From: "23yrold3yrold" <cbarry AT pangea DOT ca>
Newsgroups: comp.os.msdos.djgpp
Subject: Using timers to speed up a program
Date: Sat, 1 Jul 2000 16:24:07 -0500
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To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

Hello. I've been working on a simple vertical scroller engine with DJGPP and
Allegro and had a query. One of the main things tutorials have been
mentioning about creating games is the inclusion of a timer so they will run
the same speed on any computer. Easy enough to slow down a game to run
consistently, but I have a question about speeding them up. A quote from
Allegro's docs:

The standard PC clock only ticks 18.2 times a second, which is not much good
for fast action games. Allegro can replace the system timer routine with a
custom one, which reprograms the clock for higher tick rates while still
calling the BIOS handler at the old speed.

My problem is that when I try to slow the game down, no prob, but it won't
go faster past a certian point. I know graphics ain't quick, but at the
speed this little program runs, it will crawl if I try making something even
half as intense as the first level of any commercial shooter. If anyone can
find a way of increasing the tick rates of the following program, I would
greatly appreciate it. Thank you.


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


volatile int game_time;
void t_handler(void){
     game_time++;
}END_OF_FUNCTION(t_handler);


short int   sx = 0, sy = 0, // for ship's co-ordinates
            key_left = 0,   //  *
            key_right = 0,  //  *  These are for handling
            key_up = 0,     //  *  ship's controls
            key_down = 0;   //  *
PALETTE     pal;
BITMAP     *dbl_buffer;
RLE_SPRITE *ship;

int main()
{

allegro_init();
install_keyboard();
install_timer();

set_color_depth(16);
set_gfx_mode(GFX_AUTODETECT, 640, 480, 0, 0);

LOCK_VARIABLE(game_time);
LOCK_FUNCTION(t_handler);
install_int_ex(t_handler, MSEC_TO_TIMER(5));

ship = get_rle_sprite(load_bmp("Ship.bmp",  pal));

dbl_buffer = create_bitmap(640,480);

do
{
  game_time = 0;

  clear(dbl_buffer);
  draw_rle_sprite(dbl_buffer, ship, sx, sy);
  blit(dbl_buffer, screen, 0, 0, 0, 0, 640, 480);

  key_left  = 0;
  key_right = 0;
  key_up    = 0;
  key_down  = 0;

  do

    if(key[KEY_LEFT]) {key_left  = 1;};
    if(key[KEY_RIGHT]){key_right = 1;};
    if(key[KEY_UP])   {key_up    = 1;};
    if(key[KEY_DOWN]) {key_down  = 1;};
  } while(game_time<10);

  if(key_left ==1)
    {dir = 4; if(sx > 0)   {sx = sx - 5;} else {sx = 0;};};
  if(key_right==1)
    {dir = 6; if(sx < 550) {sx = sx + 5;} else {sx = 550;};};
  if(key_up   ==1)
    {dir = 8; if(sy > 0)   {sy = sy - 5;} else {sy = 0;};};
  if(key_down ==1)
    {dir = 2; if(sy < 365) {sy = sy + 5;} else {sy = 365;};};

} while(!key[KEY_ESC]);

   set_gfx_mode(GFX_TEXT, 0, 0, 0, 0);
   destroy_rle_sprite(ship);
   destroy_bitmap(dbl_buffer);

   return 0;
}