/*******************************************************************************
 * png.cpp
 *
 * This module contains the code to read and write the PNG output file
 *
 * ---------------------------------------------------------------------------
 * Persistence of Vision Ray Tracer ('POV-Ray') version 3.7.
 * Copyright 1991-2013 Persistence of Vision Raytracer Pty. Ltd.
 *
 * POV-Ray is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * POV-Ray is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 * ---------------------------------------------------------------------------
 * POV-Ray is based on the popular DKB raytracer version 2.12.
 * DKBTrace was originally written by David K. Buck.
 * DKBTrace Ver 2.0-2.12 were written by David K. Buck & Aaron A. Collins.
 * ---------------------------------------------------------------------------
 * $File: //depot/public/povray/3.x/source/base/image/png.cpp $
 * $Revision: #1 $
 * $Change: 6069 $
 * $DateTime: 2013/11/06 11:59:40 $
 * $Author: chrisc $
 *******************************************************************************/

/*****************************************************************************
*  This code requires the use of libpng, Group 42's PNG reference library.
*  libpng is  Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
*
*  This code also requires the use of Zlib,
*  Zlib is Copyright (C) 1995 Jean-loup Gailly and Mark Adler
*
*  The latest version of these libraries are available at ftp.uu.net as
*
*  /graphics/png/libpngXX.tar.gz.
*  /archiver/zlib/zlib-XX.tar.gz.
*
*  where XX is the latest version of the library.
*
*****************************************************************************/

// NOTE: this file throws exceptions from 'extern C' functions. be sure to enable
// this in your compiler options (preferably for this file only).

#include <boost/scoped_ptr.hpp>
#include <boost/scoped_array.hpp>

#include <string>

// configbase.h must always be the first POV file included within base *.cpp files
#include "base/configbase.h"
#include "base/image/image.h"
#include "base/fileinputoutput.h"
#include "base/image/png_pov.h"
#include "base/types.h"
#include "base/povmsgid.h" // for kPOVList_GammaType_SRGB

#ifndef LIBPNG_MISSING

#include <png.h>
#include "metadata.h"

// this must be the last file included
#include "base/povdebug.h"


namespace pov_base
{

namespace Png
{

/*****************************************************************************
* Local preprocessor defines
******************************************************************************/

/* Number of scanlines between output flushes, and hence the maximum number of
 * lines lost for an interrupted render.  Note that making it much smaller
 * than about 10 for a 640x480 image will noticably degrade compression.
 * If a very small buffer is specified, we don't want to flush more than once
 * every 10 lines or so (assuming a 2:1 compression ratio).
 */
const int FLUSH_DIST = 16; // Set to 16 and removed complicated math [trf]
const int NTEXT = 15;      // Maximum number of tEXt comment blocks
const int MAXTEXT = 1024;  // Maximum length of a tEXt message


/*****************************************************************************
* Local typedefs
******************************************************************************/
struct Messages
{
	vector<string> warnings;
	string error;
};

/*****************************************************************************
* Local variables
******************************************************************************/

/*****************************************************************************
* Static functions
******************************************************************************/


extern "C"
{
	// These are replacement error and warning functions for the libpng code
	void png_pov_err(png_structp, png_const_charp);
	void png_pov_warn(png_structp, png_const_charp);
	void png_pov_read_data(png_structp, png_bytep, png_size_t);
	void png_pov_write_data(png_structp, png_bytep, png_size_t);
	void png_pov_flush_data(png_structp);


	/*****************************************************************************
	*
	* FUNCTION      : png_pov_warn
	*
	* ARGUMENTS     : png_struct *png_ptr; char *msg;
	*
	* MODIFIED ARGS :
	*
	* RETURN VALUE  :
	*
	* AUTHOR        : Andreas Dilger
	*
	* DESCRIPTION
	*
	*   Prints an warning message using the POV I/O functions.  This uses the
	*   png io_ptr to determine whether error messages should be printed or
	*   not.
	*
	* CHANGES
	*
	******************************************************************************/

	void png_pov_warn(png_structp png_ptr, png_const_charp msg)
	{
		Messages *m = (Messages *)png_get_error_ptr(png_ptr);

		if (m)
			m->warnings.push_back (string(msg)) ;
	}


	/*****************************************************************************
	*
	* FUNCTION      : png_pov_err
	*
	* ARGUMENTS     : png_struct *png_ptr; char *msg;
	*
	* MODIFIED ARGS :
	*
	* RETURN VALUE  :
	*
	* AUTHOR        : Andreas Dilger
	*
	* DESCRIPTION
	*
	*   If the png io_ptr is true, this prints an error message using the POV
	*   I/O function, then throws an exception.
	*
	* CHANGES
	*
	******************************************************************************/

