎搞砸了您。该变量和if块的目的是什么？如果你摆脱变量和if块，你的背景将会持续存在。我自己，我会通过创建一个稳定的背景图像并在每次paintComponent(...)方法中绘制它来做不同的事情。我不会覆盖update(...)，因为它是AWT kludge而不是Swing图形。我也试图避免null布局和setBounds(...)像瘟疫一样，因为这导致了非常灵活，严格的GUI，很难调试，维护和增强。例如：
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.geom.AffineTransform;
import java.awt.image.AffineTransformOp;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.*;
@SuppressWarnings("serial")
public class MyMainPanel extends JPanel {
private MyDrawingPanel myDrawingPanel;
public MyMainPanel() {
try {
myDrawingPanel = new MyDrawingPanel();
} catch (IOException e) {
e.printStackTrace();
System.exit(-1);
}
JPanel rightPanel = new JPanel();
rightPanel.setLayout(new GridLayout(0, 1, 5, 5));
rightPanel.add(new JButton(new MyUpAction("Up", KeyEvent.VK_U)));
rightPanel.add(new JButton(new MyDownAction("Down", KeyEvent.VK_D)));
JPanel rightWrapPanel = new JPanel(new BorderLayout());
rightWrapPanel.add(rightPanel, BorderLayout.PAGE_START);
setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
setLayout(new BorderLayout());
add(myDrawingPanel, BorderLayout.CENTER);
add(rightWrapPanel, BorderLayout.LINE_END);
}
private class MyUpAction extends AbstractAction {
public MyUpAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
}
@Override
public void actionPerformed(ActionEvent e) {
myDrawingPanel.up();
}
}
private class MyDownAction extends AbstractAction {
public MyDownAction(String name, int mnemonic) {
super(name);
putValue(MNEMONIC_KEY, mnemonic);
}
@Override
public void actionPerformed(ActionEvent e) {
myDrawingPanel.down();
}
}
private static void createAndShowGui() {
JFrame frame = new JFrame("MyMainPanel");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new MyMainPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
@SuppressWarnings("serial")
class MyDrawingPanel extends JPanel {
private static final String NEEDLE_IMG_PATH = "http://1.bp.blogspot.com/"
+ "-fq-oPGBSLp4/Ttoj7DoAMWI/AAAAAAAABtc/t7gKJlfRQuo/s400/secondHand.png";
private static final String ORANGE_DISK_IMG_PATH = "http://upload.wikimedia.org/wikipedia/commons/thumb/b/b6/Circle_Fulvous_Solid.svg/200px-Circle_Fulvous_Solid.svg.png";
private static final String GREEN_LINE_IMG_PATH = "http://www.xtremeskater.com/math/images/circle_radius.png";
private static final int MAX_DEGREES = 360;
private int imgWidth = 0;
private int imgHeight = 0;
private BufferedImage needleImg = null;
private BufferedImage orangeDiskImg = null;
private BufferedImage greenLineImg = null;
private BufferedImage backgroundImg = null;
private int degrees;
public MyDrawingPanel() throws IOException {
URL needleUrl = new URL(NEEDLE_IMG_PATH);
URL orangeDiskUrl = new URL(ORANGE_DISK_IMG_PATH);
URL greenLineUrl = new URL(GREEN_LINE_IMG_PATH);
needleImg = ImageIO.read(needleUrl);
orangeDiskImg = ImageIO.read(orangeDiskUrl);
greenLineImg = ImageIO.read(greenLineUrl);
imgWidth = Math.max(orangeDiskImg.getWidth(),
greenLineImg.getWidth());
imgHeight = Math.max(orangeDiskImg.getHeight(),
greenLineImg.getHeight());
backgroundImg = new BufferedImage(imgWidth, imgHeight,
BufferedImage.TYPE_INT_ARGB);
Graphics2D g2 = backgroundImg.createGraphics();
drawBackground(g2, imgWidth, imgHeight);
g2.dispose();
}
@Override
public Dimension getPreferredSize() {
if (isPreferredSizeSet()) {
return super.getPreferredSize();
}
return new Dimension(imgWidth, imgHeight);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (backgroundImg != null) {
g.drawImage(backgroundImg, 0, 0, null);
}
AffineTransform tx = AffineTransform.getRotateInstance(Math.toRadians(degrees),
this.getHeight() / 2, this.getWidth() / 2);
AffineTransformOp op = new AffineTransformOp(tx, AffineTransformOp.TYPE_BILINEAR);
g.drawImage(op.filter(needleImg, null), 0, 0, null);
}
public void up() {
degrees++;
degrees %= MAX_DEGREES;
repaint();
}
public void down() {
degrees--;
degrees += MAX_DEGREES;
degrees %= MAX_DEGREES;
repaint();
}
public int getDregrees() {
return degrees;
}
private void drawBackground(Graphics2D g2, int biWidth, int biHeight) {
int index;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2.drawImage(orangeDiskImg, 0, 0, null);
g2.drawImage(greenLineImg, 0, 0, null);
AffineTransform tx = AffineTransform.getRotateInstance(Math.toRadians(6),
biWidth / 2, biHeight / 2);
for (index = 0; index < 60; index++) {
g2.transform(tx);
g2.drawImage(greenLineImg, 0, 0, null);
}
}
}
答案 1 :(得分：0)
我找到了使背景永久化的方法，首先将其创建为Buffered图像，然后在每个动作上重新绘制该图像，而不重绘所有原始形式或图像旋转。我的意思是，首先，我创建了多次旋转基本图像的背景。这是使用缓冲图像创建的。然后，在paintComponent()方法上，我重绘了缓冲的图像：
public MyPanel(){
try {
image = ImageIO.read(url1);
image2 = ImageIO.read(url2);
image3 = ImageIO.read(url3);
} catch (IOException e) {
}
img = createImage();
}
private Image createImage(){
double index = 0;
