仅在一个方向上的鼠标运动侦听器

Question

我一直在研究 Java 中的鼠标运动侦听器，但无法完全解决它，因为我希望对象朝着屏幕上鼠标指向的方向移动，但不幸的是，当鼠标位于小程序窗口内时，对象仅向一个方向移动。下面是我的代码..

import java.awt.*;
import java.awt.geom.*;
import java.util.*;
import java.applet.*;
import java.awt.event.*;
import javax.swing.*;

public class MouseOver extends Applet implements KeyListener, MouseListener,
      MouseMotionListener {
   private int[] Xpoints = { 0, -5, 5 };
   private int[] Ypoints = { -10, -2, -2 };
   private double xpos, ypos;
   private Polygon poly;
   int polyrot = 0;
   private int width; // !! added
   private int height; // !! added

   public void init() {
      poly = new Polygon(Xpoints, Ypoints, Xpoints.length);
      addKeyListener(this);
      addMouseListener(this);
      addMouseMotionListener(this);
   }

   public void paint(Graphics g) {
      Graphics2D g2d = (Graphics2D) g;
      AffineTransform id = new AffineTransform();
      width = getSize().width;
      height = getSize().height;
      g2d.setColor(Color.BLACK);
      g2d.fillRect(0, 0, width, height);
      g2d.setColor(Color.RED);
      g2d.draw(poly);
      g2d.translate(width / 2, height / 2);
      g2d.rotate(Math.toRadians(polyrot));
      g2d.scale(5, 5);
   }

   public void keyReleased(KeyEvent k) {
   }

   public void keyTyped(KeyEvent k) {
   }

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

   public void mouseEntered(MouseEvent m) {
   }

   public void mouseExited(MouseEvent m) {
   }

   public void mouseReleased(MouseEvent m) {
   }

   public void mouseClicked(MouseEvent m) {
   }

   public void mousePressed(MouseEvent m) {
      switch (m.getButton()) {
      case MouseEvent.BUTTON1:
         if (polyrot < 0) {
            polyrot = 359;
            polyrot--;
         }
         repaint();
         break;
      case MouseEvent.BUTTON2:
         if (polyrot > 360) {
            polyrot = 0;
            polyrot++;
         }
         repaint();
         break;
      }
   }

   public void mouseMoved(MouseEvent e) {
      xpos = getX();
      if (xpos < 0) {
         polyrot--;
      } else if (xpos > 0) {
         polyrot++;
      }
      repaint();
      // !! break; // Doesn't belong here
   }

   @Override
   public void mouseDragged(MouseEvent e) {
      // You forgot this method
   }
}

Answer 1

从这里开始：

public void mouseMoved(MouseEvent e){
 xpos=getX();
 if(xpos<0){polyrot--;}
 else if(xpos>0){polyrot++;}
 repaint();
 break;
}

您似乎只更新了 xpos。您还应该更新变量 ypos。 你可能想这样做：

ypos=e.getY();
if (this.ypos<0){
 this.polyrot--;
}else if (this.ypos>0) {
 this.polyrot++;
}
this.repaint();

Answer 2

你的问题在于这一行：

public void mouseMoved(MouseEvent e){
 xpos=getX(); // ******
 if(xpos<0){polyrot--;}
 else if(xpos>0){polyrot++;}
 repaint();
 break;
}

返回小程序的 x 位置而不是鼠标光标。您需要使用 MouseEvent 对象 e 来获取鼠标的位置。将其更改为：

xpos = e.getX();

请不要忽略我对您的问题所做的评论。请记住，我们是帮助我们空闲时间的志愿者。请不要让它变得比帮助你更困难。

---

我已尝试编辑您的代码以使其编译，现在已缩进。考虑创建一个 Swing 应用程序，而不是 AWT 应用程序，因为 Swing 应用程序更加灵活、强大和健壮。

Answer 3

有几件事...

在您的 keyPressed 和 mousePressed 事件中，仅处理越界条件，例如...

if (polyrot < 0) {
    polyrot = 359;
    polyrot++;
}
//...
if (polyrot > 360) {
    polyrot = 0;
    polyrot--;
}

但是当它在可接受的范围内 (0-359) 时，你永远不会处理它应该做什么......

相反，您可以简单地从 polyrot 中添加或减去数量，并允许 API 处理它（令人惊讶的是，它能够处理角度 359），例如...

public void mousePressed(MouseEvent m) {
    switch (m.getButton()) {
        case MouseEvent.BUTTON1:
            polyrot--;
            repaint();
            break;
        case MouseEvent.BUTTON2:
            polyrot++;
            repaint();
            break;
    }
}

现在，我不确定您所说的“对象向屏幕上鼠标指向的方向移动”是什么意思。这是否意味着对象实际上应该改变它的 x/y 坐标，或者它应该只是“看”鼠标光标...

基于您实际上没有移动代码并且基本上将对象绘制在固定位置的事实，我假设“看”...

基本上，你需要知道鼠标在哪里，物体在哪里，然后确定它们之间的角度……

public void mouseMoved(MouseEvent e) {
    int x = width / 2;
    int y = height / 2;

    Point mousePoint = e.getPoint();

    int deltaX = mousePoint.x - x;
    int deltaY = mousePoint.y - y;

    polyrot = -Math.atan2(deltaX, deltaY);
    polyrot = Math.toDegrees(polyrot) + 180;

    repaint();
}

你应该注意到我把 'polyrot' 改成了 'double'

您的paint 方法也是错误的。基本上，您是在转换对象之前绘制对象，相反，您应该使用更像...的东西......

g2d.translate(width / 2, height / 2);
g2d.rotate(Math.toRadians(polyrot));
g2d.draw(poly);

在应用您自己的自定义绘画之前，您还应该致电 super.paint(g)...

