如何从AffineTransform派生的形状对象中“获取”特定点

As a self-project, I'm trying to make the game 'Asteroids'.

作为一个自我项目,我正试图制作游戏“小行星”。

Currently, I'm stuck on trying to figure out how to make it so the lasers fired from my ship appear from the tip of the ship. So far, I've tried experimenting with using the Shape object's .getBounds2D().getX() methods, but because getBounds2D() draws a rectangle around the polygon, the lasers end up appearing from the corner of the imaginary 'box' around my Polygon ship.

目前,我一直试图弄清楚如何制造它,以便从我的船上发射的激光从船的尖端出现。到目前为止,我已经尝试过使用Shape对象的.getBounds2D()。getX()方法,但是因为getBounds2D()在多边形周围绘制一个矩形,所以激光最终会出现在假想的“盒子”的角落周围我的多边形船。

Here's a gif of what I have so far.

这是我到目前为止的gif。

Is there a way to 'get' a specific point from a Shape object; where, in this case, that specific point is the tip of the ship.

有没有办法从Shape对象“获取”特定点;在这种情况下,该特定点是船的尖端。

Main Class:

public class AsteroidGame implements ActionListener, KeyListener{

    public static AsteroidGame game;
    public Renderer renderer;

    public boolean keyDown = false;
    public int playerAngle = 0;

    public boolean left = false;
    public boolean right = false;
    public boolean go = false;
    public boolean back = false;
    public boolean still = true;
    public double angle = 0;
    public int turnRight = 5;
    public int turnLeft = -5;

    public Shape transformed;

    public ArrayList<Laser> lasers;
    public ArrayList<Shape> transformedLasers;

    public final int WIDTH = 1400;
    public final int HEIGHT = 800;

    public Ship ship;
    public Rectangle shipHead;
    public Shape shipHeadTrans;
    public Point headPoint;


    public AffineTransform transform = new AffineTransform();
    public AffineTransform lasTransform = new AffineTransform();
    public AffineTransform headTransform = new AffineTransform();

    public AsteroidGame(){
        JFrame jframe = new JFrame();
        Timer timer = new Timer(20, this);
        renderer = new Renderer();

        jframe.add(renderer);
        jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jframe.setSize(WIDTH, HEIGHT);
        jframe.setVisible(true);
        jframe.addKeyListener(this);
        jframe.setResizable(false);

        int xPoints[] = {800, 780, 800, 820};
        int yPoints[] = {400, 460, 440, 460}; 

        //(800, 400) is the initial location of the 'tip' of the ship'.
        headPoint = new Point(800, 400);

        lasers = new ArrayList<Laser>();
        transformedLasers = new ArrayList<Shape>();

        ship = new Ship(xPoints, yPoints, 4, 0);
        transformed = transform.createTransformedShape(ship);

        shipHead = new Rectangle(headPoint);
        shipHeadTrans = transform.createTransformedShape(shipHead);
        //shipHeadTrans.getBounds2D().

        timer.start();

    }

    public void repaint(Graphics g){

        g.setColor(Color.BLACK);
        g.fillRect(0, 0, WIDTH, HEIGHT);

        Graphics2D g2d = (Graphics2D)g;

        //drawing the ship
        g2d.setColor(Color.WHITE);
        g2d.draw(transformed);

        //drawing lasers
        g2d.setColor(Color.RED);
        for (int i = 0; i < transformedLasers.size(); i++){
            System.out.println(i);
            g2d.draw(transformedLasers.get(i));
        }



    }



    public void actionPerformed(ActionEvent arg0) {
        // TODO Auto-generated method stub

        /*The for if and else if statements are just to send the ship
         * to the other side of the canvas if it ever leaves the screen
         */
        if (transformed.getBounds2D().getMinX() > WIDTH){
            double tempAng = ship.getAng();
            double diff = 90-tempAng;

            transform.rotate(Math.toRadians(diff), ship.getCenterX(), ship.getCenterY());
            transform.translate(0,WIDTH);
            transform.rotate(Math.toRadians(-diff), ship.getCenterX(), ship.getCenterY());

