用Graphics2D旋转

Question

我目前正在试验Graphics2D和KeyListener，我目前正在测试旋转物体(在这里是五角大楼)。现在，它工作在旋转的意义上，除了每次按压VK_RIGHT或VK_LEFT时，它应该按1弧度旋转。

但是，目前它只对第一个键按下这样做。从那时起，它创造了一个模式旋转它的1，2，3，4，5.等等，每次弧度(第9键按弧度旋转)，而不是每个按键只有1弧度。

创建JFrame：

import javax.swing.JFrame;


    public class Main {

        public Main() {
            JFrame window = new JFrame("Rotating Hexagons");
            window.setSize(800,600);
            window.setLocationRelativeTo(null);
            window.setResizable(false);
            window.setContentPane(new RotatingHexagon());
            window.pack();
            window.setVisible(true);
        }

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

    }

RotatingHexagon类：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Polygon;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JPanel;


public class RotatingHexagon extends JPanel implements KeyListener {

    private Polygon poly;

    private int[] xpoints = { 0, -10, -7, 7, 10 };
    private int[] ypoints = { -10, -2, 10, 10, -2 };

    private int rotation = 0;

    public RotatingHexagon() {
        setPreferredSize(new Dimension(800,600));
        setFocusable(true);
        requestFocus();
    }

    public void init() {
        poly = new Polygon(xpoints, ypoints, xpoints.length);

        addKeyListener(this);
    }

    public void paint(Graphics g) {
        init();

        Graphics2D g2d = (Graphics2D) g;

        int width = getSize().width;
        int height = getSize().height;

        g2d.setColor(Color.BLACK);
        g2d.fillRect(0, 0, width, height);

        g2d.setColor(Color.WHITE);
        g2d.drawString(rotation + " radians", 10, 20);

        g2d.translate(width / 2, height / 2);
        g2d.scale(20, 20);
        g2d.rotate(Math.toRadians(rotation));

        g2d.setColor(new Color(255, 100, 100));
        g2d.fill(poly);
        g2d.setColor(Color.WHITE);
        g2d.draw(poly);
    }

    public void keyPressed(KeyEvent k) {
        switch(k.getKeyCode()) {
        case KeyEvent.VK_LEFT:
            rotation--;
            if (rotation < 0) rotation = 359;
            repaint();
            break;
        case KeyEvent.VK_RIGHT:
            rotation++;
            if (rotation > 360) rotation = 0;
            repaint();
            break;
        }
    }

    public void keyReleased(KeyEvent k) {}
    public void keyTyped(KeyEvent k) {}

}

我真的不知道为什么它不是每次只旋转1弧度，所以任何帮助都是非常感谢的。谢谢。

Answer 1

原因是一次又一次地调用paint()方法中的init()函数。因此，KeyListener被多次添加，导致它被多次调用，每次按键时都会增加计数器的增量。

将其移动到构造函数：

public RotatingHexagon() {
    setPreferredSize(new Dimension(800,600));
    setFocusable(true);
    requestFocus();
    addKeyListener(this);
}

public void init() {
    poly = new Polygon(xpoints, ypoints, xpoints.length);        
}

安迪

Answer 2

您应该使用持久的AffineTransform来进行旋转。他们要强大得多。

我还在代码中看到了几个问题，您正在每帧调用init方法--这可能是每秒60次。在这个过程中，您将在每个帧中添加一个新的键侦听器。您也正在创建一个新的多边形，这将减慢性能。

我对您的代码做了一些更改，并以AffineTransforms为例。看看这个是否有帮助。

package com.joey.testing;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Polygon;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.geom.AffineTransform;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class AffineTransformTest extends JPanel implements KeyListener {

    private Polygon poly;

    private int[] xpoints = { 0, -10, -7, 7, 10 };
    private int[] ypoints = { -10, -2, 10, 10, -2 };

    private int rotation = 0;
    AffineTransform transform;
    AffineTransform rotationTransform;
    AffineTransform translateTransform;

    public AffineTransformTest() {
        setPreferredSize(new Dimension(800,600));
        setFocusable(true);
        requestFocus();

        //Do Init here - no point in creating new polygon each frame.
        //It also adds the key listener each time
        init();
        updateTransforms();
    }

    public void init() {
        poly = new Polygon(xpoints, ypoints, xpoints.length);
        transform = new AffineTransform();
        rotationTransform = new AffineTransform();
        translateTransform = new AffineTransform();
        addKeyListener(this);
    }

    //Use Paint Compoent
    @Override
    public void paintComponent(Graphics g) {
        //Always call super to clear the screen
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;

        int width = getSize().width;
        int height = getSize().height;

        g2d.setColor(Color.BLACK);
        g2d.fillRect(0, 0, width, height);

        g2d.setColor(Color.WHITE);
        g2d.drawString(rotation + " radians", 10, 20);


        //Store old transform so we can apply it
        AffineTransform old = g2d.getTransform();
        //Add Transform and move polygon
        g2d.setTransform(transform);
        g2d.setColor(new Color(255, 100, 100));
        g2d.fill(poly);
        g2d.setColor(Color.WHITE);
        g2d.draw(poly);
        g2d.setTransform(old);
    }

    public void keyPressed(KeyEvent k) {
        switch(k.getKeyCode()) {
        case KeyEvent.VK_LEFT:
            rotation--;
            if (rotation < 0) rotation = 359;
            repaint();
            break;
        case KeyEvent.VK_RIGHT:
            rotation++;
            if (rotation > 360) rotation = 0;
            repaint();
            break;
        }
        updateTransforms();
    }

    public void updateTransforms(){
        //Resets transform to rotation
        rotationTransform.setToRotation(Math.toRadians(rotation));
        translateTransform.setToTranslation(getWidth()/2, getHeight()/2);

        //Chain the transforms (Note order matters)
        transform.setToIdentity();
        transform.concatenate(translateTransform);
        transform.concatenate(rotationTransform);
    }

    public void keyReleased(KeyEvent k) {}
    public void keyTyped(KeyEvent k) {}


    public static void main(String input[]){
        JFrame f= new JFrame("AffineTransform");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(100, 100);
        f.setResizable(true);
        f.getContentPane().setLayout(new BorderLayout());
        f.getContentPane().add(new AffineTransformTest());
        f.show();

    }
}