	void png_pov_err(png_structp png_ptr, png_const_charp msg)
	{
		Messages *m = (Messages *)png_get_error_ptr(png_ptr);

		if (m)
			m->error = string(msg) ;
		throw POV_EXCEPTION(kFileDataErr, msg);
	}


	/*****************************************************************************
	*
	* FUNCTION      : png_pov_read_data
	*
	* ARGUMENTS     : png_structp png_ptr; png_bytep data; png_uint_32 length;
	*
	* MODIFIED ARGS :
	*
	* RETURN VALUE  :
	*
	* AUTHOR        : Thorsten Froehlich
	*
	* DESCRIPTION
	*
	*   Replacement read function.
	*
	* CHANGES
	*
	******************************************************************************/

	void png_pov_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
	{
		IStream *file = (IStream *)png_get_io_ptr(png_ptr);

		if (!file->read ((char *)data, length))
		{
			Messages *m = (Messages *)png_get_error_ptr(png_ptr);
			if (m)
				m->error = string("Cannot read PNG data");
			throw POV_EXCEPTION(kFileDataErr, "Cannot read PNG data");
		}
	}


	/*****************************************************************************
	*
	* FUNCTION      : png_pov_write_data
	*
	* ARGUMENTS     : png_structp png_ptr; png_bytep data; png_uint_32 length;
	*
	* MODIFIED ARGS :
	*
	* RETURN VALUE  :
	*
	* AUTHOR        : Thorsten Froehlich
	*
	* DESCRIPTION
	*
	*   Replacement write function.
	*
	* CHANGES
	*
	******************************************************************************/

	void png_pov_write_data(png_structp png_ptr, png_bytep data, png_size_t length)
	{
		OStream *file = (OStream *)png_get_io_ptr(png_ptr);

		if (!file->write ((char *)data, length))
		{
			Messages *m = (Messages *)png_get_error_ptr(png_ptr);
			if (m)
				m->error = string("Cannot write PNG data");
			throw POV_EXCEPTION(kFileDataErr, "Cannot write PNG data");
		}
	}


	/*****************************************************************************
	*
	* FUNCTION      : png_pov_flush_data
	*
	* ARGUMENTS     : png_structp png_ptr;
	*
	* MODIFIED ARGS :
	*
	* RETURN VALUE  :
	*
	* AUTHOR        : Thorsten Froehlich
	*
	* DESCRIPTION
	*
	*   Replacement flush function.
	*
	* CHANGES
	*
	******************************************************************************/

	void png_pov_flush_data(png_structp png_ptr)
	{
		OStream *file = (OStream *)png_get_io_ptr(png_ptr);
		file->flush();
	}

	static bool ReadPNGUpdateInfo (png_structp png_ptr, png_infop info_ptr)
	{
		if (setjmp(png_jmpbuf(png_ptr)))
		{
			// If we get here, we had a problem reading the file
			return (false) ;
		}
		png_read_update_info(png_ptr, info_ptr);
		return (true);
	}

	static bool ReadPNGImage (png_structp r_png_ptr, png_bytepp row_ptrs)
	{
		if (setjmp(png_jmpbuf(r_png_ptr)))
		{
			// If we get here, we had a problem reading the file
			return (false) ;
		}
		png_read_image(r_png_ptr, row_ptrs);
		return (true);
	}
}

/*****************************************************************************
*
* FUNCTION      : Read_Png_Image
*
* ARGUMENTS     : IMAGE *Image; char *name;
*
* MODIFIED ARGS : Image
*
* RETURN VALUE  : none
*
* AUTHOR        : Andreas Dilger
*
* DESCRIPTION
*
*   Reads a PNG image into an RGB image buffer
*
* CHANGES
*
*   Updated for POV-Ray 3.X - [TIW]
*   Updated to allow grayscale and alpha together, Oct 1995 - [AED]
*   Fixed palette size for grayscale images with bit-depth <= 8, Nov 1995 [AED]
*   Changed how grayscale images > 8bpp are stored based on use, Nov 1995 [AED]
*
******************************************************************************/

// TODO: use scoped clean-up class in case of exception
Image *Read (IStream *file, const Image::ReadOptions& options)
{
	int                   stride;
	int                   j;
	png_info              *r_info_ptr;
	png_byte              **row_ptrs;
	png_struct            *r_png_ptr;
	unsigned int          width;
	unsigned int          height;
	Messages              messages;
	Image                 *image = NULL;

	if ((r_png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, (png_voidp)(&messages), png_pov_err, png_pov_warn)) == NULL)
		throw POV_EXCEPTION(kOutOfMemoryErr, "Cannot allocate PNG data structures");
	if ((r_info_ptr = png_create_info_struct(r_png_ptr)) == NULL)
		throw POV_EXCEPTION(kOutOfMemoryErr, "Cannot allocate PNG data structures");

