import java.applet.Applet;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;

/**
 * Draw a series of images of a "bouncing" ball.  All will appear
 * at once (this is not an animation).  Requires further development
 * by the student.
 * 
 * @author Samuel A. Rebelsky
 * @version 1.0 of August 1999
 */
public class Bounce
  extends Applet
{
  /** Paint the series of images. */
  public void paint(Graphics paintBrush) {
    int repetitions;   // The number of images to show.
    int horiz=0;       // The horizontal position of the center of the ball.
    int vert=0;        // The vertical position of the center of the ball.
    int horizVelocity; // The horizontal velocity of the ball.
    int vertVelocity;  // The vertical velocity of the ball (larger is down).
    int acceleration;  // Downward acceleration due to gravity.
    int elasticity;    // A number between 0 and 100 that represents
                       // how much the ball bounces when it hits the floor.
                       // 0 is "thud".  100 is "superball".
    int left = 0;      // The left edge of the applet's area.
    int top = 0;       // The top edge of the applet's area.
    int right;         // The right edge of the applet's area.
    int bottom;        // The bottom edge of the applet's area.

    // Compute the right and bottom edges.
    Dimension dim = this.getSize();
    right = dim.width;
    bottom = dim.height;

    // Set the background color.
    setBackground(Color.white);

    // Read in the parameters.
    try { repetitions = Integer.parseInt(getParameter("repetitions")); }
    catch (Exception e) { repetitions = 100; }
    try { horizVelocity = Integer.parseInt(getParameter("horizVelocity")); }
    catch (Exception e) { horizVelocity = 10; }
    try { vertVelocity = Integer.parseInt(getParameter("vertVelocity")); }
    catch (Exception e) { vertVelocity = 10; }
    try { acceleration = Integer.parseInt(getParameter("acceleration")); }
    catch (Exception e) { acceleration = 1; }
    try { elasticity = Integer.parseInt(getParameter("elasticity")); }
    catch (Exception e) { elasticity = 100; }

    // And go.  Note that this does not yet make the ball bounce.
    for (int step = 1; step <= repetitions; ++step) {
      // Draw the ball (a filled circle).
      paintBrush.fillOval(horiz-5,vert-5,11,11);

      // Check bouncing at edges
      if ( ((horiz > right-5) && (horizVelocity > 0))
         || ((horiz < 5) && (horizVelocity < 0)) ) {
        horizVelocity = - horizVelocity;
      }
      if ((vert > bottom) && (vertVelocity > 0))
        vertVelocity = - vertVelocity * 9/10;

      // Update the position.
      horiz = horiz + horizVelocity;
      vert = vert + vertVelocity;

      // Update the speed.
      vertVelocity = vertVelocity + acceleration;
    } // for(step)
  } // paint(Graphics)
} // class Bounce