圆圈中的圆圈渐渐消失，创造了一个目标

Question

我想创建一个图形，其中圆圈重叠并且颜色渐渐淡出，圆圈之间应该有一个白色空间，类似于：

这是我有多远：

import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;
import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;

class Circles extends JPanel implements MouseListener {


    public void mouseReleased(MouseEvent event) {

    }
    public void mousePressed(MouseEvent event) {

    }
    public void mouseClicked(MouseEvent event) {

    }
    public void mouseEntered(MouseEvent event) {}
    public void mouseExited(MouseEvent event) {}


    public Circles() {
        addMouseListener(this);
    }


    public void paint(Graphics g) {
        g.setColor(Color.white);
        int w = getWidth();
        int h = getHeight();
        g.fillRect(0, 0, w, h);


        Graphics2D g2 = (Graphics2D) g;

        for (int i = 0; i < 20; i++) {
            if (i % 2 == 0) {
                Color c = new Color(255 - i * 10, 255 - i * 10, 255 - i * 10);
                g2.setColor(c);
            } else {
                g2.setColor(Color.white);
            }

            g2.fillOval((5 * i), (5 * i), (w - 10) * i, (h - 10) * i);
        }
    }

    public static void main(String[] args) {
        Frame w = new Frame();
        w.setVisible(true);
    }
}

框：

import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;


public class Frame extends JFrame {
    Circles myPanel;

    public static void main(String[] args) {
        Frame w = new Frame();
        w.setVisible(true);
    }

    public Frame() {
        setTitle("In-class Test 1: Starting Code");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(500, 220);
        setLocation(300, 300);
        myPanel = new Circles();
        add(myPanel);
    }
}

Answer 1

有很多方法可以实现这一目标，但首先，首先要覆盖paintComponent而不是paint。

其次，你需要某种循环来扩展每次迭代时圆的半径。

第三，你需要一个简单的int值作为一个alpha值，从255开始减少到你想要的最微弱的alpha级别，可能是64个例子。

在循环的每次迭代中，您将需要增加半径值并相应地减小alpha值。然后，您只需要使用RGB＆amp;创建一个新的Color对象。你需要的alpha值

查看2D Graphics了解详情

更新了示例...

import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.Ellipse2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class FadingCircles {

    public static void main(String[] args) {
        new FadingCircles();
    }

    public FadingCircles() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        });
    }

    public static class TestPane extends JPanel {

        public static final int CIRCLE_COUNT = 10;

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();

            g2d.setRenderingHint(RenderingHints.KEY_ALPHA_INTERPOLATION, RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY);
            g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            g2d.setRenderingHint(RenderingHints.KEY_COLOR_RENDERING, RenderingHints.VALUE_COLOR_RENDER_QUALITY);
            g2d.setRenderingHint(RenderingHints.KEY_DITHERING, RenderingHints.VALUE_DITHER_ENABLE);
            g2d.setRenderingHint(RenderingHints.KEY_FRACTIONALMETRICS, RenderingHints.VALUE_FRACTIONALMETRICS_ON);
            g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
            g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
            g2d.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL, RenderingHints.VALUE_STROKE_PURE);

            int maxRadius = Math.min(getWidth(), getHeight());
            int alpha = 255;
            int range = 255 - 32;
            g2d.setStroke(new BasicStroke(6, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));

            for (int index = 0; index < CIRCLE_COUNT; index++) {
                float progress = (float) index / (float) CIRCLE_COUNT;
                alpha = 255 - Math.round(range * progress);
                Color color = new Color(0, 0, 0, alpha);
                g2d.setColor(color);

                int radius = Math.round(maxRadius * progress);
                int x = (getWidth() - radius) / 2;
                int y = (getHeight() - radius) / 2;

                g2d.draw(new Ellipse2D.Float(x, y, radius, radius));
            }
            g2d.dispose();
        }
    }
}

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