	// set up the input control
	png_set_read_fn(r_png_ptr, file, png_pov_read_data);

	// read the file information
	png_read_info(r_png_ptr, r_info_ptr);

	// PNG files are pretty clear about Gamma:
	// - If an ICC profile is present, that information should be used (but currently we don't, because that would be a lot of work).
	// - Otherwise, if an sRGB chunk is present, the image uses sRGB color space.
	// - Otherwise, if a gAMA chunk is present, the image uses the specified power-law gamma encoding.
	// - Otherwise, PNG/W3C recommendation is to assume that the image uses sRGB color space nonetheless.
	GammaCurvePtr gamma;
	if (options.gammacorrect)
	{
		if (options.gammaOverride) // user wants to override information, let them have their will
			gamma = TranscodingGammaCurve::Get(options.workingGamma, options.defaultGamma);
#if defined(PNG_sRGB_SUPPORTED) && defined(PNG_READ_sRGB_SUPPORTED)
		else if (png_get_valid(r_png_ptr, r_info_ptr, PNG_INFO_sRGB)) // file has a sRGB chunk, indicating sRGB color space
		{
			gamma = TranscodingGammaCurve::Get(options.workingGamma, SRGBGammaCurve::Get());
		}
#endif
#if defined(PNG_gAMA_SUPPORTED) && defined(PNG_READ_gAMA_SUPPORTED)
		else if (png_get_valid(r_png_ptr, r_info_ptr, PNG_INFO_gAMA)) // file has a gAMA chunk, indicating the encoding gamma
		{
			double file_gamma = 1/2.2;
			png_get_gAMA(r_png_ptr, r_info_ptr, &file_gamma);
			gamma = TranscodingGammaCurve::Get(options.workingGamma, PowerLawGammaCurve::GetByEncodingGamma(file_gamma));
		}
#endif
		else
		{
			// no gamma info; PNG/W3C recommends to expect sRGB
			if (options.defaultGamma)
				gamma = TranscodingGammaCurve::Get(options.workingGamma, options.defaultGamma);
			else
				gamma = TranscodingGammaCurve::Get(options.workingGamma, SRGBGammaCurve::Get());
		}
	}

	// PNG is specified to use non-premultiplied alpha, so that's the preferred mode to use for the image container unless the user overrides
	// (e.g. to handle a non-compliant file).
	bool premul = false;
	if (options.premultiplyOverride)
		premul = options.premultiply;

	width = png_get_image_width(r_png_ptr, r_info_ptr);
	height = png_get_image_height(r_png_ptr, r_info_ptr);

	stride = 1;

	png_byte color_type = png_get_color_type(r_png_ptr, r_info_ptr);
	png_byte bit_depth = png_get_bit_depth(r_png_ptr, r_info_ptr);

	if (color_type == PNG_COLOR_TYPE_PALETTE)
	{
		// color palette image
		vector<Image::RGBAMapEntry> colormap ;
		Image::RGBAMapEntry entry;
		png_colorp palette;
		int cmap_len;
		png_get_PLTE(r_png_ptr, r_info_ptr, &palette, &cmap_len);
		bool has_alpha = png_get_valid(r_png_ptr, r_info_ptr, PNG_INFO_tRNS);
		png_bytep trans;
		int num_trans;
		png_get_tRNS(r_png_ptr, r_info_ptr, &trans, &num_trans, NULL);

		for(int index = 0; index < cmap_len; index++)
		{
			entry.red   = IntDecode(gamma, palette[index].red,   255);
			entry.green = IntDecode(gamma, palette[index].green, 255);
			entry.blue  = IntDecode(gamma, palette[index].blue,  255);
			entry.alpha = 1.0f ;
			if (has_alpha)
				if (index < num_trans)
					entry.alpha = IntDecode(trans[index], 255);
			colormap.push_back (entry);
		}

		Image::ImageDataType imagetype = options.itype;
		if (imagetype == Image::Undefined)
			imagetype = Image::Colour_Map;
		image = Image::Create (width, height, imagetype, colormap) ;
		image->SetPremultiplied(premul); // specify whether the color map data has premultiplied alpha
		gamma.reset(); // gamma has been taken care of by transforming the color table.

