用户界面- Java Graphics2D擦除到alpha背景

Question

我正在制作一个应用程序，该应用程序有一个绘图板，您可以用鼠标绘制，它在BUfferedImage中绘制标签的顶部。我现在要实现的是一个橡皮擦，问题是我找不到任何地方帮助使橡皮擦clearRect()到alpha背景。(我不能有一个定义的颜色背景，因为用户可以改变背景为任何他想要的图像)。总结:

• 如何用alpha像素擦除/覆盖Graphics2D像素?我发现的方法是使用clearRect，但你需要指定一个背景颜色。

下面是我的DrawBoard类，它包含了要绘制的所有内容。

public class DrawBoard extends JPanel implements MouseListener, MouseMotionListener{

public JLabel status;
private JLabel imgLabel; // this is where the drawing happens
public Point pstart, pfinish;
private List<Point> points = new ArrayList<Point>();
private List<BufferedImage> lines = new ArrayList<BufferedImage>();
private static final int BI_WIDTH = 1024;
private static final int BI_HEIGHT = 800;
private static int STROKESIZE = 7;
private BufferedImage bImage = new BufferedImage(BI_WIDTH, BI_HEIGHT,
        BufferedImage.TYPE_INT_ARGB);
public Color currentColor;
public static boolean eraser = false;
private int xX1, yY1;
public DrawBoard(){  
   Graphics2D g2d = bImage.createGraphics();
   g2d.dispose();
    Dimension size = getPreferredSize();
    size.setSize(1024,800); //w, h
    setPreferredSize(size);
    //status =  new JLabel("default");
    //add(status, BorderLayout.SOUTH);
    addMouseListener(this);
    addMouseMotionListener(this);  

     imgLabel = new JLabel(new ImageIcon(bImage)) {
     @Override
     protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        paintInLabel(g);
     }
   };
     imgLabel.setOpaque(false);
     setOpaque(false);
      add(imgLabel, BorderLayout.CENTER);
}
private void paintInLabel(Graphics g) {
  Graphics2D g2d = (Graphics2D) g;
  g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
  g2d.setColor(getColor()); // this colour is when mouse is pressed
  g2d.setStroke(new BasicStroke(STROKESIZE));
  if (points.size() < 2) {
     return;
  }
  for (int i = 1; i < points.size(); i++) {
     int x1 = points.get(i - 1).x;
     int y1 = points.get(i - 1).y;
     int x2 = points.get(i).x;
     int y2 = points.get(i).y;
     g2d.drawLine(x1, y1, x2, y2);
  }
 }

@Override
public void mouseExited(MouseEvent e){  
}
@Override
public void mouseEntered(MouseEvent e){  
}
@Override
public void mouseMoved(MouseEvent e){   
}
// Where the drawing happens
@Override
public void mousePressed(MouseEvent e) {
    //status.setText("you pressed down the mouse");
    xX1 = e.getX();
    yY1 = e.getY();

        points.add(e.getPoint());
}
@Override
public void mouseDragged(MouseEvent e) {
  //status.setText("you draged the mouse");
        points.add(e.getPoint());
        imgLabel.repaint();
}
@Override
public void mouseReleased(MouseEvent e) {
    //status.setText("you release the mouse click");
    Graphics2D g2d = bImage.createGraphics();
    g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
    g2d.setColor(getColor()); // this is the final colour
    g2d.setStroke(new BasicStroke(STROKESIZE));

     if (points.size() >= 2) {
        for (int i = 1; i < points.size(); i++) {
           int x1 = points.get(i - 1).x;
           int y1 = points.get(i - 1).y;
           int x2 = points.get(i).x;
           int y2 = points.get(i).y;
           g2d.drawLine(x1, y1, x2, y2);
        }
     }
     g2d.dispose();
     points.clear();
     imgLabel.repaint();
}
// End of where the drawing happens
public void clearDrawBoard() {
}
private Color getColor() {
    return ColourToolbar.selectedColor;
}
private void setColor(Color col){
    this.currentColor = col;
}
@Override
public void mouseClicked(MouseEvent e) {
    //throw new UnsupportedOperationException("Not supported yet.");
}
}

Answer 1

您应该为Graphics2D设置自定义Composite，特别是alphaaccomposite。在绘制矩形之前清除。完成后，不要忘记将composite重置为默认值(SRC_OVER)，因为相同的Graphics对象将被重用来绘制其他组件。