我正在尝试在我的一个程序中创建一个小绘图板。这是课程：
class DrawPad extends JComponent {
Image image;
Graphics2D graphics;
int currentX, currentY, oldX, oldY;
public DrawPad() {
setDoubleBuffered(false);
addMouseListener(new MouseAdapter() {
@Override
public void mousePressed(MouseEvent e) {
oldX = e.getX();
oldY = e.getY();
}
});
addMouseMotionListener(new MouseMotionAdapter() {
@Override
public void mouseDragged(MouseEvent e) {
currentX = e.getX();
currentY = e.getY();
if (graphics != null) {
graphics.drawLine(oldX, oldY, currentX, currentY);
}
repaint();
oldX = currentX;
oldY = currentY;
}
});
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
if (image == null) {
image = createImage(getSize().width, getSize().height);
graphics = (Graphics2D) image.getGraphics();
graphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
clear();
}
g.drawImage(image, 0, 0, null);
}
public void clear() {
graphics.setPaint(Color.white);
graphics.fillRect(0, 0, getSize().width, getSize().height);
graphics.setPaint(Color.black);
repaint();
}
public void undo() {
// restore previous graphics here
}
public void red() {
graphics.setPaint(Color.red);
repaint();
}
public void black() {
graphics.setPaint(Color.black);
repaint();
}
public void magenta() {
graphics.setPaint(Color.magenta);
repaint();
}
public void blue() {
graphics.setPaint(Color.blue);
repaint();
}
public void green() {
graphics.setPaint(Color.green);
repaint();
}
}
我将它添加到 JPanel。绘图本身工作正常。现在我想实现一个撤销方法。我以为我可以将当前的 graphics2D 对象复制到备份变量中，然后单击撤消按钮，我会将当前对象替换为备份对象。不幸的是，这没有用。
我尝试了以下方法：
在 mousePressed 方法中，我将图形的当前值分配给备份变量。
addMouseListener(new MouseAdapter() {
@Override
public void mousePressed(MouseEvent e) {
graphicsBackup = graphics.create();
oldX = e.getX();
oldY = e.getY();
}
});
在 undo 方法中，我尝试将备份变量的引用分配给原始对象。
public void undo() {
graphics = graphicsBackup;
repaint();
}
在我的第二次尝试中，我使用了 AffineTransform 对象。我在keyPressed方法中调用getTransform获取当前状态，然后在undo方法中调用setTransform。那也没有用。你对它如何工作有什么建议吗？
解决方案：（为背景等添加了一些额外的方法）
class DrawPad extends JComponent {
private Image image;
private Image background;
private Graphics2D graphics;
private int currentX, currentY, oldX, oldY;
private final SizedStack<Image> undoStack = new SizedStack<>(12);
public DrawPad() {
setDoubleBuffered(false);
addMouseListener(new MouseAdapter() {
@Override
public void mousePressed(MouseEvent e) {
saveToStack(image);
oldX = e.getX();
oldY = e.getY();
}
});
addMouseMotionListener(new MouseMotionAdapter() {
@Override
public void mouseDragged(MouseEvent e) {
currentX = e.getX();
currentY = e.getY();
if (graphics != null) {
graphics.drawLine(oldX, oldY, currentX, currentY);
}
repaint();
oldX = currentX;
oldY = currentY;
}
});
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
if (image == null) {
image = createImage(getSize().width, getSize().height);
graphics = (Graphics2D) image.getGraphics();
graphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
clear();
}
g.drawImage(image, 0, 0, getWidth(), getHeight(), null);
}
public void clear() {
if (background != null) {
setImage(copyImage(background));
} else {
graphics.setPaint(Color.white);
graphics.fillRect(0, 0, getSize().width, getSize().height);
graphics.setPaint(Color.black);
}
repaint();
}
public void undo() {
if (undoStack.size() > 0) {
setImage(undoStack.pop());
}
}
private void setImage(Image img) {
graphics = (Graphics2D) img.getGraphics();
graphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
graphics.setPaint(Color.black);
image = img;
repaint();
}
public void setBackground(Image img) {
background = copyImage(img);
setImage(copyImage(img));
}
private BufferedImage copyImage(Image img) {
BufferedImage copyOfImage = new BufferedImage(getSize().width, getSize().height, BufferedImage.TYPE_INT_RGB);
Graphics g = copyOfImage.createGraphics();
g.drawImage(img, 0, 0, getWidth(), getHeight(), null);
return copyOfImage;
}
private void saveToStack(Image img) {
undoStack.push(copyImage(img));
}
public void red() {
graphics.setPaint(Color.red);
repaint();
}
public void black() {
graphics.setPaint(Color.black);
repaint();
}
public void magenta() {
graphics.setPaint(Color.magenta);
repaint();
}
public void blue() {
graphics.setPaint(Color.blue);
repaint();
}
public void green() {
graphics.setPaint(Color.green);
repaint();
}
}
大小堆栈：
public class SizedStack<T> extends Stack<T> {
private final int maxSize;
public SizedStack(int size) {
super();
this.maxSize = size;
}
@Override
public Object push(Object object) {
while (this.size() > maxSize) {
this.remove(0);
}
return super.push((T) object);
}
}
不久前我自己实现了一个绘图程序。这是我实现撤消/重做的方式：
我有两个堆栈。“撤消”堆栈和“重做”堆栈。每次用户画东西时，我都是这样做的：
比如用户要画一条线，我之前把当前图片存入栈将线应用到图像将。应用该行后，我再次将其保存到堆栈中。
当用户按下“撤消”时，我只需从“撤消”堆栈中弹出顶部图像，并将其绘制到屏幕上。然后我把它放在“重做”堆栈中。
当用户按下“重做”时，“重做”堆栈中的顶部图像被弹出并应用于绘图区域，并放在“撤消”堆栈的顶部（相反的操作）。
编辑：为了将图像推入堆栈（堆栈中的所有对象都不是对同一对象的引用），您需要先将图像复制到新图像。这样的事情（可能在细节上不准确）：
void saveToStack(BufferedImage img){ // makes a copy of img and puts on stack.
BufferedImage imageForStack = new BufferedImage(img.getWidth(), img.getHeight(), img.getType());
Graphics2D g2d = imageForStack.createGraphics();
g2d.drawImage(img, 0, 0, null);
undoStack.push(imageForStack);
}
希望这可以帮助。