java 如何在Java中使用paintComponent来绘制多个东西，但旋转一个？

How to use paintComponent in Java to paint multiple things, but rotate one?

提问by user525479

I'm making a program in Java for my CS class. My teacher has little experience with graphics programing in Java so I've turned to you. I'm currently using the paintComponent method of my main panel to draw two things, one, a rectangle (my cannon, possibly replaced with a image later), and two, a .png file of a cannon ball. I use the Graphics g (which I convert to Graphics2D) to paint the cannon and Ball on to the screen. I then rotate, but, the cannon and ball rotate, not just the cannon. Any tips, suggestions, or helpful tutorials are greatly appreciated.

我正在为我的 CS 课程用 Java 编写程序。我的老师对 Java 图形编程的经验很少，所以我求助于你。我目前正在使用主面板的paintComponent 方法来绘制两个东西，一个是矩形（我的大炮，以后可能会替换为图像），两个是一个炮弹的.png 文件。我使用 Graphics g（我将其转换为 Graphics2D）将大炮和球绘制到屏幕上。然后我旋转，但是，大炮和球旋转，而不仅仅是大炮。非常感谢任何提示、建议或有用的教程。

Here is my code (the commented out links are where I got certain code, ignore them):

这是我的代码（注释掉的链接是我得到某些代码的地方，忽略它们）：

    package Cannon;

import java.awt.geom.Point2D;
import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class NewMain{

public static void main(String[] args) {
FraMainWindow frame = new FraMainWindow();
}
}

class FraMainWindow extends JFrame {
DrawCannon pnlCannon = new DrawCannon();
ButtonPannel pnlButtons = new ButtonPannel();
public FraMainWindow() {
this.setDefaultCloseOperation(JFrame.EXI…
this.setTitle("Super Mario Cannon Bro's");
this.setSize(900, 550);
this.setLayout(new BorderLayout());
this.add(pnlCannon, BorderLayout.CENTER);
this.add(pnlButtons, BorderLayout.SOUTH);
MouseMovement mouseMove = new MouseMovement();
MouseAction mouseClick = new MouseAction();
pnlCannon.addMouseMotionListener(mouseMo…
pnlCannon.addMouseListener(mouseClick);
FireButton actnFire = new FireButton();
pnlButtons.btnFire.addActionListener(act…
this.setVisible(true);
}

public class DrawCannon extends JPanel{
Rectangle.Float rectCannon = new Rectangle.Float(30, 450, 50, 10);
Image imgBall=new ImageIcon("ball.png").getImage();
double dAngle = 0;
boolean isFired = false;
public void addCannonBall(){
isFired=true;
repaint();
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setRenderingHint(RenderingHints.KEY_… RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setRenderingHint(RenderingHints.KEY_… RenderingHints.VALUE_RENDER_QUALITY);//A… Aliasing from http://www.java2s.com/Code/Java/2D-Graph…
g2d.rotate(0 - dAngle, rectCannon.getX(), rectCannon.getY() + 5);
g2d.fill(rectCannon);
if(isFired){
g2d.drawImage(imgBall, 0, 0, null);
}
//Dimension size = getSize();
}
}

public class ButtonPannel extends JPanel {
JButton btnFire = new JButton("Fire!");
ButtonPannel() {
this.add(btnFire);
}
}

public class FireButton implements ActionListener {
public void actionPerformed(ActionEvent e) {
pnlCannon.addCannonBall();
System.out.println("Fire ZE MISSILES");
}
}
public class MouseMovement implements MouseMotionListener {

public void mouseDragged(MouseEvent e) {
double dBase, dHeight, dAngle;
dBase = e.getX() - pnlCannon.rectCannon.getX();
dHeight = pnlCannon.rectCannon.getY() - 5 - e.getY() + 10;
dAngle = Math.atan2(dHeight, dBase);
pnlCannon.dAngle = dAngle;
pnlCannon.repaint();
}//http://download.oracle.com/javase/tutori…

public void mouseMoved(MouseEvent e) {
}
}

public class MouseAction implements MouseListener {

public void mousePressed(MouseEvent e) {
double dBase, dHeight, dAngle;
dBase = e.getX() - pnlCannon.rectCannon.getX();
dHeight = pnlCannon.rectCannon.getY() - 5 - e.getY() + 10;
dAngle = Math.atan2(dHeight, dBase);
pnlCannon.dAngle = dAngle;
pnlCannon.repaint();
}

public void mouseReleased(MouseEvent e) {
}

public void mouseEntered(MouseEvent e) {
}

public void mouseExited(MouseEvent e) {
}

public void mouseClicked(MouseEvent e) {
} // From http://www.rgagnon

采纳答案by Laurence Gonsalves

Try moving this bit:

尝试移动这一点：

if(isFired){
g2d.drawImage(imgBall, 0, 0, null);
}

before this line:

在此行之前：

g2d.rotate(0 - dAngle, rectCannon.getX(), rectCannon.getY() + 5);

Any transformations you apply to your Graphics2Dwill affect anything from that point, so you have to either be careful to apply transforms when you need them, or to "un-apply" them before you don't need them.

您应用到您的任何转换都Graphics2D将从那时起影响任何事情，因此您必须在需要时小心应用转换，或者在不需要它们之前“取消应用”它们。

回答by willcodejavaforfood

You have to unrotate after drawing the cannon and before drawing the ball :)

在绘制大炮之后和绘制球之前，您必须取消旋转:)

You could try to save the transform before you do a rotate and then set it back again. This example is from setTransform in the Java Docs:

您可以尝试在进行旋转之前保存变换，然后再次将其设置回来。此示例来自 Java 文档中的 setTransform：

// Get the current transform
 AffineTransform saveAT = g2.getTransform();
 // Perform transformation
 g2d.transform(...);
 // Render
 g2d.draw(...);
 // Restore original transform
 g2d.setTransform(saveAT);