java - 在玩家身后创建一条血迹

Question

我目前正在开发一个简单的自上而下的射击游戏。该物体是一个在屏幕上滑动的球，我试图制造一种湿拖的效果。

我正在使用 Java Swing 和内部默认的 Graphics2d 库。

这就是我所拥有的:

这是我的目标:

我需要知道如何制作一条能够改变尾端 alpha 的曲线。我在网上搜索过，但只能找到非动态解决方案。 (当玩家在屏幕上移动时，尾部需要更新。)

Answer 1

一个简单的解决方案可能是将每个点简单地添加到玩家移动之前的点的列表中。

然后，您只需迭代此列表，然后简单地使用诸如 Graphics#drawLine 或什至 GeneralPath 之类的东西来呈现“拖动”线，例如。 .

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.Point;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.geom.Ellipse2D;
import java.awt.geom.GeneralPath;
import java.util.ArrayList;
import java.util.List;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Drag {

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

    public Drag() {
        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 List<Point> points;
        private Point pos;

        private int diametere = 10;

        public TestPane() {
            points = new ArrayList<>(25);

            InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0), "left");
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0), "right");
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0), "up");
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0), "down");

            ActionMap am = getActionMap();
            am.put("left", new MoveAction(-5, 0));
            am.put("right", new MoveAction(5, 0));
            am.put("up", new MoveAction(0, -5));
            am.put("down", new MoveAction(0, 5));

            pos = new Point(100 - (diametere / 2), 100 - (diametere / 2));
        }

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

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            if (points.size() > 1) {
                g2d.setColor(Color.RED);
                GeneralPath path = new GeneralPath();
                boolean started = false;
                System.out.println("----");
                for (Point p : points) {
                    if (started) {
                        System.out.println(p);
                        path.lineTo(p.x, p.y);
                    } else {
                        path.moveTo(p.x, p.y);
                        started = true;
                    }
                }
                g2d.draw(path);
            }
            int radius = (int) (diametere / 2d);
            g2d.setColor(Color.GREEN);
            g2d.draw(new Ellipse2D.Double(pos.x - radius, pos.y - radius, diametere, diametere));
            g2d.dispose();
        }

        protected void moveBy(int xDelta, int yDelta) {

            if (pos.x + xDelta < 0) {

                xDelta = 0;
                pos.x = 0;

            } else if (pos.x + xDelta + diametere > getWidth()) {

                xDelta = 0;
                pos.x = getWidth() - diametere;

            }
            if (pos.y + yDelta < 0) {

                yDelta = 0;
                pos.y = 0;

            } else if (pos.y + yDelta + diametere > getHeight()) {

                yDelta = 0;
                pos.y = getWidth() - diametere;

            }

            points.add(new Point(pos));

            pos.x += xDelta;
            pos.y += yDelta;

            repaint();

        }

        public class MoveAction extends AbstractAction {

            private int xDelta;
            private int yDelta;

            public MoveAction(int xDelta, int yDelta) {
                this.xDelta = xDelta;
                this.yDelta = yDelta;
            }

            @Override
            public void actionPerformed(ActionEvent e) {
                moveBy(xDelta, yDelta);
            }

        }
    }

}