    // Copyright (C) 2008  Davis E. King (davis@dlib.net), Nils Labugt
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_PNG_LOADER_CPp_
    #define DLIB_PNG_LOADER_CPp_

    // only do anything with this file if DLIB_PNG_SUPPORT is defined
    #ifdef DLIB_PNG_SUPPORT

    #include "../array2d.h"
    #include "../pixel.h"
    #include "../dir_nav.h"
    #include "png_loader.h"
    #include <png.h>
    #include "../string.h"
    #include "../byte_orderer.h"

    namespace dlib
    {

    // ----------------------------------------------------------------------------------------

        struct LibpngData
        {
            png_bytep* row_pointers_;
            png_structp png_ptr_;
            png_infop info_ptr_;
            png_infop end_info_;
        };

    // ----------------------------------------------------------------------------------------

        png_loader::
        png_loader( const char* filename ) : height_( 0 ), width_( 0 )
        {
            read_image( filename );
        }

    // ----------------------------------------------------------------------------------------

        png_loader::
        png_loader( const std::string& filename ) : height_( 0 ), width_( 0 )
        {
            read_image( filename.c_str() );
        }

    // ----------------------------------------------------------------------------------------

        png_loader::
        png_loader( const dlib::file& f ) : height_( 0 ), width_( 0 )
        {
            read_image( f.full_name().c_str() );
        }

    // ----------------------------------------------------------------------------------------

        const unsigned char* png_loader::get_row( unsigned i ) const
        {
            return ld_->row_pointers_[i];
        }

    // ----------------------------------------------------------------------------------------

        png_loader::~png_loader()
        {
            if ( ld_ && ld_->row_pointers_ != NULL )
                png_destroy_read_struct( &( ld_->png_ptr_ ), &( ld_->info_ptr_ ), &( ld_->end_info_ ) );
        }

    // ----------------------------------------------------------------------------------------

        bool png_loader::is_gray() const
        {
            return ( color_type_ == PNG_COLOR_TYPE_GRAY );
        }

    // ----------------------------------------------------------------------------------------

        bool png_loader::is_rgb() const
        {
            return ( color_type_ == PNG_COLOR_TYPE_RGB );
        }

    // ----------------------------------------------------------------------------------------

        bool png_loader::is_rgba() const
        {
            return ( color_type_ == PNG_COLOR_TYPE_RGB_ALPHA );
        }

    // ----------------------------------------------------------------------------------------

        // Don't do anything when libpng calls us to tell us about an error.  Just return to
        // our own code and throw an exception (at the long jump target).
        void png_loader_user_error_fn_silent(png_structp  png_struct, png_const_charp )
        {
            longjmp(png_jmpbuf(png_struct),1);
        }
        void png_loader_user_warning_fn_silent(png_structp , png_const_charp )
        {
        }

        void png_loader::read_image( const char* filename )
        {
            ld_.reset(new LibpngData);
            if ( filename == NULL )
            {
                throw image_load_error("png_loader: invalid filename, it is NULL");
            }
            FILE *fp = fopen( filename, "rb" );
            if ( !fp )
            {
                throw image_load_error(std::string("png_loader: unable to open file ") + filename);
            }
            png_byte sig[8];
            if (fread( sig, 1, 8, fp ) != 8)
            {
                fclose( fp );
                throw image_load_error(std::string("png_loader: error reading file ") + filename);
            }
            if ( png_sig_cmp( sig, 0, 8 ) != 0 )
            {
                fclose( fp );
                throw image_load_error(std::string("png_loader: format error in file ") + filename);
            }
            ld_->png_ptr_ = png_create_read_struct( PNG_LIBPNG_VER_STRING, NULL, &png_loader_user_error_fn_silent, &png_loader_user_warning_fn_silent );
            if ( ld_->png_ptr_ == NULL )
            {
                fclose( fp );
                throw image_load_error(std::string("png_loader: parse error in file ") + filename);
            }
            ld_->info_ptr_ = png_create_info_struct( ld_->png_ptr_ );
            if ( ld_->info_ptr_ == NULL )
            {
                fclose( fp );
                png_destroy_read_struct( &( ld_->png_ptr_ ), ( png_infopp )NULL, ( png_infopp )NULL );
                throw image_load_error(std::string("png_loader: parse error in file ") + filename);
            }
            ld_->end_info_ = png_create_info_struct( ld_->png_ptr_ );
            if ( ld_->end_info_ == NULL )
            {
                fclose( fp );
                png_destroy_read_struct( &( ld_->png_ptr_ ), &( ld_->info_ptr_ ), ( png_infopp )NULL );
                throw image_load_error(std::string("png_loader: parse error in file ") + filename);
            }

            if (setjmp(png_jmpbuf(ld_->png_ptr_)))
            {
                // If we get here, we had a problem writing the file
                fclose(fp);
                png_destroy_read_struct( &( ld_->png_ptr_ ), &( ld_->info_ptr_ ), &( ld_->end_info_ ) );
                throw image_load_error(std::string("png_loader: parse error in file ") + filename);
            }

            png_set_palette_to_rgb(ld_->png_ptr_);

            png_init_io( ld_->png_ptr_, fp );
            png_set_sig_bytes( ld_->png_ptr_, 8 );
            // flags force one byte per channel output
            byte_orderer bo;
            int png_transforms = PNG_TRANSFORM_PACKING;
            if (bo.host_is_little_endian())
                png_transforms |= PNG_TRANSFORM_SWAP_ENDIAN;
            png_read_png( ld_->png_ptr_, ld_->info_ptr_, png_transforms, NULL );
            height_ = png_get_image_height( ld_->png_ptr_, ld_->info_ptr_ );
            width_ = png_get_image_width( ld_->png_ptr_, ld_->info_ptr_ );
            bit_depth_ = png_get_bit_depth( ld_->png_ptr_, ld_->info_ptr_ );
            color_type_ = png_get_color_type( ld_->png_ptr_, ld_-> info_ptr_ );

            if (color_type_ != PNG_COLOR_TYPE_GRAY &&
                color_type_ != PNG_COLOR_TYPE_RGB &&
                color_type_ != PNG_COLOR_TYPE_RGB_ALPHA )
            {
                fclose( fp );
                png_destroy_read_struct( &( ld_->png_ptr_ ), &( ld_->info_ptr_ ), &( ld_->end_info_ ) );
                throw image_load_error(std::string("png_loader: unsupported color type in file ") + filename);
            }

            if (bit_depth_ != 8 && bit_depth_ != 16)
            {
                fclose( fp );
                png_destroy_read_struct( &( ld_->png_ptr_ ), &( ld_->info_ptr_ ), &( ld_->end_info_ ) );
                throw image_load_error("png_loader: unsupported bit depth of " + cast_to_string(bit_depth_) + " in file " + std::string(filename));
            }

            ld_->row_pointers_ = png_get_rows( ld_->png_ptr_, ld_->info_ptr_ );

            fclose( fp );
            if ( ld_->row_pointers_ == NULL )
            {
                png_destroy_read_struct( &( ld_->png_ptr_ ), &( ld_->info_ptr_ ), &( ld_->end_info_ ) );
                throw image_load_error(std::string("png_loader: parse error in file ") + filename);
            }
        }

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_PNG_SUPPORT

    #endif // DLIB_PNG_LOADER_CPp_