/* pbmlife.c - read a portable bitmap and apply Conway's rules of Life to it
**
** Copyright (C) 1988,1 1991 by Jef Poskanzer.
**
** Permission to use, copy, modify, and distribute this software and its
** documentation for any purpose and without fee is hereby granted, provided
** that the above copyright notice appear in all copies and that both that
** copyright notice and this permission notice appear in supporting
** documentation.  This software is provided "as is" without express or
** implied warranty.
*/

#include "pbm.h"

int
main( argc, argv )
int argc;
char* argv[];
    {
    FILE* ifp;
    bit* prevrow;
    bit* thisrow;
    bit* nextrow;
    bit* temprow;
    register bit* newrow;
    int rows, cols, row;
    register int col, count;
    int format;


    pbm_init( &argc, argv );

    if ( argc > 2 )
        pm_usage( "[pbmfile]" );

    if ( argc == 2 )
        ifp = pm_openr( argv[1] );
    else
        ifp = stdin;

    pbm_readpbminit( ifp, &cols, &rows, &format );
    prevrow = pbm_allocrow( cols );
    thisrow = pbm_allocrow( cols );
    nextrow = pbm_allocrow( cols );

    pbm_writepbminit( stdout, cols, rows, 0 );
    newrow = pbm_allocrow( cols );

    pbm_readpbmrow( ifp, nextrow, cols, format );

    for ( row = 0; row < rows; ++row )
        {
        temprow = prevrow;
        prevrow = thisrow;
        thisrow = nextrow;
        nextrow = temprow;
        if ( row < rows - 1 )
            pbm_readpbmrow( ifp, nextrow, cols, format );

        for ( col = 0; col < cols; ++col )
            {
            /* Check the neighborhood, with an unrolled double loop. */
            count = 0;
            if ( row > 0 )
                {
                /* upper left */
                if ( col > 0 && prevrow[col - 1] == PBM_WHITE )
                    ++count;
                /* upper center */
                if ( prevrow[col] == PBM_WHITE )
                    ++count;
                /* upper right */
                if ( col < cols - 1 && prevrow[col + 1] == PBM_WHITE )
                    ++count;
                }
            /* left */
            if ( col > 0 && thisrow[col - 1] == PBM_WHITE )
                ++count;
            /* right */
            if ( col < cols - 1 && thisrow[col + 1] == PBM_WHITE )
                ++count;
            if ( row < rows - 1 )
                {
                /* lower left */
                if ( col > 0 && nextrow[col - 1] == PBM_WHITE )
                    ++count;
                /* lower center */
                if ( nextrow[col] == PBM_WHITE )
                    ++count;
                /* lower right */
                if ( col < cols - 1 && nextrow[col + 1] == PBM_WHITE )
                    ++count;
                }

            /* And compute the new value. */
            if ( thisrow[col] == PBM_WHITE )
                if ( count == 2 || count == 3 )
                    newrow[col] = PBM_WHITE;
                else
                    newrow[col] = PBM_BLACK;
            else
                if ( count == 3 )
                    newrow[col] = PBM_WHITE;
                else
                    newrow[col] = PBM_BLACK;
            }
        pbm_writepbmrow( stdout, newrow, cols, 0 );
        }

    pm_close( ifp );
    pm_close( stdout );

    exit( 0 );
    }