需要绘制投掷球的抛射体运动

Question

所以，我写了一个代码，允许用户以初始角度和速度抛出虚拟对象，以查看它们是否可以接近击球（即基于位置在用户输入上）。

但是，我很难绘制用户输入的角度和虚拟物体速度的曲线。

我已经使用了一个数学公式来计算所述对象的总时间和范围。那就是：

=02sin⁡（一百八十〇分之二） =20sin⁡（/ 180）

我已经尝试过试图把范围和总时间为圆弧状，并绘制它的方式。但这似乎并不奏效。

下面的代码：

import java.awt.AWTEvent; 
import java.awt.*; 
import java.awt.Color; 
import java.awt.Graphics; 
import javax.swing.JFrame; 
import java.util.Scanner; 
import java.awt.geom.QuadCurve2D; 
public class BallGame extends JFrame { 

    public static void main (String[]args) 
    { 
     Scanner cool= new Scanner(System.in); 
     double angle, speed, range, totalTime; 

     { 
      JFrame frame = new JFrame (" Throwing Ball"); 
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
      frame.setSize(700,700); 
     } 

     { 
      System.out.println("Please enter the location of the ball (0 < X < 1)"); 
      StdDraw.setPenRadius(0.06); 
      StdDraw.setPenColor(StdDraw.BLUE); 
      double x, y; 
      y = 0; 
      x = cool.nextDouble(); 
      StdDraw.point(x, y); 
     } 

     System.out.println("Please enter an angle of your choosing:"); 
     angle = cool.nextDouble(); 

     System.out.println("Please enter the speed at wish you which to throw the ball"); 
     speed = cool.nextDouble(); 

     double g; 
     g = 9.8; 
     range = Math.pow(speed, 2) * Math.sin(2 * angle * (Math.PI/180)/g); 
     totalTime = (2 * speed * Math.sin(angle * Math.PI/180))/g; 

Answer 1

用于绘图需要计算水平（x）和垂直（y）的位置，作为时间的函数，开始点，开始速度和角度的曲线。 换句话说，计算水平距离和垂直距离。方程是众所周知的，widely available。

您可以使用这些公式重复计算x，y然后重绘。
请参阅以下演示。没有评论：

import java.awt.BorderLayout; 
import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.RenderingHints; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import java.awt.geom.Point2D; 
import java.util.ArrayList; 
import java.util.List; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.Timer; 

public class BalisticCurve extends JFrame { 

    private static final double G = 9.8; //positive because Y axis is positive going down 
    private int animationSpeed = 5; //millis. The smaller the faster 
    private static int size = 900, ballDiameter = 10; 
    private double startX, startY, ballX, ballY; 
    private double xSpeed, ySpeed, lastPointX, lastPointY; 
    private double time, deltaTime = 0.01 ; //in seconds 
    private List<Point2D> curvePoints= new ArrayList<>(); 
    private Timer timer; 

    BalisticCurve(){ 

     super("Balistic Curve"); 
     DrawBoard board = new DrawBoard(); 
     add(board, BorderLayout.CENTER); 

     ballX= lastPointX = startX = 50; 
     ballY = lastPointY = startY = size - 100; 
     getUserInput(); 

     pack(); 
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     setVisible(true); 

     timer = new Timer(animationSpeed, new ActionListener() { 
      @Override 
      public void actionPerformed(ActionEvent event) { 

       board.moveBall(); 
       board.repaint(); 
       if(! inBounds()) { 
        timer.stop(); 
       } 
      } 
     }); 
     timer.start(); 
    } 

    private void getUserInput() { 

     double angle = 45;//todo replace with user input + verification 
     double speed = 100; 
     xSpeed = speed * Math.cos(angle * (Math.PI/180)); 
     ySpeed = speed * Math.sin(angle * (Math.PI/180)); 
    } 

    private boolean inBounds() { 

     //ignore if ball exceeds height 
     if((ballX < 0) || (ballX > (getWidth())) 
       || (ballY > (getHeight() - ballDiameter))) { 
      return false; 
     } 

     return true; 
    } 

    class DrawBoard extends JPanel { 

     public DrawBoard() { 
      setPreferredSize(new Dimension(size, size)); 
     } 

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

      Graphics2D g2d = (Graphics2D) g; 
      g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
        RenderingHints.VALUE_ANTIALIAS_ON); 
      g2d.setColor(Color.RED); 
      g2d.fillOval((int)ballX,(int)ballY,ballDiameter,ballDiameter); 

      if((Math.abs(lastPointX - ballX)>=1) && (Math.abs(lastPointY - ballY)>=1)) { 
       curvePoints.add(new Point2D.Double(ballX, ballY)); 
       lastPointX = ballX; lastPointY = ballY; 
      } 

      drawCurve(g2d); 
     } 

     private void drawCurve(Graphics2D g2d) { 

      g2d.setColor(Color.BLUE); 
      for(int i=0; i < (curvePoints.size()-1); i++) { 

       Point2D from = curvePoints.get(i); 
       Point2D to = curvePoints.get(i+1); 
       g2d.drawLine((int)from.getX(),(int)from.getY(), (int)to.getX(), (int)to.getY()); 
      } 
     } 

     private void moveBall() { 

      ballX = startX + (xSpeed * time); 
      ballY = startY - ((ySpeed *time)-(0.5 *G * Math.pow(time, 2))) ; 
      time += deltaTime; 
     } 
    } 

    public static void main(String[] args) { 

     new BalisticCurve(); 
    } 
} 

不要犹豫，问什么是不太清楚。