Java GUI旋转和Rectangle的翻译

问题描述

我正在尝试在JPanel中绘制一个矩形，该矩形将平移然后自行旋转以模仿汽车的运动。我已经能够使矩形平移和旋转，但它围绕（0,0）的原点旋转。我非常高兴我可以让矩形移动和旋转，因为我对Java GUI很新，但我似乎无法得到如何让矩形围绕它自己旋转，因为我尝试了更多它，当我初始化矩形并将其旋转45度它的位置已更改，我假设是从旋转方法追加的变换矩阵。

I am trying to draw a rectangle in JPanel that would translate and then rotate itself to mimic the movement of a car. I have been able to make the rectangle translate and rotate, however it rotates around the origin of (0,0). I'm very pleased that I was able to have the rectangle move and rotate as I am very new to Java GUI, but I can not seem to get how to have the rectangle rotate around itself, because I experimented more with it, and when I initialized the rectangle and rotate it 45 degrees it's position was changed, which I would assume is the transform matrix that is appended from the rotate method.

我检查了网站我怎么解决这个问题，但是我只发现了如何旋转矩形，而不是如何像模拟汽车的运动一样旋转和移动。我认为它关注它的变换矩阵，但我只是猜测。所以我的问题是如何让矩形能够旋转并在自身周围移动而不是JPanel中的一个点。

I checked through the site on how would I solve this, however I only found how to rotate a rectangle and not on how to rotate and move like the movement of a simulated car. I would presume it is concerning about its transform matrix, but I'm only speculating. So my question is how would I be able to have the rectangle be able to rotate and move around itself and not against a point in JPanel.

这是我到目前为止的代码：

Here's the code that I have come up so far:

public class Draw extends JPanel implements ActionListener {


private int x = 100;
private int y = 100;
private double theta = Math.PI;

Rectangle rec = new Rectangle(x,y,25,25);

Timer timer = new Timer(25,this);

Draw(){
    setBackground(Color.black);
    timer.start();
}

public void paintComponent(Graphics g){
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D)g;
    g2d.setColor(Color.white);
    rec.x = 100;
    rec.y = 100;
    g2d.rotate(theta);
    g2d.draw(rec);
    g2d.fill(rec);

}

public void actionPerformed(ActionEvent e) {
    x = (int) (x + (Math.cos(theta))*1);
    y = (int) (y + (Math.sin(theta))*1);
    theta = theta - (5*Math.PI/180);
    repaint();
}

推荐答案

通常有两种方法之一使用：

One of two approaches are commonly used:

• 围绕中心旋转图形上下文（ x ， y ） Shape ，如所示。

rotate(double theta, double x, double y)

转换为原点，旋转并转换回来，如。

g2d.translate(this.getWidth() / 2, this.getHeight() / 2);
g2d.rotate(theta);
g2d.translate(-image.getWidth(null) / 2, -image.getHeight(null) / 2);

注意明显的第二个例子中连接的逆序。

Note the apparent reverse order of concatenation in the second example.

附录：仔细观察你的例子，以下更改将旋转 Rectangle 围绕小组的中心。

Addendum: Looking more closely at your example, the following change rotates the Rectangle around the panel's center.

g2d.rotate(theta, getWidth() / 2, getHeight() / 2);

此外，使用 @Override 注释，并给你的小组一个合理的首选大小：

Also, use the @Override annotation, and give your panel a reasonable preferred size:

@Override
public Dimension getPreferredSize() {
    return new Dimension(640, 480);
}

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