png_adds.hpp

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#ifndef _PNG_ADDS_HPP
#define _PNG_ADDS_HPP

#include <stdio.h>
#include <string>

extern "C" {
        #include "png.h"
}

#include <boost/static_assert.hpp>
#include <boost/gil/gil_config.hpp>
#include <boost/gil/utilities.hpp>
#include <boost/gil/extension/io/io_error.hpp>
#include <boost/gil/extension/io/png_io_private.hpp>

namespace boost {
namespace gil {

namespace detail {

class png_reader_info : public file_mgr
{
protected:
        png_structp _png_ptr;
        png_infop _info_ptr;
        int bit_depth, color_type, interlace_type;

public:
        png_reader_info( const std::string& filename ) : file_mgr( filename.c_str(), "rb" ) { init(); }

        void init()
        {
                char buf[PNG_BYTES_TO_CHECK];

                // read in some of the signature bytes
                io_error_if( fread( buf, 1, PNG_BYTES_TO_CHECK, get() ) != detail::PNG_BYTES_TO_CHECK,
                             "png_check_validity: fail to read file" );
                // compare the first PNG_BYTES_TO_CHECK bytes of the signature.
                io_error_if( png_sig_cmp( (png_bytep)buf, (png_size_t)0, detail::PNG_BYTES_TO_CHECK ) != 0,
                             "png_check_validity: invalid png file" );

                _png_ptr = png_create_read_struct( PNG_LIBPNG_VER_STRING, NULL, NULL, NULL );
                io_error_if( _png_ptr == NULL, "png_get_file_size: fail to call png_create_write_struct()" );
                // allocate/initialize the image information data
                _info_ptr = png_create_info_struct( _png_ptr );
                if( _info_ptr == NULL )
                {
                        png_destroy_read_struct( &_png_ptr, png_infopp_NULL, png_infopp_NULL );
                        io_error( "png_get_file_size: fail to call png_create_info_struct()" );
                }
                if( setjmp( png_jmpbuf( _png_ptr ) ) )
                {
                        //free all of the memory associated with the png_ptr and info_ptr
                        png_destroy_read_struct( &_png_ptr, &_info_ptr, png_infopp_NULL );
                        io_error( "png_get_file_size: fail to call setjmp()" );
                }
                png_init_io( _png_ptr, get() );
                png_set_sig_bytes( _png_ptr, PNG_BYTES_TO_CHECK );
                png_read_info( _png_ptr, _info_ptr );
                if( little_endian() && png_get_bit_depth( _png_ptr, _info_ptr ) > 8 )
                        png_set_swap( _png_ptr );
        }

        virtual ~png_reader_info()
        {
                png_destroy_read_struct( &_png_ptr, &_info_ptr, png_infopp_NULL );
        }

        void read_header()
        {
                png_uint_32 width, height;

                png_get_IHDR( _png_ptr, _info_ptr,
                              &width, &height, &bit_depth, &color_type, &interlace_type,
                              int_p_NULL, int_p_NULL );
        }

        int get_bit_depth()      { return bit_depth; }
        int get_color_type()     { return color_type; }
        int get_interlace_type() { return interlace_type; }
};

}

/// \ingroup PNG_IO
/// \brief Returns the precision of the PNG file at the specified location.
/// Throws std::ios_base::failure if the location does not correspond to a valid PNG file
inline size_t png_read_precision( const std::string& filename )
{
        detail::png_reader_info m( filename );

        m.read_header();
        return m.get_bit_depth();
}


/// \ingroup PNG_IO
/// \brief describes which color/alpha channels are present.
///  PNG_COLOR_TYPE_GRAY        (bit depths 1, 2, 4, 8, 16)
///  PNG_COLOR_TYPE_GRAY_ALPHA  (bit depths 8, 16)
///  PNG_COLOR_TYPE_PALETTE     (bit depths 1, 2, 4, 8)
///  PNG_COLOR_TYPE_RGB         (bit_depths 8, 16)
///  PNG_COLOR_TYPE_RGB_ALPHA   (bit_depths 8, 16)
///  PNG_COLOR_MASK_PALETTE
///  PNG_COLOR_MASK_COLOR
///  PNG_COLOR_MASK_ALPHA
inline size_t png_read_color_type( const std::string& filename )
{
        detail::png_reader_info m( filename );

        m.read_header();
        return m.get_color_type();
}

}
}

#endif  /* _PNG_ADDS_HPP */