围绕一个点旋转一组图形对象？

Question

我在网上找到了一张图片 (http://i.stack.imgur.com/y1oT4.png)，我正在尝试拍摄太阳和天空，让它们围绕屏幕中心旋转，这样太阳和它的光线就好像在旋转。

我打算使用计时器来控制运动，但我不知道如何旋转任意角度。换句话说，我知道如何以 90 为增量旋转（切换宽度和高度），但我想做的是对一组对象进行分组并围绕一个点旋转它们。

我环顾四周，找到了 AffineTransform() 方法，但我不知道这是否真的是我需要的，或者如果需要，如何使用它。

编辑：这能解决我的问题吗？ How to rotate Graphics in Java我会试试更新的。

编辑：它让我更接近，但没有解决它。它返回此运行时错误：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at FallScene.rotateBack(FallScene.java:77)
    at SceneDriver$1TimerListener.actionPerformed(SceneDriver.java:66)
    at javax.swing.Timer.fireActionPerformed(Timer.java:312)
    at javax.swing.Timer$DoPostEvent.run(Timer.java:244)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)
    at java.awt.EventQueue.access$000(EventQueue.java:101)
    at java.awt.EventQueue$3.run(EventQueue.java:666)
    at java.awt.EventQueue$3.run(EventQueue.java:664)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDo
    main.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThre
    ad.java:211)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.
    java:128)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
    ad.java:117)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
    Press any key to continue...

FallScene.rotateBack(FallScene.java:77) 的调用是：

    bg.rotate(Math.toRadians(deg));

...转到：

public void paintComponent(Graphics g) 
{
    super.paintComponent(g);

    // Get the size of the component window
    int w = getWidth();
    int h = getHeight();

    // The Graphics2D object for the BACKGROUND
    Graphics2D bg = (Graphics2D)g;          

    // Sun
    Color solarYellow = new Color(255, 218, 0);
    bg.setPaint(solarYellow);
    Ellipse2D.Double sun = new Ellipse2D.Double((w / 2) - 150, (h / 2) - 150, 300, 300);
    bg.fill(sun); bg.draw(sun);
}

Answer 1

如果你还需要它，我认为这个操作和注释代码应该可以帮助你理解如何绘制它。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;
import java.awt.geom.Path2D;
import java.util.TimerTask;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
import javax.swing.Timer;

public class SunRotate extends JComponent
{  
    public static void main(String[] args) {
        final SunRotate sunRotate = new SunRotate(45);
        JFrame f = new JFrame();
        f.setContentPane(sunRotate);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.pack();
        f.setSize(new Dimension(800, 600));
        f.setVisible(true);
        new java.util.Timer().scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                sunRotate.deltaAngle(.3f);
                sunRotate.repaint();
            }
        }, 16, 16); // every 16 milliseconds
    }


    private float angle;

    public void deltaAngle(float delta) {
        angle += delta;
    }

    public SunRotate(float angle) {
        this.angle = angle;
    }

    public void paintComponent(Graphics g)
    {  
        super.paintComponent(g);

        int w = getWidth();
        int h = getHeight();

        // Recover Graphics2D 
        Graphics2D g2 = (Graphics2D) g;

        // Move and rotate
        g2.translate(w/2.0, h/2.0);
        g2.rotate(Math.toRadians(angle));


        // draw around 0,0
        Color solarYellow = new Color(255, 218, 0);
        g2.setPaint(solarYellow);
        Ellipse2D.Double sun = new Ellipse2D.Double( -150, -150, 300, 300);
        g2.fill(sun);
        { // draw some rays because the sun is round so we don't see the rotation
            // make a ray (triangle)
            Path2D ray = new Path2D.Float();
            ray.moveTo(0, 0);
            ray.lineTo(1000, 50);
            ray.lineTo(1000, -50);
            ray.closePath();
            // draw N rays, rotating each time
            int N = 20;
            for (int i = 0; i < N; i++) {
                g2.fill(ray);
                g2.rotate(Math.PI * 2 / N);
            }
        }
    }

}