附带说明，您应该避免覆盖顶级容器的paint，例如JApplet，而是创建一个自定义组件，从JPanel 之类的东西扩展并覆盖它的paintComponent 方法，执行您的那里的自定义绘画（不要忘记致电super.paintComponent）。更多详情请关注Performing Custom Painting

您还应该避免使用KeyListener，而是使用Key Bindings API，因为它不会遇到KeyListener 会遇到的相同焦点问题...

更新了可运行的示例

所以我尝试了一些代码并制作了这个简单的示例......

基本上，我放弃了Polygon 支持Path2D，主要是因为它提供了更强大的功能并且在扩展时易于处理；）

import java.applet.Applet;
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.Polygon;
import java.awt.Rectangle;
import java.awt.Shape;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.geom.AffineTransform;
import java.awt.geom.Path2D;

public class MouseOver extends Applet implements KeyListener, MouseListener,
                MouseMotionListener {

    private double xpos, ypos;
    private Path2D poly;
    private double polyrot = 0;
    private int width; // !! added
    private int height; // !! added

    public void init() {
        poly = new Path2D.Double();
        poly.moveTo(0, 10);
        poly.lineTo(5, 0);
        poly.lineTo(10, 10);
        poly.lineTo(0, 10);
        poly.closePath();
        addKeyListener(this);
        addMouseListener(this);
        addMouseMotionListener(this);
    }

    public void paint(Graphics g) {
        super.paint(g);;

        Graphics2D g2d = (Graphics2D) g;
        AffineTransform id = new AffineTransform();
        width = getSize().width;
        height = getSize().height;
        g2d.setColor(Color.BLACK);
        g2d.fillRect(0, 0, width, height);
        g2d.setColor(Color.RED);

        id.scale(5, 5);
        Shape scaled = poly.createTransformedShape(id);

        Rectangle bounds = scaled.getBounds();        
        g2d.translate((width - bounds.width) / 2, (height - bounds.height) / 2);
        g2d.rotate(Math.toRadians(polyrot), bounds.width / 2, bounds.height / 2);

        g2d.setStroke(new BasicStroke(5f, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));

        g2d.draw(scaled);
    }

    public void keyReleased(KeyEvent k) {
    }

    public void keyTyped(KeyEvent k) {
    }

    public void keyPressed(KeyEvent k) {
        switch (k.getKeyCode()) {
            case KeyEvent.VK_LEFT:
                polyrot++;
                repaint();
                break;
            case KeyEvent.VK_RIGHT:
                polyrot--;
                repaint();
                break;
        }
    }

    public void mouseEntered(MouseEvent m) {
    }

    public void mouseExited(MouseEvent m) {
    }

    public void mouseReleased(MouseEvent m) {
    }

    public void mouseClicked(MouseEvent m) {
    }

    public void mousePressed(MouseEvent m) {
        switch (m.getButton()) {
            case MouseEvent.BUTTON1:
                polyrot--;
                repaint();
                break;
            case MouseEvent.BUTTON2:
                polyrot++;
                repaint();
                break;
        }
    }

    public void mouseMoved(MouseEvent e) {
        int x = width / 2;
        int y = height / 2;

        Point mousePoint = e.getPoint();

        int deltaX = mousePoint.x - x;
        int deltaY = mousePoint.y - y;

        polyrot = -Math.atan2(deltaX, deltaY);
        polyrot = Math.toDegrees(polyrot) + 180;

        repaint();
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        // You forgot this method
    }
}

Answer 4

这个：

  if (xpos < 0) {

表示“如果光标在面板之外”。

这个：

  xpos = getX();

没有获得鼠标坐标。

把你的活动改成这样：

public void mouseMoved(MouseEvent e) {
    xpos = e.getX();
    if (xpos < getWidth() / 2) {
        polyrot--;
    } else {
        polyrot++;
    }
    repaint();
}

现在如果光标在面板左侧，它会逆时针旋转，如果光标在右侧，它会顺时针旋转。

这个：

  g2d.draw(poly);
  g2d.translate(width / 2, height / 2);
  g2d.rotate(Math.toRadians(polyrot));
  g2d.scale(5, 5);

不会对图像进行任何更改，因为您在绘制后进行变换。

这个：

  Graphics2D g2d = (Graphics2D) g;

这是一个坏主意，因为您正在对全局图形上下文应用变换，这将继续对其他组件进行后续重绘。

把你的颜料改成这样：

public void paint(Graphics g) {
    super.paint(g);
    Graphics2D g2d = (Graphics2D) g.create();
    width = getSize().width;
    height = getSize().height;
    g2d.setColor(Color.BLACK);
    g2d.fillRect(0, 0, width, height);
    g2d.translate(width / 2, height / 2);
    g2d.rotate(Math.toRadians(polyrot));
    g2d.scale(5, 5);
    g2d.setColor(Color.RED);
    g2d.draw(poly);
    g2d.dispose();
}

进一步阅读：

• Painting in AWT and Swing
• How to Write a Mouse Listener