如何使用Graphics2D实现雪人手臂摆动效果？

我目前正在绘制包含雪人和其他背景元素的图形，绘图部分已完成且效果符合预期，但希望添加动画效果。我使用Graphics2D绘制了所有图形、线条、椭圆等，但不确定能否通过drawLine方法实现雪人手臂的来回摆动。以下是完整的Snowman类代码：

public class Snowman {
    private int x; 
    private int y;
    private int width;
    private int height;
    
public Snowman(int x, int y, int width, int height) {
    this.x=x; 
    this.y=y;
    this.width=width;
    this.height=height;
}
public void draw(Graphics g) 
{
    Graphics2D g2 = (Graphics2D) g;
    
     // the body of the snowman
    g2.setColor(Color.WHITE);
    g2.fillOval(x+125, y+40, 200, 200);
    g2.fillOval(x+75, y+140, 300, 300);
    g2.fillOval(x+25, y+290, 400, 400);

    // the buttons
    g2.setColor(Color.BLACK);
    g2.fillOval(x+210, y+210, 40, 40);
    g2.fillOval(x+210, y+270, 40, 40);
    g2.fillOval(x+210, y+330, 40, 40);

    // the eyes and mouth
    g2.fillOval(x+190, y+98, 20, 20);
    g2.fillOval(x+245, y+98, 20, 20);
    g2.drawArc(x+180, y+120, 100, 50, 200, 140);

    // arm1
    g2.drawLine(x+75, y+270, x, y+90);
   
    //arm2
    g2.drawLine(x+375, y+270, x+450, y+90);
    
    // the hat
    g2.setColor(Color.BLACK);
    g2.fillRect(x+177, y+40, 100, 30);
    g2.fillRect(x+202, y, 50, 50);

  }
}

请问是否有方法实现手臂摆动？还是需要更换绘制方式？

完全可以基于现有的drawLine实现手臂摆动，不需要更换绘制方式，核心思路是用变量控制手臂端点的位置，结合动画循环更新变量值，具体步骤如下：

1. 添加动画控制变量 #

在Snowman类中添加成员变量，用来控制手臂的摆动角度和方向：

// 手臂摆动的角度（弧度）
private double armAngle = Math.toRadians(45);
// 摆动方向，1为正向，-1为反向
private int swingDirection = 1;
// 每次摆动的角度增量（弧度）
private static final double ANGLE_STEP = Math.toRadians(1);
// 摆动的最大/最小角度限制（避免摆幅过大）
private static final double MAX_ANGLE = Math.toRadians(60);
private static final double MIN_ANGLE = Math.toRadians(30);

2. 编写更新手臂角度的方法 #

添加update方法，在每次动画帧刷新时调用，调整手臂的摆动角度：

public void update() {
    armAngle += swingDirection * ANGLE_STEP;
    // 到达角度边界时切换摆动方向
    if (armAngle >= MAX_ANGLE || armAngle <= MIN_ANGLE) {
        swingDirection *= -1;
    }
}

3. 修改draw方法，用角度计算手臂端点坐标 #

原来的手臂端点是固定值，现在通过三角函数计算动态坐标，保证手臂长度不变的同时实现摆动：

// arm1
int arm1StartX = x + 75;
int arm1StartY = y + 270;
// 计算原手臂的长度
int arm1Length = (int) Math.hypot(x - arm1StartX, y + 90 - arm1StartY);
// 根据角度计算新的端点坐标
int arm1EndX = arm1StartX + (int) (arm1Length * Math.cos(Math.PI + armAngle));
int arm1EndY = arm1StartY + (int) (arm1Length * Math.sin(Math.PI + armAngle));
g2.drawLine(arm1StartX, arm1StartY, arm1EndX, arm1EndY);

// arm2
int arm2StartX = x + 375;
int arm2StartY = y + 270;
int arm2Length = (int) Math.hypot(x + 450 - arm2StartX, y + 90 - arm2StartY);
// 用相反角度实现对称摆动
int arm2EndX = arm2StartX + (int) (arm2Length * Math.cos(-armAngle));
int arm2EndY = arm2StartY + (int) (arm2Length * Math.sin(-armAngle));
g2.drawLine(arm2StartX, arm2StartY, arm2EndX, arm2EndY);

4. 在主程序中启动动画循环 #

在窗口或面板类中使用Timer定时调用update和repaint，实现流畅动画：

Timer timer = new Timer(16, e -> {
    snowman.update();
    repaint();
});
timer.start();

16毫秒的间隔对应约60帧/秒的动画帧率。

修改后的完整Snowman类 #

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;

public class Snowman {
    private int x; 
    private int y;
    private int width;
    private int height;
    
    // 手臂摆动控制变量
    private double armAngle = Math.toRadians(45);
    private int swingDirection = 1;
    private static final double ANGLE_STEP = Math.toRadians(1);
    private static final double MAX_ANGLE = Math.toRadians(60);
    private static final double MIN_ANGLE = Math.toRadians(30);
    
    public Snowman(int x, int y, int width, int height) {
        this.x = x; 
        this.y = y;
        this.width = width;
        this.height = height;
    }
    
    public void update() {
        armAngle += swingDirection * ANGLE_STEP;
        if (armAngle >= MAX_ANGLE || armAngle <= MIN_ANGLE) {
            swingDirection *= -1;
        }
    }
    
    public void draw(Graphics g) 
    {
        Graphics2D g2 = (Graphics2D) g;
        
         // the body of the snowman
        g2.setColor(Color.WHITE);
        g2.fillOval(x+125, y+40, 200, 200);
        g2.fillOval(x+75, y+140, 300, 300);
        g2.fillOval(x+25, y+290, 400, 400);

        // the buttons
        g2.setColor(Color.BLACK);
        g2.fillOval(x+210, y+210, 40, 40);
        g2.fillOval(x+210, y+270, 40, 40);
        g2.fillOval(x+210, y+330, 40, 40);

        // the eyes and mouth
        g2.fillOval(x+190, y+98, 20, 20);
        g2.fillOval(x+245, y+98, 20, 20);
        g2.drawArc(x+180, y+120, 100, 50, 200, 140);

        // arm1 - 动态计算端点
        int arm1StartX = x + 75;
        int arm1StartY = y + 270;
        int arm1Length = (int) Math.hypot(x - arm1StartX, y + 90 - arm1StartY);
        int arm1EndX = arm1StartX + (int) (arm1Length * Math.cos(Math.PI + armAngle));
        int arm1EndY = arm1StartY + (int) (arm1Length * Math.sin(Math.PI + armAngle));
        g2.drawLine(arm1StartX, arm1StartY, arm1EndX, arm1EndY);
       
        // arm2 - 动态计算端点
        int arm2StartX = x + 375;
        int arm2StartY = y + 270;
        int arm2Length = (int) Math.hypot(x + 450 - arm2StartX, y + 90 - arm2StartY);
        int arm2EndX = arm2StartX + (int) (arm2Length * Math.cos(-armAngle));
        int arm2EndY = arm2StartY + (int) (arm2Length * Math.sin(-armAngle));
        g2.drawLine(arm2StartX, arm2StartY, arm2EndX, arm2EndY);
        
        // the hat
        g2.setColor(Color.BLACK);
        g2.fillRect(x+177, y+40, 100, 30);
        g2.fillRect(x+202, y, 50, 50);
    }
}

内容的提问来源于stack exchange，提问作者TeeDot