		// tell pnglib to expand data to 1 pixel/byte
		png_set_packing(r_png_ptr);
	}
	else if ((color_type == PNG_COLOR_TYPE_GRAY) && (bit_depth <= 8))
	{
		// grayscale image
		// (To keep the actual data reading code simple, we're pretending this to be a color palette image.)
		vector<Image::RGBAMapEntry> colormap ;
		Image::RGBAMapEntry entry;
		int cmap_len = 1 << bit_depth;
		bool has_alpha = png_get_valid(r_png_ptr, r_info_ptr, PNG_INFO_tRNS);
		png_bytep trans;
		int num_trans;
		png_get_tRNS(r_png_ptr, r_info_ptr, &trans, &num_trans, NULL);

		for(int index = 0; index < cmap_len; index++)
		{
			entry.red = entry.green = entry.blue = IntDecode(gamma, index, cmap_len - 1);
			entry.alpha = 1.0f ;
			if (has_alpha)
				if (index < num_trans)
					entry.alpha = IntDecode(trans[index], 255);
			colormap.push_back (entry);
		}

		Image::ImageDataType imagetype = options.itype;
		if (imagetype == Image::Undefined)
			imagetype = has_alpha ? Image::GrayA_Int8 : Image::Gray_Int8;
		image = Image::Create (width, height, imagetype, colormap) ;
		image->SetPremultiplied(premul); // specify whether the color map data has premultiplied alpha
		gamma.reset(); // gamma has been taken care of by transforming the color table.

		// tellg pnglib to expand data to 1 pixel/byte
		png_set_packing(r_png_ptr);
	}
	else if ((color_type & PNG_COLOR_MASK_COLOR) == PNG_COLOR_TYPE_GRAY)
	{
		// grayscale image
		stride = bit_depth <= 8 ? 1 : 2 ;
		if (color_type & PNG_COLOR_MASK_ALPHA)
			stride *= 2 ;
	}
	else if ((color_type == PNG_COLOR_TYPE_RGB) || (color_type == PNG_COLOR_TYPE_RGB_ALPHA))
	{
		// color image
		stride = color_type == PNG_COLOR_TYPE_RGB ? 3 : 4 ;
		if (bit_depth > 8)
			stride *= 2 ;
	}
	else
	{
		png_destroy_read_struct(&r_png_ptr, &r_info_ptr, (png_infopp)NULL);
		throw POV_EXCEPTION(kFileDataErr, "Unsupported color type in PNG image") ;
	}

	png_set_interlace_handling(r_png_ptr);

	if (ReadPNGUpdateInfo(r_png_ptr, r_info_ptr) == false)
	{
		png_destroy_read_struct(&r_png_ptr, &r_info_ptr, (png_infopp)NULL);
		if (messages.error.length() > 0)
			throw POV_EXCEPTION(kFileDataErr, messages.error.c_str());
		throw POV_EXCEPTION(kFileDataErr, "Cannot read PNG image.");
	}

	// Allocate row buffers for the input
	row_ptrs = new png_bytep [height];

	for(int row = 0; row < height; row++)
		row_ptrs[row] = new png_byte [png_get_rowbytes(r_png_ptr, r_info_ptr)];

	// Read in the entire image. we call a 'C' function for this as the PNG code
	// calls longjmp in the case of errors, and we'd rather keep that out of here.
	// NOTE: the above comment is probably out of date as of 20070325, but the
	// below code is still valid so there's no need to change it.
	if (ReadPNGImage (r_png_ptr, row_ptrs) == false)
	{
		for(int row = 0; row < height; row++)
			delete[] row_ptrs [row] ;
		delete[] row_ptrs;
		png_destroy_read_struct(&r_png_ptr, &r_info_ptr, (png_infopp)NULL);
		if (messages.error.length() > 0)
			throw POV_EXCEPTION(kFileDataErr, messages.error.c_str());
		throw POV_EXCEPTION(kFileDataErr, "Cannot read PNG image.");
	}

	// We must copy all the values because PNG supplies RGBRGB, but POV-Ray
	// stores RGB components in separate arrays
	if (image == NULL) // image will only be NULL at this point if the file is not a color-mapped type
	{
		bool has_alpha = (color_type & PNG_COLOR_MASK_ALPHA) != 0 ;

		if ((color_type & PNG_COLOR_MASK_COLOR) == PNG_COLOR_TYPE_GRAY)
		{
			// grayscale image
			// (note that although 8-bit greyscale images should have been handled earlier already, 8-bit greyscale + 8-bit alpha images haven't.)

			Image::ImageDataType imagetype = options.itype;

			if (imagetype == Image::Undefined)
			{
				if (GammaCurve::IsNeutral(gamma))
				{
					if (has_alpha)
						imagetype = bit_depth > 8 ? Image::GrayA_Int16 : Image::GrayA_Int8;
					else
						imagetype = bit_depth > 8 ? Image::Gray_Int16 : Image::Gray_Int8;
				}
				else
				{
					if (has_alpha)
						imagetype = bit_depth > 8 ? Image::GrayA_Gamma16 : Image::GrayA_Gamma8;
					else
						imagetype = bit_depth > 8 ? Image::Gray_Gamma16 : Image::Gray_Gamma8;
				}
			}

			image = Image::Create (width, height, imagetype);
			image->SetPremultiplied(premul); // set desired storage mode regarding alpha premultiplication
			if (bit_depth <= 8)
				image->TryDeferDecoding(gamma, 255); // try to have gamma adjustment being deferred until image evaluation.
			else
				image->TryDeferDecoding(gamma, 65535); // try to have gamma adjustment being deferred until image evaluation.

