Date: Sun, 2 Feb 1997 00:37:49 -0600 (CST)
From: Andrew Deren <aderen AT eecs DOT uic DOT edu>
To: Pyro Technic <invid AT dmv DOT com>
cc: djgpp AT delorie DOT com
Subject: Re: Bouncing
In-Reply-To: <32F44C1B.2E7B@dmv.com>
Message-ID: <Pine.SUN.3.95.970202003555.13923B-100000@ernie.eecs.uic.edu>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII

I do not know if this is what you want, I just came up with this right
now, it uses some physics to get the velocity, It is used with allegro,
but should not be hard to change to something different, let me know if
this is what you wanted:

#include <allegro.h>
#include <stdio.h>

main()
{
  	allegro_init();  			//initialize allegro
   install_keyboard();  	//install keyboard handler
   install_timer();			//install timer
   set_gfx_mode(GFX_AUTODETECT, 640, 480, 0, 0);	//set graphics
mode to 640x480x256
 	float g= -9.81;	//acceleration of gravity
 	float position;	//current position of the ball
   float time = 0;	//time
   float v_init = 90;	//initial velocity
   char text[80];		//temp string
   BITMAP *ball = create_bitmap(20, 20);	//graphics of the ball
   BITMAP *buffer = create_bitmap(50, 480);	//use double buffer
   clear(ball);
   clear(buffer);
   circle(ball, 10, 10, 9, 15);
   text_mode(0);
	while (1==1) {
     	clear(buffer);
      if (position < 0) {	//make the ball bounce in loops
        	time = 0;
         v_init-=5;	//decrease the initial velocity to accomodate air
resistance
         if (v_init < 0) v_init=0;	//make it stop
      }
   	// formula for position is 1/2 * g * time^2 + v_initial*time
     	position = (0.5)*g*time*time+v_init*time;   //calculate position
      draw_sprite(buffer, ball, 25, 460-(int)position);
      sprintf(text, "%d", (int)position);
      textout(buffer, font, text, 1, 1, 15);	//print current position
      if (key[KEY_ESC]) break;	//make it exit when ESC pressed
	   blit(buffer, screen, 0, 0, 100, 0, 50, 480);
      rest(5);	//rest some time so you can see the ball
      time+=0.1;	//change time
	}
}


On Sun, 2 Feb 1997, Pyro Technic wrote:

> How would I get a ball to bounce realisticly. The constant velocity and
> four directions I have noe just just. Do I need an algorithim,
> logirithm, or some other thing a newbie like myself has never heard of.
> Thanks a lot.
> 
> 	Pyro
>