Java 旋转多边形使其变形

Question

我写了一个方法，它随机生成多边形形状，然后在屏幕上旋转和移动。因为我想检测与这些形状的碰撞，所以我没有使用 Graphics2D 旋转它们，而是使用 AffineTransform 来旋转它们。但出于某种原因，某些形状会因旋转而变得混乱，而其他形状则不受影响。以下是导致问题的形状之一的示例。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Polygon;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.Timer;

public class Test extends JLabel{

    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

    private static final long serialVersionUID = 1L;

    Polygon poly;

    Point center;
    Point source[];
    Point dest[];

    JFrame jf;

    public Test() {

        init();
        createPolygon();

        Timer timer = new Timer(20, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                rotatePoly();
                repaint();
            }});
        timer.start();
    }
    public void rotatePoly() {

        AffineTransform transf = AffineTransform.getRotateInstance(Math.toRadians(2), center.x, center.y);
        transf.transform(source, 0, dest, 0, source.length);

        poly = toPolygon(dest);

    }
    public Polygon toPolygon(Point[] points) {

        Polygon polygon = new Polygon();

        for (int i = 0; i < points.length; i++) {
            polygon.addPoint(points[i].x, points[i].y);
        }
        return polygon;
    }
    public void createPolygon() {

        Point points[] = new Point[7];

        points[0] = new Point(20, 97);
        points[1] = new Point(82, 70);
        points[2] = new Point(134, 70);
        points[3] = new Point(210, 88);
        points[4] = new Point(210, 106);
        points[5] = new Point(144, 125);
        points[6] = new Point(82, 125);

        source = points;
        dest = points;

        poly = toPolygon(points);

        center = new Point(poly.getBounds().x + poly.getBounds().width / 2, poly.getBounds().y + poly.getBounds().height / 2);

    }
    public void init() {

        setVisible(true);
        setSize(260, 260);

        jf = new JFrame();
        jf.setVisible(true);
        jf.setSize(260, 260);
        jf.setContentPane(new JLabel());
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.setLocation((screenSize.width / 2) - (getWidth() / 2), (screenSize.height / 2) - (getHeight() / 2));
        jf.add(this);

    }
    @Override
    public void paintComponent(Graphics g) {

        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(Color.RED);

        g2d.drawPolygon(poly);

    }
}

如果用以下线条替换点，形状基本保持不变。下面的形状当然是对称的，但是旋转方法确实适用于其他随机生成的不均匀形状。

points[0] = new Point(10, 130);
points[1] = new Point(100, 10);
points[2] = new Point(160, 10);
points[3] = new Point(250, 100);
points[4] = new Point(250, 160);
points[5] = new Point(160, 250);
points[6] = new Point(100, 250);

Answer 1

这适用于您的 AffineTransform。它 returns 一个变形的形状而不是修改坐标。我还推荐：

JFrame.setLocationRelativeTo(null); 用于屏幕居中。
使用 RenderingHints 并启用抗锯齿来平滑图形。
由于 Polygon 实现了 Shape，因此需要重新输入一些位置。

class Text extends JLabel{

    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

    private static final long serialVersionUID = 1L;

    Shape poly;

    Point center;
    Point source[];
    Point dest[];

    JFrame jf;

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

        init();
        createPolygon();

        Timer timer = new Timer(20, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                rotatePoly();
                repaint();
            }});
        timer.start();
    }
    public void rotatePoly() {

        AffineTransform transf = 
        AffineTransform.getRotateInstance(Math.toRadians(2), center.x, center.y);
        poly = transf.createTransformedShape(poly);

    }
    public Shape toPolygon(Point[] points) {

        Polygon polygon = new Polygon();

        for (int i = 0; i < points.length; i++) {
            polygon.addPoint(points[i].x, points[i].y);
        }
        return polygon;
    }
    public void createPolygon() {

        Point points[] = new Point[7];

        points[0] = new Point(20, 97);
        points[1] = new Point(82, 70);
        points[2] = new Point(134, 70);
        points[3] = new Point(210, 88);
        points[4] = new Point(210, 106);
        points[5] = new Point(144, 125);
        points[6] = new Point(82, 125);

        source = points;
        dest = points;

        poly = toPolygon(points);

        center = new Point(poly.getBounds().x + poly.getBounds().width / 2, poly.getBounds().y + poly.getBounds().height / 2);

    }
    public void init() {

        setVisible(true);
        setSize(260, 260);

        jf = new JFrame();
        jf.setVisible(true);
        jf.setSize(260, 260);
        jf.setContentPane(new JLabel());
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.setLocation((screenSize.width / 2) - (getWidth() / 2), (screenSize.height / 2) - (getHeight() / 2));
        jf.add(this);

    }
    @Override
    public void paintComponent(Graphics g) {

        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(Color.RED);

        g2d.draw(poly);

    }
}

Answer 2

问题主要是由于多边形使用整数坐标引起的。
不是在多边形本身中累积旋转，而是使用一个变量来保存角度，并在每次更改角度时根据原始多边形计算一个新的多边形。原来的多边形没有改变。

我尽量保持原代码¹:

package cfh.test.sf;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Polygon;
import java.awt.Shape;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.Timer;

public class PolygonTest extends JLabel{

    public static void main(String[] args) {
        new PolygonTest();
    }
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

    private static final long serialVersionUID = 1L;

    Polygon poly;
    Shape rotated;
    Point center;
    int angle = 0;

    JFrame jf;

    public PolygonTest() {

        init();
        createPolygon();

        Timer timer = new Timer(20, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                rotatePoly();
                repaint();
            }});
        timer.start();
    }
    public void rotatePoly() {
        angle += 2;
        AffineTransform transf = AffineTransform.getRotateInstance(Math.toRadians(angle), center.x, center.y);
        rotated = transf.createTransformedShape(poly);
    }
    public Polygon toPolygon(Point[] points) {

        Polygon polygon = new Polygon();

        for (int i = 0; i < points.length; i++) {
            polygon.addPoint(points[i].x, points[i].y);
        }
        return polygon;
    }
    public void createPolygon() {

        Point points[] = new Point[7];

        points[0] = new Point(20, 97);
        points[1] = new Point(82, 70);
        points[2] = new Point(134, 70);
        points[3] = new Point(210, 88);
        points[4] = new Point(210, 106);
        points[5] = new Point(144, 125);
        points[6] = new Point(82, 125);

        poly = toPolygon(points);
        rotated = poly;

        center = new Point(poly.getBounds().x + poly.getBounds().width / 2, poly.getBounds().y + poly.getBounds().height / 2);

    }
    public void init() {

        setVisible(true);
        setSize(260, 260);

        jf = new JFrame();
        jf.setVisible(true);
        jf.setSize(260, 260);
        jf.setContentPane(new JLabel());
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        jf.setLocation((screenSize.width / 2) - (getWidth() / 2), (screenSize.height / 2) - (getHeight() / 2));
        jf.add(this);

    }
    @Override
    public void paintComponent(Graphics g) {

        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(Color.RED);

        g2d.draw(rotated);

    }
}

^{1 - 我宁愿在 paintComponent 内创建旋转形状，而不是在字段中添加其他形状。不确定是否与程序的其余部分冲突（例如计算交集）}

备选方案，未测试：使用 Point2D.Float 或 Point2D.Double 而不是 Point 作为坐标。

Java 旋转多边形使其变形

Java rotating a Polgon deforms it

java

swing

rotation

polygon

affinetransform