// CSE 142 Lecture 7
// Math, returns

import java.awt.*; // For Graphics and Color

// This program computes and draws the trajectory of a projectile.
public class Projectile {
	public static final double GRAVITY = -9.81;

	public static void main(String[] args) {
		DrawingPanel panel = new DrawingPanel(420, 250);
		Graphics g = panel.getGraphics();
		
		//            v0, angle, steps
		buildTable(g, 60,    50,    10);
		g.setColor(Color.RED);
		buildTable(g, 50,    80,    50);		
	}
	
	// Calculates the position of an object based on its initial speed, the time
	// elapsed, and the force of acceleration.
	// x = v0 * t + 1/2 * a * t^2
	public static double position(double velocity, double time, double acceleration) {
		return velocity * time + 0.5 * acceleration * Math.pow(time, 2);
	}
	
	// Prints a table of the step, x/y position, and time elapsed for each
	// time step. Also draws the ball's trajectory.
	public static void buildTable(Graphics g, double velocity, double angle, int steps) {
		// Convert angle to radians to find x and y component of velocity.
		double angleRadians = Math.toRadians(angle);
		double vY = velocity * Math.sin(angleRadians);
		double vX = velocity * Math.cos(angleRadians);
		
		double totalTime = -2 * vY / GRAVITY; // The total time the ball spends in the air
		double dT = totalTime / steps; // The time that each step takes
		System.out.printf("%4s%8s%8s%8s\n", "step", "x", "y", "time");
		
		for (int i = 0; i <= steps; i++) {
			double elapsed = dT * i;
			double x = position(vX, elapsed, 0);
			double y = position(vY, elapsed, GRAVITY);
			System.out.printf("%4d%8.2f%8.2f%8.2f\n", i, x, y, elapsed);
			g.fillOval((int)x, 250 - (int)y, 5, 5);
		}
	}
}