围绕其中心旋转移动的形状

Question

我正在 Java 制作一款 2D 游戏，玩家可以在其中引导多边形穿过障碍物。多边形上下移动，游戏世界左右滚动。我需要多边形围绕其中心旋转，但由于它不断被平移，因此它围绕移动旋转的点。试图将它平移回原来的中心，旋转它，然后再平移回去是行不通的。如何获得形状的中心？

这是我在 2ms 计时器上的运动计算：

@Override
public void actionPerformed(ActionEvent e) {

    double theta = angleRad+90;
    if (up == true) {
        if (accelerating == false) {
            time2 = 0;
            moveX0 = moveX;
            moveY0 = moveY;
            accelerating = true;
        }
        time1++;
        double t = time1/500;
        if (accCount % 10 == 0) {
            DronePilot.velocity++;
        }
        moveX = moveX0 + velX*Math.cos(theta)*t;
        moveY = moveY0 + velY*Math.sin(theta)*t-(1/2d)*g*Math.pow(t, 2);
        velX = (DronePilot.velocity)*Math.cos(theta);
        velY = (DronePilot.velocity)*Math.sin(theta)-g*(t);
        accCount++;
    } else if (up == false){
        if (accelerating == true) {
            time1 = 0;
            moveX0 = moveX;
            moveY0 = moveY;
            accelerating = false;
        }
        time2++;
        double t = time2/500;
        moveX = moveX0 + velX*Math.cos(theta)*t;
        moveY = moveY0 + velY*Math.sin(theta)*t-(1/2d)*g*Math.pow(t, 2);
        accCount = 0;
    } if (left == true) {
        angleCount++;
        if (angleCount % 2 == 0) {
            angleDeg++;
        }
        angleRad = Math.toRadians(angleDeg);
    } else if (right == true) {
        angleCount--;
        if (angleCount % 2 == 0) {
            angleDeg--;
        }
        angleRad = Math.toRadians(angleDeg);
    }
    repaint();
}
}

这是我的 paintComponent 方法：

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2D = (Graphics2D)g;

    Graphics g2 = g.create();
    Graphics2D copy = (Graphics2D)g2;




    copy.rotate(-angleRad, xPos, yPos);

    copy.translate(0, -moveY);

    g2D.translate(-moveX, 0);

    copy.draw(player.shape);

    for (Rectangle2D.Double r: DronePilot.rocksFloorArray) {
        g2D.draw(r);
    }
    for (Rectangle2D.Double r: DronePilot.rocksCeilArray) {
        g2D.draw(r);
    }
    for (Rectangle2D.Double r: DronePilot.roomsArray) {
        g2D.draw(r);
    }
}

其中 (xPos, yPos) 是屏幕的中心。

Answer 1

在 openGL 中，我们使用 pushMatrix() 和 popMatrix() 保存变换状态。这里它们的等价物是 Graphics.create() 和 Graphics.dispose()

Graphics g1 = g.create();
//do transformations
g1.dispose();

Graphics g2 = g.create();
//do other stuff
g2.dispose();

Answer 2

转换（通常）是复合的

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2D = (Graphics2D)g;

    Graphics g2 = g.create();
    Graphics2D copy = (Graphics2D)g2;

    copy.rotate(-angleRad, xPos, yPos);
    copy.translate(0, -moveY);

    g2D.translate(-moveX, 0);

    copy.draw(player.shape);
    for (Rectangle2D.Double r: DronePilot.rocksFloorArray) {
        g2D.draw(r);
    }
    for (Rectangle2D.Double r: DronePilot.rocksCeilArray) {
        g2D.draw(r);
    }
    for (Rectangle2D.Double r: DronePilot.roomsArray) {
        g2D.draw(r);
    }
}

在上面的代码中，您同时翻译了原始 Graphics 上下文和 copy。在这种情况下，copy 不会受到原件的影响，原件也不会受到 copy 的影响，但是，原件上下文是共享资源，并且由于您没有重置翻译，您每次都会继续获得翻译的上下文（复合）。

作为一般经验法则，对副本进行所有转换并在完成后将其丢弃。

例如...