        }

        else if (transformed.getBounds2D().getX() < 0){
            double tempAng = ship.getAng();
            double diff = 90-tempAng;
            transform.rotate(Math.toRadians(diff), ship.getCenterX(), ship.getCenterY());
            transform.translate(0,-WIDTH);
            transform.rotate(Math.toRadians(-diff), ship.getCenterX(), ship.getCenterY());
        }

        else if (transformed.getBounds2D().getY() > HEIGHT){
            double tempAng = ship.getAng();
            double diff = 180-tempAng;
            transform.rotate(Math.toRadians(diff), ship.getCenterX(), ship.getCenterY());
            transform.translate(0,HEIGHT);
            transform.rotate(Math.toRadians(-diff), ship.getCenterX(), ship.getCenterY());
        }

        else if (transformed.getBounds2D().getY() < 0){
            double tempAng = ship.getAng();
            double diff = 180-tempAng;
            transform.rotate(Math.toRadians(diff), ship.getCenterX(), ship.getCenterY());
            transform.translate(0,-HEIGHT);
            transform.rotate(Math.toRadians(-diff), ship.getCenterX(), ship.getCenterY());
        }


        if (right){
            ship.right();
            //rotating the ship
            transform.rotate(Math.toRadians(turnRight), ship.getCenterX(), ship.getCenterY());
            //rotating the 'tip' of the ship.
            headTransform.rotate(Math.toRadians(turnRight), ship.getCenterX(), ship.getCenterY());
        }

        else if (left){
            ship.left(); 
            //rotating the ship
            transform.rotate(Math.toRadians(turnLeft), ship.getCenterX(), ship.getCenterY());
            //rotating the 'tip' of the ship
            headTransform.rotate(Math.toRadians(turnLeft), ship.getCenterX(), ship.getCenterY());
        }
        if (go){
            ship.go();
        }
        else if (back){
            ship.reverse();
        }

        //moving and shaping each individual laser that had been shot
        for (int i = 0; i < transformedLasers.size(); i++){
            lasers.get(i).move();

            lasTransform = new AffineTransform();
            lasTransform.rotate(Math.toRadians(lasers.get(i).getAng()), transformed.getBounds2D().getX(), transformed.getBounds2D().getY());
            transformedLasers.set(i, lasTransform.createTransformedShape(lasers.get(i)));

        }

        //moving the ship
        ship.move();

        //moving the 'tip'
        shipHead.y -= ship.getSpeed();

        transformed = transform.createTransformedShape(ship);
        shipHeadTrans = headTransform.createTransformedShape(shipHead);


        renderer.repaint();

    }

    //defining a new laser
    public void fireLaser(){
        Laser tempLaser = new Laser((int)transformed.getBounds2D().getX(), (int)transformed.getBounds2D().getY(), 5, 10, ship.getAng());
        lasers.add(tempLaser);

        lasTransform = new AffineTransform();
        lasTransform.rotate(Math.toRadians(ship.getAng()), transformed.getBounds2D().getX(), transformed.getBounds2D().getY());
        transformedLasers.add(lasTransform.createTransformedShape(tempLaser));

    }

    public static void main(String[] args){
        game = new AsteroidGame();
    }

    @Override
    public void keyPressed(KeyEvent e) {
        // TODO Auto-generated method stub
        if (e.getKeyCode() == KeyEvent.VK_RIGHT){
            right = true;
            keyDown = true;
        }else if (e.getKeyCode() == KeyEvent.VK_LEFT){
            left = true;
            keyDown = true;
        }

        else if (e.getKeyCode() == KeyEvent.VK_UP){
            go = true;
        }
        else if (e.getKeyCode() == KeyEvent.VK_DOWN){
            back = true;
        }

        //fire laser
        if (e.getKeyCode() == KeyEvent.VK_SPACE){
            fireLaser();
        }

    }

    @Override
    public void keyReleased(KeyEvent e) {
        // TODO Auto-generated method stub
        if (e.getKeyCode() == KeyEvent.VK_RIGHT){
            right = false;
        }
        if (e.getKeyCode() == KeyEvent.VK_LEFT){
            left = false;
        }
        if (e.getKeyCode() == KeyEvent.VK_UP){
            go = false;
        }
        if (e.getKeyCode() == KeyEvent.VK_DOWN){
            back = false;
        }
        still = true;
        keyDown = false;
    }

    @Override
    public void keyTyped(KeyEvent e) {
        // TODO Auto-generated method stub

    }

Ship Class (I don't think it's relevant though)