			if (has_alpha)
			{
				// with alpha channel
				if (bit_depth <= 8)
				{
					for(int row = 0; row < height; row++)
						for(int col = 0, j = 0; col < width; col++, j += stride)
							SetEncodedGrayAValue (image, col, row, gamma, 255, (unsigned int) row_ptrs[row][j], row_ptrs[row][j + 1], premul) ;
				}
				else
				{
					for(int row = 0; row < height; row++)
					{
						for(int col = j = 0; col < width; col++, j += stride)
						{
							unsigned int c = ((unsigned short)row_ptrs[row][j] << 8) | row_ptrs[row][j + 1];
							unsigned int a = (((unsigned short)row_ptrs[row][j + 2] << 8) | row_ptrs[row][j + 3]);
							SetEncodedGrayAValue (image, col, row, gamma, 65535, c, a, premul) ;
						}
					}
				}
			}
			else
			{
				// without alpha channel
				if (bit_depth <= 8)
				{
					for(int row = 0; row < height; row++)
						for(int col = j = 0; col < width; col++, j += stride)
							SetEncodedGrayValue (image, col, row, gamma, 255, (unsigned int) row_ptrs[row][j]) ;
				}
				else
				{
					for(int row = 0; row < height; row++)
						for(int col = j = 0; col < width; col ++, j += stride)
							SetEncodedGrayValue (image, col, row, gamma, 65535, ((unsigned int)row_ptrs[row][j] << 8) | row_ptrs[row][j + 1]) ;
				}
			}
		}
		else
		{
			// color image ((color_type & PNG_COLOR_MASK_COLOR) != 0)
			Image::ImageDataType imagetype = options.itype;

			if (imagetype == Image::Undefined)
			{
				if (GammaCurve::IsNeutral(gamma))
				{
					if (has_alpha)
						imagetype = bit_depth > 8 ? Image::RGBA_Int16 : Image::RGBA_Int8;
					else
						imagetype = bit_depth > 8 ? Image::RGB_Int16 : Image::RGB_Int8;
				}
				else
				{
					if (has_alpha)
						imagetype = bit_depth > 8 ? Image::RGBA_Gamma16 : Image::RGBA_Gamma8;
					else
						imagetype = bit_depth > 8 ? Image::RGB_Gamma16 : Image::RGB_Gamma8;
				}
			}

			image = Image::Create (width, height, imagetype);
			image->SetPremultiplied(premul); // set desired storage mode regarding alpha premultiplication
			if (bit_depth <= 8)
				image->TryDeferDecoding(gamma, 255); // try to have gamma adjustment being deferred until image evaluation.
			else
				image->TryDeferDecoding(gamma, 65535); // try to have gamma adjustment being deferred until image evaluation.

			if (bit_depth <= 8)
			{
				for(int row = 0; row < height; row++)
				{
					for(int col = j = 0; col < width; col++, j += stride)
					{
						unsigned int r = row_ptrs[row][j];
						unsigned int g = row_ptrs[row][j + 1];
						unsigned int b = row_ptrs[row][j + 2];
						if (has_alpha)
							SetEncodedRGBAValue (image, col, row, gamma, 255, r, g, b, row_ptrs[row][j + 3], premul);
						else
							SetEncodedRGBValue (image, col, row, gamma, 255, r, g, b);
					}
				}
			}
			else
			{
				for(int row = 0; row < height; row++)
				{
					for(int col = j = 0; col < width; col++, j += stride)
					{
						unsigned int r = ((unsigned int)row_ptrs[row][j] << 8) | row_ptrs[row][j + 1];
						unsigned int g = ((unsigned int)row_ptrs[row][j + 2] << 8) | row_ptrs[row][j + 3];
						unsigned int b = ((unsigned int)row_ptrs[row][j + 4] << 8) | row_ptrs[row][j + 5];
						if (has_alpha)
							SetEncodedRGBAValue (image, col, row, gamma, 65535, r, g, b, (((unsigned int)row_ptrs[row][j + 6] << 8) | row_ptrs[row][j + 7]), premul) ;
						else
							SetEncodedRGBValue (image, col, row, gamma, 65535, r, g, b) ;
					}
				}
			}
		}
	}
	else
	{
		// grayscale palette image or color palette image
		for (int row = 0; row < height; row++)
			for (int col = j = 0; col < width; col++, j += stride)
				image->SetIndexedValue (col, row, row_ptrs [row] [j]) ;
	}

