围绕其中心旋转移动的形状 [英] Rotate a moving shape around its center

问题描述

我在Java中制作2D游戏，玩家通过障碍物引导多边形。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，但由于它经常被平移，所以它围绕移动旋转。尝试将其转换回原始中心，旋转它并将其翻译回来并不起作用。如何获得形状的中心？

I'm making a 2D game in Java where the player guides a polygon through obstacles. The polygon moves up and down and the game world scrolls left and right. I need the polygon to rotate around its center, but since it is constantly being translated the point it is being rotated around moves. Trying to translate it back to the original center, rotate it, and translate it back doesn't work. How do I get the center of the shape?

这是我在2ms计时器上的运动计算：

Here are my motion calculations on a 2ms timer:

@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：

And here is my paintComponent method:

@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）是其中心屏幕。

where (xPos, yPos) are the center of the screen.

推荐答案

转换是（通常）复合

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，您正在翻译原文图形上下文和副本。在此上下文中， copy 不受原件的影响，原件不受副本的影响，但是，原始上下文是共享资源，因为您不重置翻译，每次都会继续获得翻译的上下文（复合）。

In your above code, you are translating both the original Graphics context and the copy. In this context, copy won't be affected by the original and the original won't be affected by the copy, BUT, the original context is a shared resource and since you don't reset the translation, you will continue to get a translated context each time (compounding).

As根据一般经验法则，对副本进行所有转换并在完成后将其丢弃。

As a general rule of thumb, do ALL transformations on a copy and dispose of it when you're done.

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();

这基本上将对象的位置转换为玩家的位置，然后围绕中心旋转对象对象

This basically translates the position of the object to the player's position and then rotates the object about the centre of the object

你也可以应用一个转换，创建该上下文的副本并应用另一个转换，这将变得复杂（所以你可以翻译一个上下文，复制它，然后旋转副本，第一个翻译仍将应用于副本）

You could, also, apply one transformation, create a copy of that context and apply another transformation, which would become compounded (so you could translate one context, copy it, and then rotate the copy and the first translation would still applied to the copy)

这个令人难以置信的简单示例演示了两个基本示例......

This incredible simple example demonstrates two basic example...

1. 使用图形上下文和 AffineTransform 翻译和旋转玩家对象（关于它的中心点）


2. 使用一个 Path2D 生成一个转换后的形状（这个例子生成两个对象，但你可以使用一个 AffineTransform 翻译和旋转并申请一次）。

1. Using the Graphics context and a AffineTransform to translate and rotate the player object (about it's centre point)
2. Using a Path2D to generate a transformed shape (this example makes two objects, but you could use a single AffineTransform translated and rotated and apply it once).

在这两种情况下，他们都不要不会影响原始形状

In both cases, they don't affect the original shape

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();
        }

    }
}

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