船级(我不认为它是相关的)

package asteroidGame;

import java.awt.Polygon;
import java.util.Arrays;

public class Ship extends Polygon{

    /**
     * 
     */
    private double currSpeed = 0;

    private static final long serialVersionUID = 1L;
    public double angle;
    public int[] midX;
    public int[] midY;

    public Ship(int[] x, int[] y, int points, double angle){
        super(x, y, points);
        midX = x;
        midY = y;

        this.angle= angle;
    }


    public void right(){
        angle += 5;
    }
    public void left(){
        angle -= 5;
    }

    public void move(){
        for (int i = 0; i < super.ypoints.length; i++){
            super.ypoints[i] -= currSpeed;
            //System.out.println(super.ypoints[i]);
            //System.out.println(super.xpoints[i]);
        }
        //System.out.println(Arrays.toString(super.ypoints));



    }
    public double getSpeed(){
        return currSpeed;
    }


    public void reverse(){
        if (currSpeed  > -15) currSpeed -= 0.2;
    }

    public void go(){
        if (currSpeed < 25) currSpeed += 0.5;

    }

    public int getCenterX(){
        return super.xpoints[2];
    }
    public int getCenterY(){
        return super.ypoints[2];
    }

    public double getAng(){
        return angle;
    }
    public void test(){
        for (int x = 0; x < super.ypoints.length; x++){
            super.ypoints[x] += 1000;
        }
    }

    /*
    public void decrement(){
        if(currSpeed == 0){}

        else if (currSpeed > 0 && currSpeed < 15){
            currSpeed -= 0.05;

        }
        else if (currSpeed < 0 && currSpeed > -15){
            currSpeed += 0.05;

        }
        System.out.println("losing speed");
    }
    */
}

Laser Class (I don't think this is relevant either, but here ya go.)

激光类(我不认为这也是相关的,但是在这里你去。)

package asteroidGame;

import java.awt.Color;
import java.awt.Rectangle;
import java.awt.geom.Rectangle2D;

public class Laser extends Rectangle{

    private double angle;

    public Laser(int x, int y , int width, int height, double ang){
        super(x, y, width, height);
        angle = ang;
        Rectangle tst = new Rectangle(); 


    }

    public void move(){
        super.y -= 35;
    }

    public double getAng(){
        return angle;
    }

    public boolean intersects (Rectangle2D r){
        //if intersects
        if (super.intersects(r)){
            return true;
        }
        else{
            return false;
        }

    }


}

I was thinking of maybe turning the the Shape object transformed back into a Polygon to get the point, but I'm not sure how or if that would work.

我想的可能是将Shape对象转换回Polygon以获得重点,但我不确定这是怎么回事。

1 个解决方案

#1

You can use AffineTransform.transform(Point2D, Point2D) to transform a single point on your polygon.

您可以使用AffineTransform.transform(Point2D,Point2D)来变换多边形上的单个点。

Things would be a lot simpler for you if instead of trying to move the ship by using a rotation transform you kept a single (x,y) location of where the ship is. You'd move the ship's location in move() instead of trying to translate the polygon. Then when you want to paint the ship you e.g. do:

如果不是通过使用旋转变换来移动船只,而是保持船舶所在位置的单个(x,y)位置,那么事情会变得更加简单。您将在move()中移动船舶的位置,而不是尝试平移多边形。然后当你想要画船时,例如做:

// Optionally copying the Graphics so the
// transform doesn't affect later painting.
Graphics2D temp = (Graphics2D) g2d.create();
temp.translate(ship.locX, ship.locY);
temp.rotate(ship.angle);
temp.draw(ship);

To move a point based on speed you can do this to find the movement vector:

要根据速度移动点,您可以执行此操作以查找运动矢量:

double velX = speed * Math.cos(angle);
double velY = speed * Math.sin(angle);
locX += timeElapsed * velX;
locY += timeElapsed * velY;

That is essentially a conversion from polar to Cartesian coordinates. The x and y velocities are the legs of a triangle whose hypotenuse is speed and whose known angle is angle:

这实际上是从极坐标到笛卡尔坐标的转换。 x和y速度是三角形的腿,其斜边是速度,其已知角度是角度:

             /|
            / |
           /  |
          /   |
   speed /    |
        /     |
       /      |velY
      / angle |
     /)_______|
         velX

There's an example of doing movement this way in an answer of mine here: https://*.com/a/43692434/2891664.

这里有一个以这种方式进行移动的例子:https://*.com/a/43692434/2891664。

---

For your comments:

对于你的意见:

Are you saying that, unlike my initial move function, just to make ship hold a single point, and thus I would only translate that instead?