BufferedImage bufferedImage = new BufferedImage(370,370,BufferedImage.TYPE_INT_ARGB);
Graphics g = bufferedImage.getGraphics();
for(index = 0; index <= scale; index = index + count){
tx = AffineTransform.getRotateInstance(Math.toRadians(deg2), 185, 185);
op = new AffineTransformOp(tx, AffineTransformOp.TYPE_BILINEAR);
g.drawImage(op.filter(image3, null), 0, 0, null);
deg2 = deg2 + (270.0/(scale/count));
}
return bufferedImage;
}
protected void paintComponent(Graphics g){
super.paintComponent(g);
g.drawImage(image, 0, 0, null); //Indicator drawing
g.drawImage(img, 0, 0, null); //Scale drawing
//Indicator rotation
tx = AffineTransform.getRotateInstance(Math.toRadians(degrees), this.getHeight()/2, this.getWidth()/2);
op = new AffineTransformOp(tx, AffineTransformOp.TYPE_BILINEAR);
g.drawImage(op.filter(image2, null), 0, 0, null);
}
这里是基本示例的完整代码：
package rotateOnImage;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Image;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JButton;
import javax.swing.AbstractAction;
import java.awt.event.ActionEvent;
import java.awt.geom.AffineTransform;
import java.awt.image.AffineTransformOp;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import javax.swing.Action;
public class MainFrame extends JFrame {
/**
*
*/
private static final long serialVersionUID = 1L;
private JPanel contentPane;
private MyPanel panel = new MyPanel();
private final Action upAction = new upAction();
private final Action dnAction = new dnAction();
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
MainFrame frame = new MainFrame();
frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public MainFrame() {
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 345, 227);
contentPane = new JPanel();
contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(contentPane);
contentPane.setLayout(null);
JButton btnNewButton = new JButton("UP");
btnNewButton.setAction(upAction);
btnNewButton.setBounds(212, 12, 117, 25);
contentPane.add(btnNewButton);
JButton button = new JButton("DN");
button.setAction(dnAction);
button.setBounds(212, 49, 117, 25);
contentPane.add(button);
panel.setBounds(0, 0, 200, 200);
contentPane.add(panel);
}
private class upAction extends AbstractAction {
/**
*
*/
private static final long serialVersionUID = 1L;
public upAction() {
putValue(NAME, "UP");
}
public void actionPerformed(ActionEvent e) {
panel.up();
}
}
private class dnAction extends AbstractAction {
/**
*
*/
private static final long serialVersionUID = 1L;
public dnAction() {
putValue(NAME, "DN");
}
public void actionPerformed(ActionEvent e) {
panel.down();
}
}
}
class MyPanel extends JPanel{
private static final long serialVersionUID = 1L;
/**
*
*/
private int degrees = 0;
private AffineTransform tx = null;
private AffineTransformOp op = null;
private BufferedImage image1 = null;
private BufferedImage image2 = null;
private BufferedImage image3 = null;
Image img = null;
public static final String IMAGE_PATH1 = "http://1.bp.blogspot.com/"+"-fq-oPGBSLp4/Ttoj7DoAMWI/AAAAAAAABtc/t7gKJlfRQuo/s400/secondHand.png";
public static final String IMAGE_PATH2 = "http://upload.wikimedia.org/wikipedia/commons/thumb/b/b6/Circle_Fulvous_Solid.svg/200px-Circle_Fulvous_Solid.svg.png";
public static final String IMAGE_PATH3 ="http://www.xtremeskater.com/math/images/circle_radius.png";
public MyPanel(){
try {
URL url1 = new URL(IMAGE_PATH1);
URL url2 = new URL(IMAGE_PATH2);
URL url3 = new URL(IMAGE_PATH3);
image1 = ImageIO.read(url1);
image2 = ImageIO.read(url2);
image3 = ImageIO.read(url3);
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
img = createImage();
}
public void up(){
degrees ++;
if(degrees == 360) degrees = 0;
repaint();
}
public void down(){
degrees --;
if(degrees == -360) degrees = 0;
repaint();
}
public int getDregrees(){
return degrees;
}
private Image createImage(){
double index = 0.0;
BufferedImage bufferedImage = new BufferedImage(200,200,BufferedImage.TYPE_INT_ARGB);
Graphics g = bufferedImage.getGraphics();
for(index = 0.0; index <= 36; index ++){
tx = AffineTransform.getRotateInstance(Math.toRadians(index*10), 100, 100);
op = new AffineTransformOp(tx, AffineTransformOp.TYPE_BILINEAR);
g.drawImage(op.filter(image3, null), 0, 0, null);
}
return bufferedImage;
}
public void update(Graphics g){
paint(g);
}
protected void paintComponent(Graphics g){
super.paintComponent(g);
g.drawImage(image2, 0, 0, null); //Dibujado de la manecilla
g.drawImage(img, 0, 0, null); //Dibujado de la escala
//Rotación de la manecilla
tx = AffineTransform.getRotateInstance(Math.toRadians(degrees), this.getHeight()/2, this.getWidth()/2);
op = new AffineTransformOp(tx, AffineTransformOp.TYPE_BILINEAR);
g.drawImage(op.filter(image1, null), 0, 0, null);
}
}