如何制作半圆角边框？

Question

我有一个 RoundPanel 类，它扩展了 JPanel 并提供圆形外观。

JPanel user_icon = new RoundPanel(8);
user_icon.setBackground(Color.decode("#363b41"));
user_icon.setBorder(null);
user_icon.setBounds(160, 135, 40, 46);
container.add(user_icon);
user_icon.setLayout(null);

public class RoundPanel extends JPanel {

    private static final long serialVersionUID = 1L;
    private Shape shape;
    
    public RoundPanel(int size) {
        setOpaque(false);
    }
    
    protected void paintComponent(Graphics g) {
         g.setColor(getBackground());
         g.fillRoundRect(0, 0, getWidth()-1, getHeight()-1, 8, 8);
         super.paintComponent(g);
    }
    
    protected void paintBorder(Graphics g) {
         g.drawRoundRect(0, 0, getWidth()-1, getHeight()-1, 8, 8);
    }
    
    public boolean contains(int x, int y) {
         if (shape == null || !shape.getBounds().equals(getBounds())) {
             shape = new RoundRectangle2D.Float(0, 0, getWidth()-1, getHeight()-1, 8, 8);
         }
         return shape.contains(x, y);
    }
}

想要将其修改为仅将左角圆化。 （一半圆形，一半无）

Answer 1

我强烈建议您花时间阅读使用几何，实际上，我还建议您花时间阅读整个2D 图形轨迹。

没有一个示例/解决方案能够 100% 满足您的要求，您需要准备好投入时间尝试不同的解决方案并根据您的需求调整您喜欢的解决方案，这是优秀开发人员的标志。

因此，通过一些实验（以及大量阅读我之前的答案），我能够想出......

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.Path2D;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Main {

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

    public Main() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame("Test");
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    protected class TestPane extends JPanel {

        @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);

            g2d.setColor(Color.RED);
            RoundedShape shape = new RoundedShape(
                    20,
                    100, 100,
                    RoundedShape.Corner.TOP_LEFT,
                    RoundedShape.Corner.TOP_RIGHT,
                    RoundedShape.Corner.BOTTOM_RIGHT,
                    RoundedShape.Corner.BOTTOM_LEFT
            );
            g2d.translate(10, 10);
            g2d.draw(shape);

            g2d.dispose();
        }
    }

    public class RoundedShape extends Path2D.Double {

        enum Corner {
            TOP_LEFT, TOP_RIGHT, BOTTOM_LEFT, BOTTOM_RIGHT;
        }

        private double radius = 20;
        private Set<Corner> corners;
        private Dimension size;

        public RoundedShape(double radius, int width, int height, Corner... corners) {
            this.corners = new HashSet(Arrays.asList(corners));
            this.radius = radius;
            this.size = new Dimension(width, height);

            build();
        }

        protected void build() {
            moveTo(0, 0);
            if (corners.contains(Corner.TOP_LEFT)) {
                moveTo(0, radius);
                curveTo(0, radius, 0, 0, radius, 0);
            }
            if (corners.contains(Corner.TOP_RIGHT)) {
                lineTo(size.width - radius, 0);
                // Draw the curve here
                curveTo(size.width - radius, 0,
                        size.height, 0,
                        size.width, radius);
            } else {
                lineTo(size.width, 0);
            }
            if (corners.contains(Corner.BOTTOM_RIGHT)) {
                lineTo(size.width, size.height - radius);
                // Draw the curve here
                curveTo(size.width, size.height - radius,
                        size.height, size.width,
                        size.width - radius, size.height);
            } else {
                lineTo(size.width, size.height);
            }
            if (corners.contains(Corner.BOTTOM_LEFT)) {
                lineTo(radius, size.height);
                // Draw the curve here
                curveTo(radius, size.height,
                        0, size.height,
                        0, size.height - radius);
            } else {
                lineTo(0, size.height);
            }
            closePath();
        }
    }
}

我建议看看使用鼠标拖动在 Java 中绘制曲线，因为使用贝塞尔曲线总是让我感到困惑。