你是说这个,不像我最初的移动功能,只是为了让船只保持一个点,因此我只会翻译它?

More or less, yes. You'd still have a polygon to hold the ship's shape, but the points on the polygon would be relative to (0,0).

或多或少,是的。你仍然有一个多边形来保持船的形状,但多边形上的点将相对于(0,0)。

Suppose the following definitions:

假设以下定义:

• Each (x,y) point on the polygon is pi. (In other words, one of p0, p1, p2 and p3.)

多边形上的每个(x,y)点都是pi。 (换句话说,p0,p1,p2和p3之一。)

• The (x,y) coordinates of the translation are T

翻译的(x,y)坐标是T.

Then, after translating the Graphics2D, each pi coordinate becomes pi+T on the panel. So if your polygon points are defined relative to (0,0) then translating to the ship's (locX,locY) will move the polygon to a location relative to (locX,locY).

然后,在翻译Graphics2D之后,每个pi坐标在面板上变为pi + T.因此,如果您的多边形点是相对于(0,0)定义的,则转换为船舶(locX,locY)会将多边形移动到相对于(locX,locY)的位置。

It could be simplest then to define the point which is the tip of the polygon as being (0,0) so that after the translation the tip of the ship is the ship's location:

最简单的是将多边形的尖端定义为(0,0),以便在平移后船的尖端是船的位置:

// Your original points:
int xPoints[] = {800, 780, 800, 820};
int yPoints[] = {400, 460, 440, 460}; 
// Become these points relative to (0,0):
int xPoints[] = {0, -20, 0, 20};
int yPoints[] = {0, 60, 40, 60};

And to e.g. start the ship in the same place, you would initialize its location to (800,400).

并且例如在同一个地方启动船只,你会将其位置初始化为(800,400)。

---

I was thinking about this again and realized the rotation is a little more complicated, because you probably don't want to rotate the ship around the tip. You probably want to rotate the ship around its center.

我再次考虑这一点,并意识到旋转有点复杂,因为你可能不想围绕尖端旋转船。您可能希望围绕其中心旋转船舶。

So, here's an MCVE demonstrating how to do all of this.

所以,这是一个MCVE演示如何做到这一切。

package mcve.game;

import javax.swing.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.Polygon;
import java.awt.RenderingHints;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.Insets;
import java.awt.Toolkit;
import java.awt.GraphicsConfiguration;
import java.util.Set;
import java.util.HashSet;
import java.util.List;
import java.util.ArrayList;

public class MovementExample implements ActionListener {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(MovementExample::new);
    }

    final int fps    = 60;
    final int period = 1000 / fps;

    final JFrame    frame;
    final GamePanel panel;
    final Controls  controls;
    final Ship      ship;

    final List<Bullet> bullets = new ArrayList<>();

    MovementExample() {
        frame = new JFrame("Movement Example");

        Dimension size = getMaximumWindowSize(frame);
        size.width  /= 2;
        size.height /= 2;
        frame.setPreferredSize(size);

        panel = new GamePanel();
        frame.setContentPane(panel);

        frame.pack();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);

        controls = new Controls();

        ship = new Ship(panel.getWidth()  / 2,
                        panel.getHeight() / 2);

        new Timer(period, this).start();
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        double secondsElapsed = 1.0 / fps;
        ship.update(secondsElapsed);

        bullets.forEach(b -> b.update(secondsElapsed));
        Rectangle bounds = panel.getBounds();
        bullets.removeIf(b -> !bounds.contains(b.locX, b.locY));

        panel.repaint();
    }

    class GamePanel extends JPanel {
        GamePanel() {
            setBackground(Color.WHITE);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D) g.create();
            g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                                RenderingHints.VALUE_ANTIALIAS_ON);

            if (ship != null) {
                ship.draw(g2);
            }
            bullets.forEach(b -> b.draw(g2));

            g2.dispose();
        }
    }

    abstract class AbstractGameObject {
        double maxSpeed;
        double rotationAngle;
        double locX;
        double locY;
        double velX;
        double velY;

        AbstractGameObject(double initialX, double initialY) {
            locX = initialX;
            locY = initialY;
        }

        abstract void update(double secondsElapsed);
        abstract void draw(Graphics2D g2);
    }

    class Ship extends AbstractGameObject {
        Polygon shape;
        double  rotationRate;

