如何只在某个区域绘制东西？

Question

我正在制作一款塔防游戏，我将有一些标记，根据它们的放置位置，它们有可能被绘制到游戏网格之外。我一直在我的游戏类的一个画布上绘制所有东西，我想知道是否有一种方法可以只在设定的区域（在本例中是我的游戏网格）中绘制某些东西。

为了更好地解释它，如果要在游戏网格的边缘画一个圆圈，就像要切断的悬垂一样。

我的 gui 是什么样子的：

Answer 1

一种方法可能是调整Graphics 上下文的剪辑。我个人不喜欢弄乱剪辑，因为如果你不小心，它可能会严重影响你。

查看Clipping the Drawing Region了解更多详情

剪辑示例

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.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestClip {

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

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

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

    public class TestPane extends JPanel {

        private BufferedImage img;

        public TestPane() {
            setBackground(Color.BLACK);
            try {
                img = ImageIO.read(new File("Lurk.png"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setColor(Color.RED);
            g2d.drawRect(100, 100, 200, 200);
            g2d.setClip(101, 101, 199, 199);
            g2d.drawImage(img, 300 - (img.getWidth() / 2), (getHeight() - img.getHeight()) / 2, this);
            g2d.dispose();
        }
    }

}

另一种方法可能是生成一个透明的BufferedImage 作为图层，您可以确保将绘画限制为正确的大小，将这些附加元素绘制到其上，然后绘制生成的BufferedImage地图上方

图层示例

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.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestClip {

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

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

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

    public class TestPane extends JPanel {

        private BufferedImage img;
        private BufferedImage layer;

        public TestPane() {
            setBackground(Color.BLACK);
            try {
                img = ImageIO.read(new File("Lurk.png"));
                layer = new BufferedImage(199, 199, BufferedImage.TYPE_INT_ARGB);
                Graphics2D g2d = layer.createGraphics();
                g2d.drawImage(img, 
                        layer.getWidth() - (img.getWidth() / 2), 
                        (layer.getHeight() - img.getHeight()) / 2, 
                        this);
                g2d.dispose();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(400, 400);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setColor(Color.RED);
            g2d.drawRect(100, 100, 200, 200);
            g2d.drawImage(layer, 101, 101, this);
//            g2d.setClip(101, 101, 199, 199);
//            g2d.drawImage(img, 300 - (img.getWidth() / 2), (getHeight() - img.getHeight()) / 2, this);
            g2d.dispose();
        }
    }

}