Graphics2D g2d = (Graphics2D)g.create();
AffineTransform at = AffineTransform.getTranslateInstance(playerPoint.x, playerPoint.y);
at.rotate(Math.toRadians(angle), player.getBounds2D().getCenterX(), player.getBounds2D().getCenterY());
g2d.setTransform(at);
g2d.setColor(Color.RED);
g2d.fill(player);
g2d.setColor(Color.BLACK);
g2d.draw(player);
g2d.dispose();

这基本上是将对象的位置转换为玩家的位置，然后围绕对象的中心旋转对象

您还可以应用一个转换，创建该上下文的副本并应用另一个转换，这将变得复合（因此您可以 translate 一个上下文，复制它，然后 rotate 副本和第一个翻译仍适用于副本）

这个令人难以置信的简单示例演示了两个基本示例...

使用 Graphics 上下文和 AffineTransform 平移和旋转玩家对象（围绕其中心点）
使用 Path2D 生成变换后的形状（此示例生成两个对象，但您可以使用单个 AffineTransform 进行平移和旋转并应用一次）。

在这两种情况下，它们都不会影响原始形状

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.Rectangle;
import java.awt.Shape;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;
import java.awt.geom.Path2D;
import java.awt.geom.Rectangle2D;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class Test {

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

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

    public class TestPane extends JPanel {

        private Shape player;
        private Point playerPoint;
        private float angle;
        private float deltaZ = 1.0f;

        private int deltaX, deltaY;

        public TestPane() {
            player = new Rectangle(0, 0, 20, 20);
            playerPoint = new Point(80, 80);
            Random rnd = new Random();
            deltaX = 1;
            deltaY = -1;

            Timer timer = new Timer(5, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    playerPoint.x += deltaX;
                    playerPoint.y += deltaY;

                    Shape rotatedPlayer = rotatedAndTranslatedPlayer();
                    Rectangle2D bounds = rotatedPlayer.getBounds2D();
                    if (bounds.getX() < 0.0) {
                        playerPoint.x = (int)(bounds.getX() * -1);
                        deltaX *= -1;
                    } else if (bounds.getX() + bounds.getWidth() >= getWidth()) {
                        playerPoint.x = getWidth() - (int)bounds.getWidth();
                        deltaX *= -1;
                    }
                    if (bounds.getY() < 0) {
                        playerPoint.y = 0;
                        deltaY *= -1;
                    } else if (bounds.getY() + bounds.getHeight() > getHeight()) {
                        playerPoint.y = getHeight() - (int)bounds.getHeight();
                        deltaY *= -1;
                    }
                    angle += deltaZ;
                    repaint();
                }
            });
            timer.start();
        }

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

        protected Shape rotatedAndTranslatedPlayer() {
            Path2D.Double rotated = new Path2D.Double(player,  AffineTransform.getRotateInstance(
                    Math.toRadians(angle),
                    player.getBounds2D().getCenterX(), 
                    player.getBounds2D().getCenterY()));
            return new Path2D.Double(rotated, AffineTransform.getTranslateInstance(playerPoint.x, playerPoint.y));            
        }

        // Simply paints the "area" that the player takes up when it's rotated and
        // translated
        protected void paintAutoTranslatedShape(Graphics2D g2d) {
            g2d.setColor(Color.DARK_GRAY);
            g2d.fill(rotatedAndTranslatedPlayer().getBounds2D());
        }

        // Uses a AffineTransform to translate and rotate the player
        protected void paintPlayer(Graphics2D g2d) {
            AffineTransform at = AffineTransform.getTranslateInstance(playerPoint.x, playerPoint.y);
            at.rotate(Math.toRadians(angle), player.getBounds2D().getCenterX(), player.getBounds2D().getCenterY());
            g2d.setTransform(at);
            g2d.setColor(Color.RED);
            g2d.fill(player);
            g2d.setColor(Color.BLACK);
            g2d.draw(player);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            paintAutoTranslatedShape(g2d);
            g2d.dispose();
            g2d = (Graphics2D) g.create();
            paintPlayer(g2d);
            g2d.dispose();
        }

    }
}

围绕其中心旋转移动的形状

Rotate a moving shape around its center

java

rotation

graphics2d

affinetransform