        Ship(double initialX, double initialY) {
            super(initialX, initialY);
            maxSpeed      = 128; // pixels/second
            rotationAngle = Math.PI * 3 / 2;
            rotationRate  = (2 * Math.PI) / 2; // radians/second

            int xPoints[] = {0, -20, 0, 20};
            int yPoints[] = {0, 60, 40, 60};
            shape = new Polygon(xPoints, yPoints, 4);
        }

        Point2D.Double getTip() {
            Point2D.Double center = getCenter();
            // The tip is at (0,0) and it's already centered
            // on the x-axis origin, so the distance from the
            // tip to the center is just center.y.
            double distance = center.y;
            // Then find the location of the tip, relative
            // to the center.
            double tipX = distance * Math.cos(rotationAngle);
            double tipY = distance * Math.sin(rotationAngle);
            // Now find the actual location of the center.
            center.x += locX;
            center.y += locY;
            // And return the actual location of the tip, relative
            // to the actual location of the center.
            return new Point2D.Double(tipX + center.x, tipY + center.y);
        }

        Point2D.Double getCenter() {
            // Returns the center point of the ship,
            // relative to (0,0).
            Point2D.Double center = new Point2D.Double();
            for (int i = 0; i < shape.npoints; ++i) {
                center.x += shape.xpoints[i];
                center.y += shape.ypoints[i];
            }
            center.x /= shape.npoints;
            center.y /= shape.npoints;
            return center;
        }

        @Override
        void update(double secondsElapsed) {
            // See my answer here: https://*.com/a/43692434/2891664
            // for a discussion of why this logic is the way it is.
            double speed = 0;
            if (controls.isUpHeld()) {
                speed += maxSpeed;
            }
            if (controls.isDownHeld()) {
                speed -= maxSpeed;
            }
            velX  = speed * Math.cos(rotationAngle);
            velY  = speed * Math.sin(rotationAngle);
            locX += secondsElapsed * velX;
            locY += secondsElapsed * velY;

            double rotation = 0;
            if (controls.isLeftHeld()) {
                rotation -= rotationRate;
            }
            if (controls.isRightHeld()) {
                rotation += rotationRate;
            }
            rotationAngle += secondsElapsed * rotation;
            // Cap the angle so it can never e.g. get so
            // large that it loses precision.
            if (rotationAngle > 2 * Math.PI) {
                rotationAngle -= 2 * Math.PI;
            }

            if (controls.isFireHeld()) {
                Point2D.Double tipLoc = getTip();
                Bullet bullet = new Bullet(tipLoc.x, tipLoc.y, rotationAngle);
                bullets.add(bullet);
            }
        }

        @Override
        void draw(Graphics2D g2) {
            Graphics2D copy = (Graphics2D) g2.create();
            copy.setColor(Color.RED);

            // Translate to the ship's location.
            copy.translate(locX, locY);
            // Rotate the ship around its center.
            Point2D.Double center = getCenter();
            // The PI/2 offset is necessary because the
            // polygon points are defined with the ship
            // already vertical, i.e. at an angle of -PI/2.
            copy.rotate(rotationAngle + (Math.PI / 2), center.x, center.y);

            copy.fill(shape);
        }
    }

    class Bullet extends AbstractGameObject {
        Ellipse2D.Double shape = new Ellipse2D.Double();

        Bullet(double initialX, double initialY, double initialRotation) {
            super(initialX, initialY);
            maxSpeed      = 512;
            rotationAngle = initialRotation;
            velX          = maxSpeed * Math.cos(rotationAngle);
            velY          = maxSpeed * Math.sin(rotationAngle);

            double radius = 3;
            shape.setFrame(-radius, -radius, 2 * radius, 2 * radius);
        }

        @Override
        void update(double secondsElapsed) {
            locX += secondsElapsed * velX;
            locY += secondsElapsed * velY;
        }

        @Override
        void draw(Graphics2D g2) {
            Graphics2D copy = (Graphics2D) g2.create();
            copy.setColor(Color.BLACK);
            copy.translate(locX, locY);
            copy.fill(shape);
        }
    }

    // See https://docs.oracle.com/javase/tutorial/uiswing/misc/keybinding.html
    class Controls {
        final Set<Integer> keysHeld = new HashSet<>();

