在Java中绘制带有尖角的边界路径 [英] Drawing a bordered path with sharp corners in Java

问题描述

我正在开发在地图上显示GPS轨迹的应用程序。我想将轨迹绘制为任意厚度的彩色路径。我发现 GeneralPath 类似乎可以满足我的要求。但是，我希望彩色路径也具有黑色边框。我找不到有关如何在路径上添加边框的任何信息，所以我想出了一个快速的解决方案，即先绘制一条粗的黑色路径，然后再在顶部绘制一条细的彩色路径。

I am working on an application that displays GPS tracks on a map. I want to draw the track as a colored path of arbitrary thickness. I found the GeneralPath class which seems to do just what I want. However, I want the colored path to also have a black border. I couldn't find anything about how to add a border to a path, so I came up with a quick hacky solution of drawing a thick black path first, and then drawing a thin colored path on top.

SSCCE：

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.GeneralPath;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class PathBorder {
    private JFrame frame;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    PathBorder window = new PathBorder();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public PathBorder() {
        initialize();
    }

    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 450, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panel = new JPanel() {
            protected void paintComponent(Graphics g) {
                GeneralPath path;
                Graphics2D g2d = (Graphics2D) g;
                g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                        RenderingHints.VALUE_ANTIALIAS_ON);
                g2d.setStroke(new BasicStroke(5.5f));
                g2d.setColor(Color.BLACK);
                path = new GeneralPath();
                path.moveTo(0, 0);
                path.lineTo(100, 100);
                path.lineTo(200, 100);
                path.lineTo(100, 80);
                g2d.draw(path);
                g2d.setStroke(new BasicStroke(3));
                g2d.setColor(Color.YELLOW);
                g2d.draw(path);
            }
        };
        frame.setBackground(Color.CYAN);
        frame.add(panel);
    }
}

下面是一张图片（摘自SSCCE）突出我的问题。请参阅下面的红色圆圈，请注意外部边界中是否有缝隙。我希望填补这个空白，以便边界是连续的。

Here is a pic (taken from the SSCCE) to highlight my problem. See the red circle below, notice how the outside border has a gap in it. I want that gap to be filled in so the border is continuous.

以下是我的应用中一些真实曲目的实际屏幕截图：

Here are some actual screenshots from my app of a real track:

如果您仔细看一下发夹在曲目的右下角转动，您会看到边框短暂丢失了……下面的详细图片使它变得更加清晰。

If you look closely at the sharp hairpin turn in the lower right of the track, you'll see that the border gets lost briefly... the detailed pic below makes it more clear.

我不确定如何解决此问题，但我愿意接受建议，要么遵循 GeneralPath 策略，要么完全使用其他想法。

I am not sure exactly how to fix this, but I'm open to suggestions, either keeping with the GeneralPath strategy, or using a different idea entirely.

推荐答案

使用 cap 和 join 参数获得更好的效果。例如。

Experiment with the cap and join parameters for a better effect. E.G.

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.geom.GeneralPath;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class PathBorder {

    private JFrame frame;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            public void run() {
                try {
                    PathBorder window = new PathBorder();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public PathBorder() {
        initialize();
    }

    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 450, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panel = new JPanel() {

            GeneralPath path;

            protected void paintComponent(Graphics g) {
                Graphics2D g2d = (Graphics2D) g;
                g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                        RenderingHints.VALUE_ANTIALIAS_ON);
                BasicStroke s = new BasicStroke(
                        5.5f, 
                        BasicStroke.CAP_ROUND, 
                        BasicStroke.JOIN_ROUND);
                g2d.setStroke(s);
                g2d.setColor(Color.BLACK);
                if (path==null) {
                    path = new GeneralPath();
                    path.moveTo(0, 0);
                    path.lineTo(100, 100);
                    path.lineTo(200, 100);
                    path.lineTo(100, 80);
                }
                g2d.draw(path);
                g2d.setStroke(new BasicStroke(3));
                g2d.setColor(Color.YELLOW);
                g2d.draw(path);
            }
        };
        frame.setBackground(Color.CYAN);
        frame.add(panel);
    }
}

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