	// Clean up the rest of the PNG memory and such
	for(int row = 0; row < height; row++)
		delete[] row_ptrs [row] ;
	delete[] row_ptrs;

	// clean up after the read, and free any memory allocated
	png_destroy_read_struct(&r_png_ptr, &r_info_ptr, (png_infopp)NULL);

	if (messages.error.length() > 0)
		throw POV_EXCEPTION(kFileDataErr, messages.error.c_str());

	options.warnings = messages.warnings ;
	return (image) ;
}

void Write (OStream *file, const Image *image, const Image::WriteOptions& options)
{
	int             himask;
	int             png_stride;
	int             width = image->GetWidth() ;
	int             height = image->GetHeight() ;
	int             j;
	int             bpcc = options.bpcc;
	bool            use_alpha = image->HasTransparency() && options.alphachannel;
	unsigned int    color;
	unsigned int    alpha;
	unsigned int    r;
	unsigned int    g;
	unsigned int    b;
	unsigned int    maxValue;
	unsigned int    hiShift;
	unsigned int    loShift;
	png_info        *info_ptr = NULL;
	png_struct      *png_ptr  = NULL;
	Messages        messages;
	GammaCurvePtr   gamma;
	Metadata        meta;
	DitherHandler*  dither = options.dither.get();

	if (options.encodingGamma)
		gamma = TranscodingGammaCurve::Get(options.workingGamma, options.encodingGamma);
	else
		// PNG/W3C recommends to use sRGB color space
		gamma = TranscodingGammaCurve::Get(options.workingGamma, SRGBGammaCurve::Get());

	// PNG is specified to use non-premultiplied alpha, so that's the way we do it unless the user overrides
	// (e.g. to handle a non-compliant file).
	bool premul = false;
	if (options.premultiplyOverride)
		premul = options.premultiply;

	if (bpcc == 0)
		bpcc = image->GetMaxIntValue() == 65535 ? 16 : 8 ;
	else if (bpcc < 5)
		bpcc = 5 ;
	else if (bpcc > 16)
		bpcc = 16 ;

	// special case: if options.grayscale is set, we enforce 16bpp irregardless of other settings
	if (options.grayscale)
		bpcc = 16;

	maxValue = (1<<bpcc)-1;

	if ((png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, (png_voidp)(&messages), png_pov_err, png_pov_warn)) == NULL)
		throw POV_EXCEPTION(kOutOfMemoryErr, "Cannot allocate PNG data structures");
	if ((info_ptr = png_create_info_struct(png_ptr)) == NULL)
		throw POV_EXCEPTION(kOutOfMemoryErr, "Cannot allocate PNG data structures");

	if (setjmp(png_jmpbuf(png_ptr)))
	{
		// If we get here, we had a problem writing the file
		png_destroy_write_struct(&png_ptr, &info_ptr);
		throw POV_EXCEPTION(kFileDataErr, "Error writing PNG file") ;
	}

	// Set up the compression structure
	png_set_write_fn (png_ptr, file, png_pov_write_data, png_pov_flush_data);

	bool use_color = !(image->IsGrayscale() | options.grayscale);

	// Fill in the relevant image information
	png_set_IHDR(png_ptr, info_ptr,
	             width, height,
	             8 * ((bpcc + 7) / 8), // bit_depth
	             (use_color ? PNG_COLOR_MASK_COLOR : 0) | (use_alpha ? PNG_COLOR_MASK_ALPHA : 0), // color_type
	             PNG_INTERLACE_NONE,
	             PNG_COMPRESSION_TYPE_DEFAULT,
	             PNG_FILTER_TYPE_DEFAULT // interlace_method
	             );

#if defined(PNG_WRITE_sBIT_SUPPORTED)
	png_color_8 sbit = {0,0,0,0,0};
	if (use_color)
		sbit.red = sbit.green = sbit.blue = bpcc;
	else
		sbit.gray = bpcc;
	if (use_alpha)
		sbit.alpha = bpcc;
	png_set_sBIT(png_ptr, info_ptr, &sbit);
#endif // PNG_WRITE_sBIT_SUPPORTED

#if defined(PNG_WRITE_gAMA_SUPPORTED)
	png_set_gAMA(png_ptr, info_ptr, 1.0f / (options.workingGamma->ApproximateDecodingGamma() * gamma->ApproximateDecodingGamma()));
#endif // PNG_WRITE_gAMA_SUPPORTED

#if defined(PNG_WRITE_sRGB_SUPPORTED)
	if (options.encodingGamma && options.encodingGamma->GetTypeId() == kPOVList_GammaType_SRGB)
		// gamma curve is sRGB transfer function; pretend that color space also matches sRGB
		png_set_sRGB(png_ptr, info_ptr, PNG_sRGB_INTENT_PERCEPTUAL); // we have to write *some* value; perceptual will probably be the most common
#endif // PNG_WRITE_gAMA_SUPPORTED