        Controls() {
            bind(KeyEvent.VK_A, "left");
            bind(KeyEvent.VK_D, "right");
            bind(KeyEvent.VK_W, "up");
            bind(KeyEvent.VK_S, "down");
            bind(KeyEvent.VK_SPACE, "fire");
        }

        boolean isLeftHeld()  { return keysHeld.contains(KeyEvent.VK_A); }
        boolean isRightHeld() { return keysHeld.contains(KeyEvent.VK_D); }
        boolean isUpHeld()    { return keysHeld.contains(KeyEvent.VK_W); }
        boolean isDownHeld()  { return keysHeld.contains(KeyEvent.VK_S); }
        boolean isFireHeld()  { return keysHeld.contains(KeyEvent.VK_SPACE); }

        void bind(int keyCode, String name) {
            bind(keyCode, name, true);
            bind(keyCode, name, false);
        }

        void bind(int keyCode, String name, boolean isOnRelease) {
            KeyStroke stroke = KeyStroke.getKeyStroke(keyCode, 0, isOnRelease);
            name += isOnRelease ? ".released" : ".pressed";
            panel.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW)
                 .put(stroke, name);
            panel.getActionMap()
                 .put(name, new AbstractAction() {
                     @Override
                     public void actionPerformed(ActionEvent e) {
                         if (isOnRelease) {
                             keysHeld.remove(keyCode);
                         } else {
                             keysHeld.add(keyCode);
                         }
                     }
                 });
        }
    }

    // This returns the usable size of the display which
    // the JFrame resides in, as described here:
    // http://docs.oracle.com/javase/8/docs/api/java/awt/GraphicsEnvironment.html#getMaximumWindowBounds--
    static Dimension getMaximumWindowSize(JFrame frame) {
        GraphicsConfiguration config = frame.getGraphicsConfiguration();
        Dimension size   = config.getBounds().getSize();
        Insets    insets = Toolkit.getDefaultToolkit().getScreenInsets(config);
        size.width  -= insets.left + insets.right;
        size.height -= insets.top  + insets.bottom;
        return size;
    }
}

There are other ways the tip of the ship could be calculated, but the way I did it in the MCVE is this:

还有其他方法可以计算船的尖端,但我在MCVE中的方式是:

1. Get the center point of the ship, relative to (0,0).

获取船的中心点,相对于(0,0)。

2. Get the distance from the center point to the tip. The tip is at (0,0) so this is just the y-coordinate of the center.

获取从中心点到尖端的距离。尖端位于(0,0),因此这只是中心的y坐标。

3. Then calculate the (x,y) location of the tip, relative to the center. This is done in a very similar way to the figure above for speed and velocity, but the hypotenuse is the distance between the center and the tip of the ship.

然后计算尖端相对于中心的(x,y)位置。这与上图中的速度和速度非常相似,但是斜边是中心和船尖之间的距离。

4. Translate the center to be relative to the ship's location.

将中心翻译为相对于船舶的位置。

5. Translate the location of the tip (which is relative to the center) to be relative to the ship's location.

将尖端的位置(相对于中心)转换为相对于船舶的位置。

It could also all be done with an AffineTransform, similar to what you are doing in the code in the question, but you'd set it on every update. Something like this:

也可以使用AffineTransform完成所有操作,类似于您在问题中的代码中执行的操作,但是您可以在每次更新时设置它。像这样的东西:

AffineTransform transform = new AffineTransform();

@Override
void update(double secondsElapsed) {
    ...
    // Clear the previous translation and rotation.
    transform.setToIdentity();
    // Set to current.
    transform.translate(locX, locY);
    Point2D.Double center = getCenter();
    transform.rotate(rotationAngle + (Math.PI / 2), center.x, center.y);

    if (controls.isFireHeld()) {
        Point2D.Double tip = new Point2D.Double(0, 0);
        transform.transform(tip, tip);
        Bullet bullet = new Bullet(tip.x, tip.y, rotationAngle);
        bullets.add(bullet);
    }
}

You could still use a transform to do calculations that way, but you don't end up with any strangeness from depending on the transform for movement. (In the code in the question, the ship is e.g. only ever moved along the y-axis. The apparent sideways movement is due to the series of rotation concatenations.)

您仍然可以使用变换以这种方式进行计算,但是根据变换的移动,您最终不会有任何异常。 (在问题的代码中,船只例如只沿着y轴移动。明显的侧向移动是由于一系列旋转连接造成的。)