// CSE 142, Autumn 2009, Marty Stepp
// This program simulates the dropping of two balls from various heights.
// It draws the balls on a DrawingPanel and animates using the sleep method.
// The purpose of the program is to demonstrate return values
// (the displacement method, and Math methods) and type double.

import java.awt.*;

public class Balls {
    public static void main(String[] args) {
        DrawingPanel panel = new DrawingPanel(600, 600);
        panel.setBackground(Color.CYAN);
        Graphics g = panel.getGraphics();
        
        int ball1x = 100;
        int ball1y = 600 - 600;  // height of 600
        int ball1v0 = 25;
        
        int ball2x = 200;
        int ball2y = 600 - 400;  // height of 400
        int ball2v0 = 0;
        
        // draw the balls at each time increment
        for (double t = 0; t <= 10.0; t = t + 0.1) {
            double disp1 = displacement(ball1v0, 9.81, t);
            g.fillOval(ball1x, ball1y + (int) disp1, 10, 10);

            double disp2 = displacement(ball2v0, 9.81, t);
            g.fillOval(ball2x, ball2y + (int) disp2, 10, 10);

            panel.sleep(50);   // pause for 50 ms
        }
    }
    
    // Computes the displacement of a moving ball
    // with the given initial velocity, acceleration, and time.
    // displacement = v0 t + 1/2 a t^2
    public static double displacement(double v0, double a, double t) {
        double result = v0 * t + 0.5 * a * Math.pow(t, 2);
        return result;
    }
}