Loading PNG Files

#ifndef LIBPNG_H#define LIBPNG_H#include <boost/shared_ptr.hpp>struct Renderable;boost::shared_ptr< Renderable>  read_png_file( const std::string & file_name );#endif

// g++ main.cpp  libpng.a -lm -lz#include <iostream>#include <cassert>#include <vector>#include <string>#include <stdexcept>//#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <string.h>#include <stdarg.h>#include "libpng.h"		// our interface#include "renderable.h"		#include "timer.h"#define PNG_DEBUG 3#include <png.h>void abort_(const char * s, ...){	va_list args;	va_start(args, s);	vfprintf(stderr, s, args);	fprintf(stderr, "\n");	va_end(args);	abort();}boost::shared_ptr< Renderable>  read_png_file( const std::string &filename)//void read_png_file( const char *filename, Renderable &buffer){	start_timer();	boost::shared_ptr< Renderable>	buffer( new Renderable); 	png_structp		png_ptr;	png_infop		info_ptr;	int number_of_passes;	char header[8];	// 8 is the maximum size that can be checked	/* open file and test for it being a png */	FILE *fp = fopen( filename.c_str(), "rb");	if (!fp) { 		//	abort_("[read_png_file] File %s could not be opened for reading", filename);		throw std::runtime_error( "could not open file");	}		fread(header, 1, 8, fp);	if (png_sig_cmp( (png_byte *)header, 0, 8))		abort_("[read_png_file] File %s is not recognized as a PNG file", filename.c_str());	/* initialize stuff */	png_ptr = png_create_read_struct( PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);		if (!png_ptr)		abort_("[read_png_file] png_create_read_struct failed");	info_ptr = png_create_info_struct(png_ptr);	if (!info_ptr)		abort_("[read_png_file] png_create_info_struct failed");	if (setjmp(png_jmpbuf(png_ptr)))		abort_("[read_png_file] Error during init_io");	// we need gamma handling of color space somewhere 	// ?? 	png_init_io(png_ptr, fp);	png_set_sig_bytes(png_ptr, 8);	png_read_info(png_ptr, info_ptr);	number_of_passes = png_set_interlace_handling(png_ptr);	png_read_update_info(png_ptr, info_ptr);	// bloody hell what a messy interface 	// does it always have an alpha or not an alpha ??	// we want to initialize the io with a pure memory buffer	// the thing is not alpha channedled 	// this is not critical 	assert( sizeof( png_bytep) == 8);	/* read file */	if (setjmp(png_jmpbuf(png_ptr)))		abort_("[read_png_file] Error during read_image");#if 0	// we have the bitdepth ... ie 4 or 8	// but how do we classify -- ugghhh 	std::cout << "------------------------"  << "\n"; 	std::cout << "width/height " << info_ptr->width << ", " << info_ptr->height  << "\n" ; 	std::cout << "color_type   " << (unsigned)info_ptr->color_type << "\n"; 	std::cout << "bit_depth    " << (unsigned)info_ptr->bit_depth << "\n"; 	std::cout << "rowbytes     " << info_ptr->rowbytes  << std::endl;#endif	// what type of structure are we going to use ??	std::vector< png_byte >		buf( info_ptr->height * info_ptr->rowbytes);		std::vector< png_byte*>		rows( info_ptr->height);		for( unsigned y = 0; y < rows.size(); ++y)		rows[ y] = & buf[ y * info_ptr->rowbytes];	png_read_image( png_ptr, &rows[ 0]);    fclose(fp);	buffer->resize( info_ptr->width, info_ptr->height );	for( unsigned y = 0; y < rows.size(); ++y)	{		png_byte *row = rows[ y];		unsigned x = 0;		if( info_ptr->color_type == PNG_COLOR_TYPE_RGB 			&& info_ptr->bit_depth == 8) {  			for( unsigned i = 0; i < info_ptr->width * 3; i += 3)			{				assert( i + 2 < info_ptr->rowbytes);								// potentially need to adjust bitdepth to our 0xff range				unsigned char r = row[ i]; 				unsigned char g = row[ i + 1]; 				unsigned char b = row[ i + 2]; 				unsigned char a = 0xff;				buffer->rbase.copy_pixel( x, y, agg::rgba8( r, g, b, a)); 				++x;			}		}		else if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY			&& info_ptr->bit_depth == 8)		{			for( unsigned i = 0; i < info_ptr->width ; i ++)			{				// potentially need to adjust bitdepth to our 0xff range				unsigned char r = row[ i]; 				unsigned char a = 0xff;				// there's not enough range ?				// r = (r / 2) + 0x7f; 				buffer->rbase.copy_pixel( x, y, agg::rgba8( r, r, r , a)); 				++x;			}		}		else assert( 0);	}//	std::cout << "file '" << filename << "' load time " << elapsed_time() << "ms\n"; 	return buffer;}