Need to draw projectile motion of a thrown ball

问题

So I'm writing a code that allows a user to throw an imaginary object at an initial angle and speed to see if they can come close to hitting a ball (that is positioned based on user input).

However, I'm having trouble drawing the curve of the users inputted angle and speed of the imaginary object.

I've used a mathematical formula to calculate the total time and range of said object. That is:

𝑟𝑎𝑛𝑔𝑒= 𝑣02sin⁡(2𝜃𝜋/180)𝑔 𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒= 2𝑣0sin⁡(𝜃𝜋/180)𝑔

I've already tried attempting to put range and total time into an arc and plotting it that way. But that didn't seem to work.

Here's the code:

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;

回答1:

For drawing a curve you need to calculate horizontal (x) and vertical (y) position, as a function of time, start point, start speed and angle. In other words, calculate the horizontal distance, and vertical distance. The equations are well known and widely available.

You use these equations to repeatedly calculate x,y and then repaint.
See the following demonstration. Not the comments :

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();
    }
}

Don't hesitate to ask what is not clear enough.

来源：https://stackoverflow.com/questions/47361582/need-to-draw-projectile-motion-of-a-thrown-ball