Message-ID:	<366AB03F.DC924D2@geocities.com>
From:	Sahab Yazdani <sahaby AT geocities DOT com>
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Newsgroups:	comp.os.msdos.djgpp
Subject:	Compression Algo... (Please Help)
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Date:	Sun, 06 Dec 1998 16:26:39 +0000
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

I've created a simple run-length compression Algorytm for graphics for a
project...  The project was to convert the PCX (256 colour) format into
my own format, anyways I realized that converting to a raw format was
going to make the files too big.  So I decided on the run-length.  My
code was designed like this:  Covert the PCX file to a raw graphic (no
compression) and then take that data and compress.  

(The portion of my code that reads the original PCX file is ok and works
fine)

My compression code will leave out the Header that includes the size of
the image and the palette information (This is (256 * 3) + 4 bytes long)
and just write them into the output file.  And then reads 3 bytes from
the file, sees if they are the same (a=b=c)

Now if they are the same, it keeps on reading until a byte that doesn't
equal a. It counts how many of the same it took (up to 256) and writes
two bytes into the output file (the colour of the pixel, and then the
number of occurances).  now if they weren't the same it'll still write
two bytes to the output file:  the colour of the pixel and 0 to indicate
that the pixel only happend once. Then repeats...

This is generally it, so heres the code (doesn't include conversion of
PCX to raw...):

ART2CMP.CC

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

// Simple Run-Length Compressor

int main( int argc, char *argv[] ) {
     FILE *in, *out;
     long counter;
     unsigned char run_length[3];
     unsigned char next;
     long run_counter = 0;
     int first = 1;

     if ( argc != 3 ) {
        printf( "Usage: ART2CMP.EXE [source] [destination]\n" );
        return 1;
     }

     in = fopen( argv[1], "rb" );
     out = fopen( argv[2], "wb" );
     if ( in == NULL ) {
        printf( "Input file is not found or corrupted\n" );
        return 1;
     }
     if ( out == NULL ) {
        printf( "Output file is not found or corrupted\n" );
        fclose( in );
        return 1;
     }

     printf( "Compressing..." );
     fflush( stdout );

     for ( counter=0;counter<(255 * 3) + 4 ;counter++ ) {
         fputc( fgetc( in ), out );
     }

     while ( !feof( in ) ) {
           run_length[0] = fgetc( in );
           run_length[1] = fgetc( in );
           run_length[2] = fgetc( in );

           if ( ( run_length[0] == run_length[1] ) && ( run_length[0] ==
run_length[2] ) ) {
              while ( run_counter != 255 ) {
                    next = fgetc( in );
                    if ( next != run_length[0] )
                       break;
                    run_counter++;
              }
              fputc( run_length[0], out );
              fputc( run_counter, out ); // Number of occurances + 3

              printf( "%i, %i\n", run_length[0], run_counter );

              first = 1;
              run_counter = 0;
           } else {
             fseek( in, -2, SEEK_CUR ); // Move back 2 spaces
             fputc( run_length[0], out );
             fputc( 0, out ); // Only 1 occurance

             printf( "%i, %i\n", run_length[0], 0 ); // I port to a file
to make sure that the output is correct
//             run_length[0] = run_length[1];
//             run_length[1] = run_length[2];
           }
     }
     printf( "Done!\n" );

     fclose( in );
     fclose( out );

     return 1;
}

Now i'm not sure but I think that this is also working fine but that my
decoder is kinda screwed...

DECODER.CC - Method LoadFile()

int LoadFile() {
   FILE *in;
   unsigned int counter=0;
   unsigned char run_length[2];
   unsigned int count;

   in=fopen( filename, "rb" );

   if (in==NULL) {
   	return 0;
   }

   length = ( fgetc(in) * 256 ) + fgetc(in);
   width = ( fgetc(in) * 256 ) + fgetc(in);

   bmp_ptr = (unsigned char *) malloc( GetLength() * GetWidth() );
   if (bmp_ptr==NULL) {
   	return 0;
   }

   for (counter=0;counter<255;counter++) {
   	palette->SetRGB( counter, GRGB( fgetc( in ), fgetc( in ), fgetc( in
) ) );
	}

/*   for (counter=0;counter<GetLength() * GetWidth();counter++) {
   	bmp_ptr[counter]=fgetc(in);
   } */ // Originally intended for a non-compressed test
   fseek( in, (256 * 3) + 3, SEEK_SET );

   while ( counter < GetLength() * GetWidth() ) {
      run_length[0] = fgetc( in );
      run_length[1] = fgetc( in );

      if ( run_length[1]!=0 ) {
//      	counter++;
      	while (count<run_length[1] + 6) {
            counter++;
         	bmp_ptr[counter] = run_length[0];
            count++;
         }
//         counter+=count;
         count=0;
      } else {
         counter++;
      	bmp_ptr[counter] = run_length[0];
      }
   }

   fclose(in);

   return 1;
}

All my other functions work ok, cause i've tested them without the
compression algo.

The output is *really* off being just a bunch of dots...

I've compared outputs of the two files that say that the reading of the
file is correct.

Please see if you can help...
-- 
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* Sahab Yazdani              *    Let the Dragon ride again on the   *
* Thornhill Secondary School *     winds of Time - Wheel of Time     *
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