5

我想创建一个带有圆角的自定义边框。

代码 - 

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Component;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Insets;
import java.awt.RenderingHints;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.border.AbstractBorder;

class JRoundedCornerBorder extends AbstractBorder 
{   
    private static final long serialVersionUID = 7644739936531926341L;
    private static final int THICKNESS = 5;

    JRoundedCornerBorder()
    {
        super();
    }

    @Override
    public void paintBorder(Component c, Graphics g, int x, int y, int width, int height) 
    {
        Graphics2D g2 = (Graphics2D)g.create();

        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        if(c.hasFocus())
        {
            g2.setColor(Color.BLUE);
        }
        else
        {
            g2.setColor(Color.BLACK);
        }
        g2.setStroke(new BasicStroke(THICKNESS, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
        g2.drawRect(x, y, width - 1, height - 1);

        g2.dispose();
    }

    @Override
    public Insets getBorderInsets(Component c) 
    {
        return new Insets(THICKNESS, THICKNESS, THICKNESS, THICKNESS);
    }

    @Override
    public Insets getBorderInsets(Component c, Insets insets) 
    {
        insets.left = insets.top = insets.right = insets.bottom = THICKNESS;
        return insets;
    }

    public static void main(String[] args) 
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run() 
            {
                final JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new FlowLayout());

                // Add button with custom border
                final JButton button = new JButton("Hello");
                button.setBorder(new JRoundedCornerBorder());
                frame.add(button);

                // Add button without custom border
                frame.add(new JButton("Goodbye"));

                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}

结果 -

在此处输入图像描述

如您所见，Graphics.drawRect完全忽略了BasicStroke.CAP_ROUNDandBasicStroke.JOIN_ROUND属性。为什么？

4

2 回答 2

7

如学习 Java 2D，第 1 部分所述：

java.awt.BasicStroke.CAP_ROUND：这会形成一个以端点为中心的圆形帽，其直径为笔宽。

关键词是“居中”。我相信总是这样，当用粗笔画时，Java2D 将沿着起始坐标和结束坐标处像素中心之间的假设的无限细线将线的粗细居中。例如，当绘制一条 7 像素粗的垂直蓝线时，Java2D 在正在绘制的假设线段的每一侧绘制 3 个像素。

在您的示例中，厚度为 5 个像素。您需要偏移坐标才能在图形剪辑中完全绘制笔触。通过移动 2 个像素（或THICKNESS/2），圆角变得可见：

移动 2 个像素后的 GUI 屏幕截图

//...
        g2.setStroke(new BasicStroke(THICKNESS, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
        g2.drawRect(x + THICKNESS/2, y + THICKNESS/2, width - 2*(THICKNESS/2) - 1, height - 2*(THICKNESS/2) - 1);

        g2.dispose();
    }

    @Override
    public Insets getBorderInsets(Component c) {
        return new Insets(THICKNESS + THICKNESS/2, THICKNESS + THICKNESS/2, THICKNESS + THICKNESS/2, THICKNESS + THICKNESS/2);
    }
//...
于 2011-12-06T14:54:28.700 回答
5

问题是偏移量：你有效地切断了中间的边界，所以角落看起来不是圆的。考虑到（这里只针对偏移，也需要调整宽度）

   g2.drawRect(x + thickness/2, y + thickness/2, 
       width - 1 - thickness, height - 1 - thickness);

编辑

修复了草率的像素计数:-)

于 2011-12-06T14:52:48.243 回答