如何从形状的中心以及屏幕的中心旋转形状

Question

我已经使用drawPolygon()创建了星形，但我想从星形的中心点和屏幕的中心旋转它。

这是我从中心旋转恒星的代码：

@Override
public void paint(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
AffineTransform origX = g2d.getTransform();
AffineTransform newX = (AffineTransform) origX.clone();
newX.rotate(Math.toRadians(angle), x, y + 62);  // Rotate about center of the star
g2d.setTransform(newX);
g2d.drawPolygon(starX, starY, 5);
g2d.dispose();
g.dispose();
}

如果我替换：

newX.rotate(Math.toRadians(angle), x, y + 62);

至

newX.rotate(Math.toRadians(angle), this.getWidth() / 2, this.getHeight() / 2);

我可以从屏幕中央旋转它。

然而，我想同时达到这两种效果。即：就像地球围绕太阳和自己的轴旋转一样。

我尝试创建另一个AffineTransform对象，但当我使用g2d.setTransform(newObj);设置它时，它会覆盖前一个对象

任何建议都将非常有帮助。非常感谢。

如果您想查看，这是我的完整代码

import java.applet.Applet;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.AffineTransform;
public class Star extends Applet implements Runnable{
private int[] starX;
private int[] starY;
private Thread mainThread;
private int x;
private int y;
private int angleFromCenterShape;
@Override
public void init() {
this.setSize(800, 480);
x = 250;
y = 150;
angleFromCenterShape = 0;
starX = new int[5];
starY = new int[5];
mainThread = new Thread(this);
mainThread.start();
this.setBackground(Color.BLACK);
}
@Override
public void paint(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
AffineTransform origX = g2d.getTransform();
AffineTransform newX = (AffineTransform) origX.clone();
newX.rotate(Math.toRadians(angleFromCenterShape), x, y + 65);   //Rotate about center of the star
g2d.setTransform(newX);
g2d.setColor(Color.red);
g2d.fillPolygon(starX, starY, 5);
g2d.dispose();
g.dispose();
}
@Override
public void run() {
while(true){
angleFromCenterScreen = (angleFromCenterScreen + 1) % 360; // angle loop from 0 to 36o
initStar();
try{
Thread.sleep(30);
}catch(Exception e){}
repaint();
}
}
private void initStar(){
starX[0] = x;
starX[1] = x - 50;
starX[2] = x + 75;
starX[3] = x - 75;
starX[4] = x + 50;
starY[0] = y;
starY[1] = y + 130;
starY[2] = y + 50;
starY[3] = y + 50;
starY[4] = y + 130;
}
}

Answer 1

我找到了解决问题的方法，但这不是一个确切的解决方案。然而，在相同的AffineTransform对象上添加另一个rotate()模拟了2次旋转

这是代码

@Override
public void paint(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
AffineTransform origX = g2d.getTransform();
AffineTransform newX = (AffineTransform) origX.clone();
newX.rotate(Math.toRadians(angle), this.getWidth() / 2, this.getHeight() / 2);  // Rotate from the center of screen
newX.rotate(Math.toRadians(angle), x, y + 65);   // Rotate from the center of the shape
g2d.setTransform(newX);
g2d.setColor(Color.red);
g2d.fillPolygon(starX, starY, 5);
g2d.dispose();
g.dispose();
}