​我的要求是每点击一次按钮，逆时针旋转固定角度90度，求！

Question

我想请教各位Graphics2D中的
g2d.rotate(Math.PI/2, 200, 200);
是不是指将图片以（200， 200）为旋转中心，逆时针旋转90度？

另外我写了个很小的测试程序，但是点击旋转按钮，图片怎么都不旋转，请教高手是什么问题，代码如下：
//MyPanel.java

import java.awt.*;

import javax.swing.*;

public class MyPanel extends JPanel{

private Graphics g;
private Image image;

public void paintComponent(Graphics g){
this.g = g;
image = new ImageIcon("src/test.jpg").getImage();
g.drawImage(image, 3, 4, this);
}

public Graphics getGraphic(){
return g;
}

public Image getImage(){
return image;
}

}

//DrawImage.java
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

public class DrawImage implements ActionListener {

JFrame frame; //主窗体
MyPanel panel;
JButton rotate; //控制旋转的按钮

public DrawImage(){
frame = new JFrame("绘图Demo");
frame.setSize(400, 500);
frame.setAlwaysOnTop(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(null);
frame.setVisible(true);

panel = new MyPanel();
panel.setBounds(0, 0, 400, 400);
frame.getContentPane().add(panel);

rotate = new JButton("逆旋"); //每按一次逆时针旋转90度
rotate.setBounds(5, 405, 390, 90);
frame.getContentPane().add(rotate);
rotate.addActionListener(this);

}

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

public void actionPerformed(ActionEvent e) {
Graphics g = panel.getGraphic();
Graphics2D g2d = (Graphics2D)g;
g2d.rotate(Math.PI/2, 200, 200);
g2d.drawImage(panel.getImage(), 0, 0, 400, 400, null);
}

}
不胜感激！

Answer 1

代码有问题。帮你改好了，你试试import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.Image;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.ImageIcon;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JPanel;class MyPanel extends JPanel {private int xuanzhuan = 0;private Image image;public void paintComponent(Graphics g) {Graphics2D g2d = (Graphics2D) g;g2d.fillRect(0, 0, 400, 400);g2d.rotate(xuanzhuan, 200, 200);image = new ImageIcon("src/test.jpg").getImage();g2d.drawImage(image, 0, 0, this);g.dispose();}public Image getImage() {return image;}public int getXuanzhuan() {return xuanzhuan;}public void setXuanzhuan(int xuanzhuan) {this.xuanzhuan = xuanzhuan;}}public class DrawImage implements ActionListener {JFrame frame; // 主窗体MyPanel panel;JButton rotate; // 控制旋转的按钮public DrawImage() {frame = new JFrame("绘图Demo");frame.setSize(400, 500);frame.setAlwaysOnTop(true);frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frame.setLayout(null);frame.setVisible(true);panel = new MyPanel();panel.setBounds(0, 0, 400, 400);frame.getContentPane().add(panel);rotate = new JButton("逆旋"); // 每按一次逆时针旋转90度rotate.setBounds(5, 405, 390, 90);frame.getContentPane().add(rotate);rotate.addActionListener(this);}public static void main(String[] args) {new DrawImage();}public void actionPerformed(ActionEvent e) {panel.setXuanzhuan(panel.getXuanzhuan() + 1);panel.repaint();}}

Answer 2

ctx = document.getElementByIdx_x_x_x('canvas').getContext('2d');ctx.fillStyle = "rgb(250,0,0)";ctx.save();ctx.translate(50,50); //这个translate(50，50)发生在rotate()之前,其目的是将旋转点从默认点(0，0),移动到(50，50),下面紧跟着的rotate就是按照这个点来转//rotate方法的旋转点完全是按照[在其上\紧跟着它的]translate来确定旋转点的.ctx.rotate(-Math.PI/8);ctx.translate(-50,-50);//这个translate是在rotate之下,也就是rotate已经转过了再执行translate(-50,-50),它其实也是将坐标点从(50，50)重新移到了(0，0),紧跟在他下面的rotate旋转中心就是按照(0，0)来旋转的ctx.fillRect(50,50,100,200);//ctx.beginPath();ctx.fillStyle="rgb(0,255,0)"ctx.rotate(-Math.PI/6);ctx.fillRect(50,50,100,200);ctx.restore();ctx.fillStyle = "rgb(0,0,250)";ctx.fillRect(50,50,5,5);总结:这里的translate就是移动中心点的.旋转中心默认是在canvas的左上角.

Answer 3

在事件中加入repaint();