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ppm_image.cpp

//FILE:         ppm_image.cpp
//AUTHOR:       Nathan Cournia <nathan@cournia.com>

#include <fstream>
#include "ppm_image.h"

image::image_t*
image::ppm::load( const std::string& filename )
{
        //open file
        std::ifstream stream( filename.c_str( ) );
        if( !stream ) {
                //could not open file
                return NULL;
        }

        //load the file
        image_t* img = load( stream );

        //close the file
        stream.close( );

        //return the image
        return img;
}

image::image_t*
image::ppm::load( std::istream& stream )
{
        //local vars
        char c;

        //first byte must be a 'P'
        stream.read( &c, 1 );
        if( c != 'P' ) return NULL;

        //next byte is a number
        stream.read( &c, 1 );
        if( c == '2' ) {
                return load_ascii_pgm( stream );
        } else if( c == '3' ) {
                return load_ascii_ppm( stream );
        } else if( c == '5' ) {
                return load_binary_pgm( stream );
        } else if( c == '6' ) {
                return load_binary_ppm( stream );
        } else {
                return NULL;
        }
}

bool
image::ppm::can_load( const std::string& filename )
{
        //open file
        std::ifstream stream( filename.c_str( ) );
        if( !stream ) {
                //could not open file
                return false;
        }

        //load the file
        bool loadable = can_load( stream );

        //close the file
        stream.close( );

        //return status
        return loadable;
}

bool
image::ppm::can_load( std::istream& stream )
{
        //local vars
        char c;

        //save current position in stream
        std::streampos save = stream.tellg( );

        //first byte must be a 'P'
        stream.read( &c, 1 );
        if( c != 'P' ) return false;

        //next byte is a number
        stream.read( &c, 1 );

        //return current position to saved value
        stream.seekg( save );
        
        if( (c == '2') || (c == '3') || (c == '5') || (c == '6') ) {
                return true;
        }

        //format unknown
        return false;
}

image::image_t*
image::ppm::load_ascii_pgm( std::istream& stream )
{
        //local vars
        std::string line;
        unsigned int rows, cols, pixels;
        float max, g;
        unsigned int gn;
        
        //get rest of the magic number line
        getline( stream, line );

        //next line can be a comment
        while( stream.peek( ) == '#' ) {
                //this line is a comment
                getline( stream, line );
        }
        
        //read in width
        if( !(stream >> cols) ) return NULL;

        //read in height
        if( !(stream >> rows) ) return NULL;

        //read in max value
        if( !(stream >> max) ) return NULL;
        if( max == 0.0 ) return NULL;

        //create the image
        image_t *img = new image_t( cols, rows, image_t::GREYSCALE, image_t::BYTE );
        img->seek( 0, 0 );

        //read in each pixel
        pixels = rows * cols;
        for( unsigned int i = 0; i < pixels; ++i ) {
                if( !(stream >> g) ) {
                        //either not enough data, or corrupt data
                        delete img;
                        return NULL;
                }

                //normalize and scale colors;
                gn = static_cast<unsigned int>(g / max * 255.0);

                //set pixel
                img->write( gn );
        }

        //all done
        return img;
}

image::image_t*
image::ppm::load_ascii_ppm( std::istream& stream )
{
        //local vars
        std::string line;
        unsigned int rows, cols, pixels;
        float max, r, g, b;
        unsigned int rn, gn, bn;
        
        //get rest of the magic number line
        getline( stream, line );

        //next line can be a comment
        while( stream.peek( ) == '#' ) {
                //this line is a comment
                getline( stream, line );
        }
        
        //read in width
        if( !(stream >> cols) ) return NULL;

        //read in height
        if( !(stream >> rows) ) return NULL;

        //read in max value
        if( !(stream >> max) ) return NULL;
        if( max == 0.0 ) return NULL;

        //create the image
        image_t *img = new image_t( cols, rows, image_t::RGB, image_t::BYTE );
        img->seek( 0, 0 );

        //read in each pixel
        pixels = rows * cols;
        for( unsigned int i = 0; i < pixels; ++i ) {
                if( !(stream >> r >> g >> b) ) {
                        //either not enough data, or corrupt data
                        delete img;
                        return NULL;
                }

                //normalize and scale colors;
                rn = static_cast<unsigned int>(r / max * 255.0);
                gn = static_cast<unsigned int>(g / max * 255.0);
                bn = static_cast<unsigned int>(b / max * 255.0);

                //set pixel
                img->write( rn, gn, bn );
        }

        //all done
        return img;
}

image::image_t*
image::ppm::load_binary_pgm( std::istream& stream )
{
        //local vars
        std::string line;
        unsigned int rows, cols, pixels;
        float max; 
        char g;
        unsigned int gn;
        
        //get rest of the magic number line
        getline( stream, line );

        //next line can be a comment
        while( stream.peek( ) == '#' ) {
                //this line is a comment
                getline( stream, line );
        }
        
        //read in width
        if( !(stream >> cols) ) return NULL;

        //read in height
        if( !(stream >> rows) ) return NULL;

        //read in max value
        if( !(stream >> max) ) return NULL;
        if( max == 0.0 ) return NULL;

        //read in rest of max value line
        getline( stream, line );

        //create the image
        image_t *img = new image_t( cols, rows, image_t::GREYSCALE, image_t::BYTE );
        img->seek( 0, 0 );

        //read in each pixel
        pixels = rows * cols;
        for( unsigned int i = 0; i < pixels; ++i ) {
                if( !stream.read( &g, 1 ) ) {
                        //either not enough data, or corrupt data
                        delete img;
                        return NULL;
                }

                //normalize and scale colors;
                gn = static_cast<unsigned int>(static_cast<unsigned char>( g ) / max * 255.0);

                //set pixel
                img->write( gn );
        }

        //all done
        return img;
}

image::image_t*
image::ppm::load_binary_ppm( std::istream& stream )
{
        //local vars
        std::string line;
        unsigned int rows, cols, pixels;
        float max; 
        char r, g, b;
        unsigned int rn, gn, bn;
        
        //get rest of the magic number line
        getline( stream, line );

        //next line can be a comment
        while( stream.peek( ) == '#' ) {
                //this line is a comment
                getline( stream, line );
        }
        
        //read in width
        if( !(stream >> cols) ) return NULL;

        //read in height
        if( !(stream >> rows) ) return NULL;

        //read in max value
        if( !(stream >> max) ) return NULL;
        if( max == 0.0 ) return NULL;

        //read in rest of max value line
        getline( stream, line );

        //create the image
        image_t *img = new image_t( cols, rows, image_t::RGB, image_t::BYTE );
        img->seek( 0, 0 );

        //read in each pixel
        pixels = rows * cols;
        for( unsigned int i = 0; i < pixels; ++i ) {
                if( !(stream.read( &r, 1 ) &&
                        stream.read( &g, 1 ) &&
                        stream.read( &b, 1 )) ) {
                        //either not enough data, or corrupt data
                        delete img;
                        return NULL;
                }

                //normalize and scale colors;
                rn = static_cast<unsigned int>(static_cast<unsigned char>( r ) / max * 255.0);
                gn = static_cast<unsigned int>(static_cast<unsigned char>( g ) / max * 255.0);
                bn = static_cast<unsigned int>(static_cast<unsigned char>( b ) / max * 255.0);

                //set pixel
                img->write( rn, gn, bn );
        }

        //all done
        return img;
}

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