// Marty Stepp, CSE 142, Autumn 2008
// This program displays the motion of a thrown projectile over time.

import java.awt.*;   // for Graphics

public class Projectile {
	public static final double GRAVITY = -9.81;

	public static void main(String[] args) {
		DrawingPanel panel = new DrawingPanel(400, 300);
		Graphics g = panel.getGraphics();
		
		projectile(g, 60, 50, 10);
		g.setColor(Color.RED);
		projectile(g, 50, 80, 50);
	}
	
	// Plots the motion of a single projectile with the given
	// initial velocity v0, angle, and number of steps to plot.
	public static void projectile(Graphics g, double v0, double angle, int steps) {
		// v0y = v0 sin theta,   v0x = v0 cos theta
		double v0y = v0 * Math.sin(Math.toRadians(angle));
		double v0x = v0 * Math.cos(Math.toRadians(angle));

		// t = -2v0 / a
		double totalTime = -2 * v0y / GRAVITY;
		double dt = totalTime / steps;
		
		System.out.println("       x       y      time");
		for (int i = 0; i <= steps; i++) {
			double t = i * dt;
			double x = v0x * t;
			double y = displacement(v0y, GRAVITY, t);
			System.out.printf("%8.2f %8.2f %8.2f \n", x, y, t);
			g.fillOval( (int) x, (int) (300 - y), 5, 5);
		}
	}
	
	// Computes and returns the change in position of a projectile
	// given its initial velocity v0, acceleration a, and time t.
	public static double displacement(double v0, double a, double t) {
		return (v0 * t + 0.5 * a * Math.pow(t, 2));
	}
}