Java-Rubber alpha function

Question

我目前正在制作一个绘画程序，并且目前正在实现一个橡胶工具（一种可以处理Alpha颜色的版本）。问题是，我无法通过mouseDragged事件绘制不可见的线条，因为它们只会出现在之前的绘画之上...

我已经在bImg上考虑了setRGB，但是它需要有mouseDragged支持，并且还要使线的粗细可变。任何人有任何想法吗？

编辑：为什么要投反对票？

Answer 1

您可以在某些条件下将图像转换为writeableraster，并使用getpixel（）和setpixel（）方法转换用户鼠标指针下方的颜色。

Answer 2

下降的现象可能与以下事实有关：您尝试达到的目标并不完全清楚[[what，而您已经尝试过how。

我假设您想在mouseDragged中的图像上画线。这些行应具有“橡胶” /“橡皮擦”的作用，删除一些以前绘制的像素，或者（当您说要具有alpha值时），也许不

removing

它们，而只是使它们更加苍白。不能使用setRGB手动更改像素值，因为这种橡胶效果应该具有一定的[[thickness，您可能需要在调用graphics.setStroke(new BasicStroke(thickness))之前设置graphics.draw(rubberLine)来选择。 如果这都是正确的，那么您可能必须使用http://docs.oracle.com/javase/6/docs/api/java/awt/Graphics2D.html#setComposite%28java.awt.Composite%29设置适当的组合。特别是，您将必须设置AlphaComposite（http://docs.oracle.com/javase/6/docs/api/java/awt/AlphaComposite.html）。您可以尝试不同的方法，以实现不同的“橡胶效果”，具体取决于已擦除像素具有的alpha值，以及为“橡胶颜色”设置的alpha值。 编辑：一个例子，...也许您应该更清楚地描述问题

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Line2D;
import java.awt.image.BufferedImage;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingUtilities;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class SimplePaint
{
    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                createAndShowGUI();
            }
        });
    }

    private static void createAndShowGUI()
    {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        PaintPanel paintPanel = new PaintPanel();

        f.getContentPane().setLayout(new BorderLayout());
        f.getContentPane().add(
            createControlPanel(paintPanel), BorderLayout.NORTH);
        f.getContentPane().add(paintPanel, BorderLayout.CENTER);

        f.setSize(500,500);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    static JPanel createControlPanel(final PaintPanel paintPanel)
    {
        JPanel controlPanel = new JPanel(new GridLayout(0,2));
        final JLabel label = new JLabel("Paint");
        final JSlider slider = new JSlider(0, 255, 0);
        slider.addChangeListener(new ChangeListener()
        {

            @Override
            public void stateChanged(ChangeEvent e)
            {
                int value = slider.getValue();
                if (value <= 0)
                {
                    label.setText("Paint");
                }
                else
                {
                    label.setText("Rubber alpha "+value);
                }
                paintPanel.setRubber(value);
            }
        });
        controlPanel.add(label);
        controlPanel.add(slider);
        return controlPanel;
    }
}



class PaintPanel extends JPanel implements MouseMotionListener
{
    private BufferedImage image;
    private Point previousPoint = new Point();
    private int rubberAlpha = -1;

    PaintPanel()
    {
        addMouseMotionListener(this);
    }

    void setRubber(int alpha)
    {
        this.rubberAlpha = alpha;
    }

    @Override
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        int w = getWidth();
        int h = getHeight();
        if (image == null)
        {
            image = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
            Graphics imageG = image.getGraphics();
            imageG.setColor(Color.WHITE);
            imageG.fillRect(0, 0, w, h);
            imageG.dispose();
        }
        else if (image.getWidth() != w || image.getHeight() != h)
        {
            BufferedImage newImage = 
                new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
            Graphics imageG = newImage.getGraphics();
            imageG.drawImage(image, 0, 0, null);
            imageG.dispose();
            image = newImage;
        }
        g.drawImage(image, 0, 0, null);
    }

    @Override
    public void mouseDragged(MouseEvent e)
    {
        if (image == null)
        {
            return;
        }

        Graphics2D g = (Graphics2D)image.getGraphics();
        g.setRenderingHint(
            RenderingHints.KEY_ANTIALIASING, 
            RenderingHints.VALUE_ANTIALIAS_ON);

        if (rubberAlpha > 0)
        {
            g.setColor(new Color(255,255,255,rubberAlpha));
            Line2D line = new Line2D.Double(previousPoint, e.getPoint());
            g.setStroke(new BasicStroke(20, 
                BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
            g.draw(line);
        }
        else
        {
            g.setColor(new Color(255,0,0,255));
            Line2D line = new Line2D.Double(previousPoint, e.getPoint());
            g.setStroke(new BasicStroke(20, 
                BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
            g.draw(line);
        }

        g.dispose();
        repaint();

        previousPoint = e.getPoint();
    }

    @Override
    public void mouseMoved(MouseEvent e)
    {
        previousPoint = e.getPoint();
    }
}

Answer 3