Java

Question

我有一个坦克大炮层，它应该向鼠标位置旋转，我用以下代码完成了：

double theta = Math.atan2(point.getY() - center.getY(), point.getX() - center.getX());

然后我相应地旋转图形对象的变换。这可行，但大炮围绕大炮的中心旋转。我希望大炮的底座在旋转发生时保持在原位。我已经尝试了很多不同的位置来旋转，但我找不到一个可以将其底座保持在适当位置的位置。我想我必须将旋转后的图形对象平移到大炮底座应该在的位置，但我不知道该怎么做。我的两层加农炮：

如您所见，底座（浅绿色部分）必须保持在原位。我怎样才能做到这一点？

Answer 1

您的公式只是显示了您如何计算角度 - 您的问题似乎是 'how to rotate an image around a specified point'。为此，我建议使用 AffineTransforms（矩阵数学）。一个很好的起点是：http://docs.oracle.com/javase/tutorial/2d/advanced/transforming.html.

一些示例代码：

Graphics2D g; //<- you should have this in your code somewhere
AffineTransform at = new AffineTransform(); 
at.rotate(theta, centerX, centerY); //<- your question: rotate around specified point
g.setTransform(at); //<- tell the graphics to transform before painting
g.drawImage(...); //<- draws transformed image

如果您深入研究 AffineTransform.rotate(...)，您会发现首先进行平移，然后进行旋转。第三个转换是具有负 x/y 值的翻译。

这是 sun 的旧代码：

public void rotate(double theta, double anchorx, double anchory) {
    // REMIND: Simple for now - optimize later
    translate(anchorx, anchory);
    rotate(theta);
    translate(-anchorx, -anchory);
}

使用矩阵非常强大，因为您可以组合平移、旋转、剪切、镜像等等。不仅在 2d 中，而且在 3d 中。也许你的坦克有一天会离开平坦的世界，成为一个体积模型...

Answer 2

好吧，假设炮塔和基地是分开的图像，并且炮塔和坦克的大小不一样（因为然后它变得复杂......更多然后它实际上是：P）

您可以使用 AffineTransform 并复合转换...

    // This is the x/y position of the top, at the top/left point,
    // I've placed it at the center of my screen, but you get the idea
    double x = (getWidth() - base.getWidth()) / 2d;
    double y = (getHeight() - base.getHeight()) / 2d;

    // Translate the location to the x/y, this makes the top/left 0x0...
    // much easier to deal with...
    AffineTransform at = AffineTransform.getTranslateInstance(x, y);
    g2d.setTransform(at);
    // Draw the base...
    g2d.drawImage(base, 0, 0, this);

    // Offset the turret, in my testing, this was 8x8 from the bases
    // top/left
    at.translate(8, 8);
    if (targetPoint != null) {
        // Calculate the delta between the mouse and the center point
        // of the turret, this is in screen coordinates and not
        // translated coordinates
        double deltaX = (x + 8) - targetPoint.x;
        double deltaY = (y + 8) - targetPoint.y;

        // Calculate the rotation required to point at the mouse
        // Had to apply an offset to allow for the default orientation
        // of the tank...
        double rotation = Math.atan2(deltaY, deltaX) + Math.toRadians(180d);
        // Rotate around the anchor point of the turret
        // Remember, we've translated so the top/left (0x0) is now the
        // turrets default position
        at.rotate(rotation, 4, 4);
    }
    // Transform the Graphics context
    g2d.setTransform(at);
    // Paint the turret
    g2d.drawImage(turret, 0, 0, this);
}
g2d.dispose();

而且因为我努力了...

我的资产...

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.AffineTransform;
import java.awt.geom.Line2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class FollowMe {

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

    public FollowMe() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private Point targetPoint;
        private BufferedImage turret;
        private BufferedImage base;

        public TestPane() {
            addMouseMotionListener(new MouseAdapter() {

                @Override
                public void mouseMoved(MouseEvent e) {
                    targetPoint = e.getPoint();
                    repaint();
                }

            });
            try {
                base = ImageIO.read(getClass().getResource("/Base.png"));
                turret = ImageIO.read(getClass().getResource("/Turret.png"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g.drawLine(getWidth() / 2, 0, getWidth() / 2, getHeight());
            g.drawLine(0, getHeight() / 2, getWidth(), getHeight() / 2);
            if (base != null) {
                double x = (getWidth() - base.getWidth()) / 2d;
                double y = (getHeight() - base.getHeight()) / 2d;
                // Test line from center of tank to mouse poisition
                if (targetPoint != null) {
                    g2d.draw(new Line2D.Double((x + 12), (y + 12), targetPoint.x, targetPoint.y));
                }
                AffineTransform at = AffineTransform.getTranslateInstance(x, y);
                g2d.setTransform(at);
                g2d.drawImage(base, 0, 0, this);
                at.translate(8, 8);
                if (targetPoint != null) {
                    double deltaX = (x + 8) - targetPoint.x;
                    double deltaY = (y + 8) - targetPoint.y;

                    double rotation = Math.atan2(deltaY, deltaX) + Math.toRadians(180d);
                    at.rotate(rotation, 4, 4);
                }
                g2d.setTransform(at);
                g2d.drawImage(turret, 0, 0, this);
            }
            g2d.dispose();
        }

    }

}

查看 Transforming Shapes, Text, and Images 了解更多详情

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