#if defined(PNG_WRITE_oFFs_SUPPORTED)
	png_set_oFFs(png_ptr, info_ptr, options.offset_x, options.offset_y, PNG_OFFSET_PIXEL);
#endif // PNG_WRITE_oFFs_SUPPORTED

#if defined(PNG_WRITE_tIME_SUPPORTED)
	png_time timestamp;
	timestamp.year   = meta.getYear();
	timestamp.month  = meta.getMonth();
	timestamp.day    = meta.getDay();
	timestamp.hour   = meta.getHour();
	timestamp.minute = meta.getMin();
	timestamp.second = meta.getSec();
	png_set_tIME(png_ptr, info_ptr, &timestamp);
#endif // PNG_WRITE_tIME_SUPPORTED

#if defined(PNG_WRITE_TEXT_SUPPORTED)
	/* Line feed is "local" */
	string comment=string("Render Date: ") + meta.getDateTime() + "\n";
	if (!meta.getComment1().empty())
		comment += meta.getComment1() + "\n";
	if (!meta.getComment2().empty())
		comment += meta.getComment2() + "\n";
	if (!meta.getComment3().empty())
		comment += meta.getComment3() + "\n";
	if (!meta.getComment4().empty())
		comment += meta.getComment4() + "\n";
	string soft (meta.getSoftware());
	png_text p_text[2] = {
		{ PNG_TEXT_COMPRESSION_NONE, const_cast<char *>("Software"), const_cast<char *>(soft.c_str()),    soft.length() },
		{ PNG_TEXT_COMPRESSION_NONE, const_cast<char *>("Comment"),  const_cast<char *>(comment.c_str()), comment.length() },
	};
	png_set_text(png_ptr, info_ptr, p_text, 2);
#endif // PNG_WRITE_TEXT_SUPPORTED

	png_write_info(png_ptr, info_ptr);
	png_stride = use_color ? 3 : 1;
	if (use_alpha)
		png_stride++;
	png_stride *= (bpcc + 7) / 8;

	boost::scoped_array<png_byte> row_ptr (new png_byte [width*png_stride]);

	for (int row = 0 ; row < height ; row++)
	{
		/*
		* We must copy all the values because PNG expects RGBRGB bytes, but
		* POV-Ray stores RGB components in separate arrays as floats.  In
		* order to use the full scale values at the lower bit depth, PNG
		* recommends filling the low-order bits with a copy of the high-order
		* bits.  However, studies have shown that filling the low order bits
		* with constant bits significantly improves compression, which we're
		* doing here.  Note that since the true bit depth is stored in the
		* sBIT chunk, the extra packed bits are not important.
		*/

		switch (bpcc)
		{
			case 5:
			case 6:
			case 7:
				// Handle shifting for arbitrary output bit depth
				hiShift = 8 - bpcc;
				loShift = 2*bpcc - 8;
				if (use_color)
				{
					for (int col = j = 0; col < width; col++, j += png_stride)
					{
						if (use_alpha)
						{
							GetEncodedRGBAValue (image, col, row, gamma, maxValue, r, g, b, alpha, *dither, premul);
							row_ptr[j + 3] = alpha << hiShift;
							row_ptr[j + 3] |= alpha >> loShift;
						}
						else
							GetEncodedRGBValue (image, col, row, gamma, maxValue, r, g, b, *dither);

						row_ptr[j] = r << hiShift;
						row_ptr[j] |= r >> loShift;

						row_ptr[j+1] = g << hiShift;
						row_ptr[j+1] |= g >> loShift;

						row_ptr[j+2] = b << hiShift;
						row_ptr[j+2] |= b >> loShift;
					}
				}
				else
				{
					for (int col = j = 0; col < width; col++, j += png_stride)
					{
						if (use_alpha)
						{
							GetEncodedGrayAValue (image, col, row, gamma, maxValue, color, alpha, *dither, premul);
							row_ptr[j + 1] = alpha << hiShift;
							row_ptr[j + 1] |= alpha >> loShift;
						}
						else
							color = GetEncodedGrayValue (image, col, row, gamma, maxValue, *dither) ;

						// Use left-bit replication (LBR) for bit depths < 8
						row_ptr[j] = color << hiShift;
						row_ptr[j] |= color >> loShift;
					}
				}
				break;

			case 8:
				if (use_color)
				{
					for (int col = j = 0; col < width; col++, j += png_stride)
					{
						if (use_alpha)
						{
							GetEncodedRGBAValue (image, col, row, gamma, maxValue, r, g, b, alpha, *dither, premul);
							row_ptr[j + 3] = alpha;
						}
						else
							GetEncodedRGBValue (image, col, row, gamma, maxValue, r, g, b, *dither) ;
						row_ptr[j] = r;
						row_ptr[j + 1] = g;
						row_ptr[j + 2] = b;
					}
				}
				else
				{
					for (int col = j = 0; col < width; col++, j += png_stride)
					{
						if (use_alpha)
						{
							GetEncodedGrayAValue (image, col, row, gamma, maxValue, color, alpha, *dither, premul);
							row_ptr[j + 1] = alpha;
						}
						else
							color = GetEncodedGrayValue (image, col, row, gamma, maxValue, *dither) ;
						row_ptr[j] = color;
					}
				}
				break;

			case 16:
				if (use_color)
				{
					for (int col = j = 0; col < width; col++, j += png_stride)
					{
						if (use_alpha)
						{
							GetEncodedRGBAValue (image, col, row, gamma, maxValue, r, g, b, alpha, *dither, premul);
							row_ptr[j+6] = alpha >> 8;
							row_ptr[j+7] = alpha & 0xff;
						}
						else
							GetEncodedRGBValue (image, col, row, gamma, maxValue, r, g, b, *dither) ;

						row_ptr[j] = r >> 8;
						row_ptr[j + 1] = r & 0xFF;

						row_ptr[j + 2] = g >> 8;
						row_ptr[j + 3] = g & 0xFF;

						row_ptr[j + 4] = b >> 8;
						row_ptr[j + 5] = b & 0xFF;
					}
				}
				else
				{
					for (int col = j = 0; col < width; col++, j += png_stride)
					{
						if (use_alpha)
						{
							GetEncodedGrayAValue (image, col, row, gamma, maxValue, color, alpha, *dither, premul);
							row_ptr[j+2] = alpha >> 8;
							row_ptr[j+3] = alpha & 0xff;
						}
						else
							color = GetEncodedGrayValue (image, col, row, gamma, maxValue, *dither) ;
						row_ptr[j] = color >> 8;
						row_ptr[j+1] = color & 0xff;
					}
				}
				break;

			default:  // bpcc 9 - 15
				// Handle shifting for arbitrary output bit depth
				hiShift = 16 - bpcc;
				loShift = 2*bpcc - 16;
				himask = 0xFF ^ ((1 << hiShift) - 1);
				if (use_color)
				{
					for (int col = j = 0; col < width; col++, j += png_stride)
					{
						if (use_alpha)
						{
							GetEncodedRGBAValue (image, col, row, gamma, maxValue, r, g, b, alpha, *dither, premul);
							row_ptr[j + 6] = alpha >> (8 - hiShift);
							row_ptr[j + 7] = alpha << hiShift;
							row_ptr[j + 7] |= alpha >> loShift;
						}
						else
							GetEncodedRGBValue (image, col, row, gamma, maxValue, r, g, b, *dither) ;

						row_ptr[j] = r >> (8 - hiShift);
						row_ptr[j + 1] = r << hiShift;
						row_ptr[j + 1] |= r >> loShift;

						row_ptr[j + 2] = g >> (8 - hiShift);
						row_ptr[j + 3] = g << hiShift;
						row_ptr[j + 3] |= g >> loShift;

						row_ptr[j + 4] = b >> (8 - hiShift);
						row_ptr[j + 5] = b << hiShift;
						row_ptr[j + 5] |= b >> loShift;
					}
				}
				else
				{
					for (int col = j = 0; col < width; col++, j += png_stride)
					{
						if (use_alpha)
						{
							GetEncodedGrayAValue (image, col, row, gamma, maxValue, color, alpha, *dither, premul);
							row_ptr[j + 2] = alpha >> (8 - hiShift);
							row_ptr[j + 3] = alpha << hiShift;
							row_ptr[j + 3] |= alpha >> loShift;
						}
						else
							color = GetEncodedGrayValue (image, col, row, gamma, maxValue, *dither) ;

						row_ptr[j] = color >> (8 - hiShift);
						row_ptr[j + 1] = color << hiShift;
						row_ptr[j + 1] |= color >> loShift;
					}
				}
		}

		if (setjmp(png_jmpbuf(png_ptr)))
		{
			if (messages.error.length() > 0)
				throw POV_EXCEPTION(kFileDataErr, messages.error.c_str());

			// If we get here, we had a problem writing the file
			throw POV_EXCEPTION(kFileDataErr, "Cannot write PNG output data");
		}

		// Write out a scanline
		png_write_row (png_ptr, row_ptr.get());
	}

	if (messages.error.length() > 0)
		throw messages.error.c_str();

	png_write_end(png_ptr, info_ptr);
	png_destroy_write_struct(&png_ptr, &info_ptr);
}

} // end of namespace Png

}

#endif  // LIBPNG_MISSING