#!/usr/local/bin/perl
# Bare CGI program which runs an animation for a set of images with
# a fixed "base" URL.  This achieves true animation, but it is
# very jerky.  
#
# You execute this program as follows: in the ADDRESS field of
# IE 4 you enter this URL:
#
#   staff.washington.edu/larryg/Classes/Rwebl/zz-anim.cgi?f=xxx&d=nnn
#
# where "xxx" is the path name of a file and "nnn" is the delay between
# animations.  For example,
#
# staff.washington.edu/larryg/Classes/Rwebl/zz-anim.cgi?f=../../Image/
# bldg&d=0.2
#
# where"../Image/bldg" is the path name of the set of files (minus
# the "1.gif, 2.gif, etc) and "0.2" is the delay time.
#
# Note: this assumes that there exists a file named "bldg.cnt" in the
# same directory which keeps track of the number of images.
#

             
$request_meth = $ENV{'REQUEST_METHOD'};      
$query_string = $ENV{'QUERY_STRING'};    # get the args delimited by "&"

($imageEQ,$delayEQ) = split(/&/,$query_string);
($dmy,$image_base)  = split(/=/,$imageEQ);      # 1st arg after "?"
($dmy,$delay)       = split(/=/,$delayEQ);      # 2nd arg after "?"


$image_to_read = &increment_image_number( $image_base );

open(FILE, "<" . $image_to_read);
print "Refresh: $delay \n";
print "Content-type: image/gif", "\n\n";
print <FILE>;
close (FILE);
exit(0);


# ^^^^^ gets the next number in the set of images ^^^^^^^^^^^^^^^^^^^^^^^^
sub increment_image_number  
{
  local ($image_base  ) = @_;

  local ($image_count_file);      # File that tracks current GIF image
  local ($image_number);          # Number of the current image
  local ($image_to_read);         # Identifies the actual image

  $image_count_file = $image_base . ".cnt";
 
  if (open(FILE, "<" . $image_count_file)) {
     $image_number = <FILE>;
     close(FILE);
     $image_to_read = $image_base . $image_number . ".gif";
     if (open(FILE2, "<" . $image_to_read)) {
         close (FILE2);
     } else {
        $image_number = 1;
     }
     open(FILE, ">" . $image_count_file);
     print FILE ($image_number+1);
     close(FILE);
     $image_to_read = $image_base . $image_number . ".gif";
     return $image_to_read;
  } else {
     print "Content-type: text/html", "\n\n";
     print "ERROR: cannot find $image_count_file <BR>";
  }
} # vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv