Imported from libpng-0.86.tar

build.bat

@@ -1,2 +0,0 @@
-make -fmakefile.bor -B -DMODEL=m %1 %2 %3 libpng >buildm.out
-make -fmakefile.bor -B -DMODEL=l %1 %2 %3 libpng >buildl.out

example.c

@@ -79,9 +79,17 @@ void read_png(char *file_name)
    png_info_init(info_ptr);
    png_read_init(png_ptr);
 
-   /* set up the input control */
+   /* set up the input control if you are using standard C streams */
    png_init_io(png_ptr, fp);
 
+	/* if you are using replacement read functions, here you would call */
+	png_set_read_fn(png_ptr, (void *)io_ptr, user_read_fn);
+	/* where io_ptr is a structure you want available to the callbacks */
+
+	/* if you are using replacement message functions, here you would call */
+	png_set_message_fn(png_ptr, (void *)msg_ptr, user_error_fn, user_warning_fn);
+	/* where msg_ptr is a structure you want available to the callbacks */
+
 	/* read the file information */
 	png_read_info(png_ptr, info_ptr);
 
@@ -262,7 +270,7 @@ initialize_png_reader()
 		function callbacks, even if you aren't using them all.
 		You can put a void pointer in place of the NULL, and
 		retrieve the pointer from inside the callbacks using
-		the function png_get_msg_ptr(png_ptr); */
+		the function png_get_progressive_ptr(png_ptr); */
 	png_set_progressive_read_fn(png_ptr, NULL,
 		info_callback, row_callback, end_callback);
 
@@ -386,9 +394,17 @@ void write_png(char *file_name, ... other image information ...)
    png_info_init(info_ptr);
    png_write_init(png_ptr);
 
-   /* set up the output control */
+   /* set up the output control if you are using standard C streams */
    png_init_io(png_ptr, fp);
 
+	/* if you are using replacement write functions, here you would call */
+	png_set_write_fn(png_ptr, (void *)io_ptr, user_write_fn, user_flush_fn);
+	/* where io_ptr is a structure you want available to the callbacks */
+
+	/* if you are using replacement message functions, here you would call */
+	png_set_message_fn(png_ptr, (void *)msg_ptr, user_error_fn, user_warning_fn);
+	/* where msg_ptr is a structure you want available to the callbacks */
+
 	/* set the file information here */
    info_ptr->width = ;
    info_ptr->height = ;
@@ -402,9 +418,17 @@ void write_png(char *file_name, ... other image information ...)
 
    /* optional significant bit chunk */
    info_ptr->valid |= PNG_INFO_sBIT;
-   info_ptr->sig_bit = true_bit_depth;
+	/* if we are dealing with a grayscale image then */
+	info_ptr->sig_bit.gray = true_bit_depth;
+	/* otherwise, if we are dealing with a color image then */
+	info_ptr->sig_bit.red = true_red_bit_depth;
+	info_ptr->sig_bit.green = true_green_bit_depth;
+	info_ptr->sig_bit.blue = true_blue_bit_depth;
+	/* if the image has an alpha channel then */
+   info_ptr->sig_bit.alpha = true_alpha_bit_depth;
   
-   /* optional gamma chunk */
+	/* optional gamma chunk is strongly suggested if you have any guess
+	   as to the correct gamma of the image */
 	info_ptr->valid |= PNG_INFO_gAMA;
    info_ptr->gamma = gamma;
 

libpng.txt

@@ -1,23 +1,29 @@
 libpng.txt - a description on how to use and modify libpng
 
-   libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
 	For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-	December 19, 1995
+	January 10, 1996
+	Updated/rewritten per request in the libpng FAQ
+	Copyright (c) 1995 Frank J. T. Wojcik
+	December 18, 1995
+
+I. Introduction
 
 This file describes how to use and modify the PNG reference library
-(known as libpng) for your own use.  There are four sections to this
+(known as libpng) for your own use.  There are five sections to this
-file: reading, writing, modifying, and configuration notes for various
+file: introduction, structures, reading, writing, and modification and
-special platforms.  Other then this file, the file example.c is a good
+configuration notes for various special platforms.  Other then this
-starting point for using the library, as it is heavily commented and
+file, example.c is a good starting point for using the library, as
-should include everything most people will need.
+it is heavily commented and should include everything most people
+will need.
 
 Libpng was written as a companion to the PNG specification, as a
 way to reduce the amount of time and effort it takes to support
 the PNG file format in application programs.  Most users will not
 have to modify the library significantly; advanced users may want
-to modify it more.  The library was coded for both users.  All
+to modify it more.  The library was coded for both kind of users.
-attempts were made to make it as complete as possible, while
+All attempts were made to make it as complete as possible, while
 keeping the code easy to understand.  Currently, this library
 only supports C.  Support for other languages is being considered.
 
@@ -31,16 +37,12 @@ majority of the needs of it's users.
 
 Libpng uses zlib for its compression and decompression of PNG files.
 The zlib compression utility is a general purpose utility that is
-useful for more then PNG files, and can be used without libpng for
+useful for more then PNG files, and can be used without libpng.
-whatever use you want.  See the documentation delivered with zlib for
+See the documentation delivered with zlib for more details.
-more details.
 
-Those people who do not need to modify libpng should still read at
-least part of the PNG specification.  The most important parts are
-the data formats and the chunk descriptions.  Those who will be
-making changes to libpng should read the whole specification.
 
-The structures:
+
+II. Structures
 
 There are two main structures that are important to libpng, png_struct
 and png_info.  The first, png_struct, is an internal structure that
@@ -48,19 +50,24 @@ will not, for the most part, be used by the general user except as
 the first variable passed to every png function call.
 
 The png_info structure is designed to provide information about the
-png file.  All of it's fields are intended to be examined or modified
+png file.  All of its fields are intended to be examined or modified
 by the user.  See png.h for a good description of the png_info fields.
+png.h is also an invaluable reference for programming with libpng.
 
 And while I'm on the topic, make sure you include the png header file:
 
 #include <png.h>
 
+
+
+III. Reading
+
 Checking PNG files:
 
-Libpng provides a simple check to see if a file is a png file.  To
+Libpng provides a simple check to see if a file is a PNG file.  To
 use it, pass in the first 1 to 8 bytes of the file, and it will return
 true or false (1 or 0) depending on whether the bytes could be part
-of a png file.  Of course, the more bytes you pass in, the greater
+of a PNG file.  Of course, the more bytes you pass in, the greater
 the accuracy of the prediction.  If you pass in more then eight bytes,
 libpng will only look at the first eight bytes.
 
@@ -69,14 +76,17 @@ libpng will only look at the first eight bytes.
 
 Reading PNG files:
 
-This section covers reading png files row by row.  Progressive reading
+We'll now walk you through the possible functions to call when reading
-is covered in the next section (although you still need to read this
+in a PNG file, briefly explaining the syntax and purpose of each one.
-section, as much of the information is still needed).
+See example.c and png.h for more detail.  While Progressive reading
+is covered in the next section, you will still need some of the
+functions discussed in this section to read a PNG file.
 
-The first thing you need to do while reading a PNG file is to allocate
+The first thing you need to do while reading a PNG file, aside from
-and initialize png_struct and png_info.  As these are both large, you
+the standard I/O initialization, is to allocate and initialize
-may not want to store these on the stack, unless you have stack space
+png_struct and png_info.  As these are both large, you may not want to
-to spare.  Of course, you will want to check if malloc returns NULL.
+store these on the stack, unless you have stack space to spare.  Of
+course, you will want to check if malloc returns NULL.
 
 	png_structp png_ptr = malloc(sizeof (png_struct));
 	if (!png_ptr)
@@ -100,6 +110,10 @@ much to undo.
 		return;
 	}
 
+If you are not using the standard i/o functions, you will need
+to replace them with custom functions.  See the discussion under
+Customizing libpng.
+
 After you have these structures, you will need to set up the
 error handling.  When libpng encounters an error, it expects to
 longjmp back to your routine.  Therefore, you will need to call
@@ -108,8 +122,8 @@ read the file from different routines, you will need to update
 the jmpbuf field every time you enter a new routine that will
 call a png_ function.  See your documentation of setjmp/longjmp
 for your compiler for more information on setjmp/longjmp.  See
-the discussion on png error handling in the Customizing Libpng
+the discussion on libpng error handling in the Customizing Libpng
-section below for more information on the png error handling.
+section below for more information on the libpng error handling.
 If an error occurs, and libpng longjmp's back to your setjmp,
 you will want to call png_read_destroy() to free any memory.
 
@@ -123,7 +137,7 @@ you will want to call png_read_destroy() to free any memory.
 		return;
 	}
 
-Next, you will need to call png_read_init() and png_info_init().
+Next, you will need to call png_info_init() and png_read_init().
 These functions make sure all the fields are initialized to useful
 values, and, in the case of png_read_init(), and allocate any memory
 needed for internal uses.  You must call png_info_init() first, as
@@ -150,28 +164,44 @@ image data.  You do this with a call to png_read_info().
 
 The png_info structure is now filled in with all the data necessary
 to read the file.  Some of the more important parts of the png_info are:
+
 	width          - holds the width of the file
 	height         - holds the height of the file
 	bit_depth      - holds the bit depth of one of the image channels
 	color_type     - describes the channels and what they mean
-      see the PNG_COLOR_TYPE_ macros for more information
+						  (see the PNG_COLOR_TYPE_ macros for more information)
 	channels       - number of channels of info for the color type
-   pixel_depth - bits per pixel
+	pixel_depth    - bits per pixel, the result of multiplying the bit_depth
+						  times the channels
 	rowbytes       - number of bytes needed to hold a row
 	interlace_type - currently 0 for none, 1 for interlaced
-	valid - this details which optional chunks were found in the file
+	valid          - this details which optional chunks were found in the
-		to see if a chunk was present, OR valid with the appropriate
+						  file to see if a chunk was present, AND valid with the
-      PNG_INFO_<chunk name> define.
+						  appropriate PNG_INFO_<chunk name> define.
-   palette and num_palette - the palette for the file
+
+These are also important, but their validity depends on whether a
+corresponding chunk exists. Use valid (see above) to ensure that what
+you're doing with these values makes sense.
+
+	palette        - the palette for the file
+	num_palette    - number of entries in the palette
 	gamma          - the gamma the file is written at
-   sig_bit and sig_bit_number - the number of significant bits
+	sig_bit        - the number of significant bits
-   trans, trans_values, and number_trans - transparency info
+						  for the gray, red, green, and blue channels, whichever are
+						  appropriate for the given color type.
+	sig_bit_number - number of channels
+	trans_values   - transparent pixel for non-paletted images
+	trans          - array of transparent entries for paletted images
+	number_trans   - number of transparent entries
 	hist           - histogram of palette
-   text and num_text - text comments in the file.
+	text           - text comments in the file.
+	num_text       - number of comments
+
 for more information, see the png_info definition in png.h and the
 PNG specification for chunk contents.  Be careful with trusting
 rowbytes, as some of the transformations could increase the space
 needed to hold a row (expand, rgbx, xrgb, graph_to_rgb, etc.).
+See png_update_info(), below.
 
 A quick word about text and num_text.  PNG stores comments in
 keyword/text pairs, one pair per chunk.  While there are
@@ -183,8 +213,8 @@ See the png specification for more details.  There is no requirement
 to have text after the keyword.
 
 Keywords are restricted to 80 characters without leading or trailing
-spaces, but spaces are allowed within the keyword  Nothing
+spaces, but spaces are allowed within the keyword  It is possible to
-prevents you from duplicating the keyword.  The text field is an
+have the same keyword any number of times.  The text field is an
 array of png_text structures, each holding pointer to a keyword
 and a pointer to a text string.  Only the text string may be null.
 The keyword/text pairs are put into the array in the order that
@@ -204,7 +234,7 @@ check to see if it has data that it can do somthing with, you should
 make sure to only enable a transformation if it will be valid for
 the data.  For example, don't swap red and blue on grayscale data.
 
-This transforms bit depths of less then 8 to 8 bits, changes paletted
+This transforms bit depths of less than 8 to 8 bits, changes paletted
 images to rgb, and adds an alpha channel if there is transparency
 information in a tRNS chunk.  This is probably most useful on grayscale
 images with bit depths of 2 or 4 and tRNS chunks.
@@ -243,7 +273,8 @@ This handles gamma transformations of the data.  Pass both the file
 gamma and the desired screen gamma.  If the file does not have a
 gamma value, you can pass one anyway if you wish.  Note that file
 gammas are inverted from screen gammas.  See the discussions on
-gamma in the PNG specification for more information.
+gamma in the PNG specification for more information.  It is strongly
+recommended that viewers support gamma correction.
 
    if (info_ptr->valid & PNG_INFO_gAMA)
       png_set_gamma(png_ptr, screen_gamma, info_ptr->gamma);
@@ -256,16 +287,19 @@ PNG can have files with 16 bits per channel.  If you only can handle
    if (info_ptr->bit_depth == 16)
       png_set_strip_16(png_ptr);
 
-If you need to reduce an rgb file to a paletted file, or if a
+If you need to reduce an rgb file to a paletted file (perhaps because
-paletted file has more entries then will fit on your screen, this
+a paletted file has more entries then will fit on your screen)
-function will do that.  Note that this is a simple match dither, that
+png_set_dither() will do that.  Note that this is a simple match
-merely finds the closest color available.  This should work fairly
+dither, that merely finds the closest color available.  This should
-well with optimized palettes, and fairly badly with linear color
+work fairly well with optimized palettes, and fairly badly with linear
-cubes.  If you pass a palette that is larger then maximum_colors,
+color cubes.  If you pass a palette that is larger then
-the file will reduce the number of colors in the palette so it
+maximum_colors, the file will reduce the number of colors in the
-will fit into maximum_colors.  If there is an histogram, it will
+palette so it will fit into maximum_colors.  If there is a histogram,
-use it to make intelligent choises when reducing the palette.  If
+it will use it to make intelligent choices when reducing the palette.
-there is no histogram, it may not do a good job.
+If there is no histogram, it may not do as good a job.
+
+This function will be rewritten and/or replaced in libpng 0.9, which
+will have full two pass dithering with optimized palettes.
 
 	if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
    {
@@ -283,53 +317,54 @@ there is no histogram, it may not do a good job.
       }
    }
 
-PNG files describe monocrome as black is zero and white is one.  If you
+PNG files describe monocrome as black is zero and white is one.  The
-want this reversed (black is one and white is zero), call this:
+following code will reverse this (make black be one and white be zero):
 
    if (info_ptr->bit_depth == 1 &&
       info_ptr->color_type == PNG_COLOR_GRAY)
       png_set_invert(png_ptr);
 
-PNG files reduce possible bit depths to 1, 2, 4, 8, and 16.  However,
+PNG files have possible bit depths of 1, 2, 4, 8, and 16.  However,
 they also provide a way to describe the true bit depth of the image.
-Then they require bits to be scaled to full range for the bit depth
+It is then required that values be "scaled" or "shifted" up to the bit
-used in the file.  If you want to reduce your pixels back down to
+depth used in the file.  See the PNG specification for details.  This
-the true bit depth, call this:
+code reduces the pixels back down to the true bit depth:
 
 	if (info_ptr->valid & PNG_INFO_sBIT)
 		png_set_shift(png_ptr, &(info_ptr->sig_bit));
 
 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
-they can, resulting in, for example, 8 pixels per byte for 1 bit files.
+they can, resulting in, for example, 8 pixels per byte for 1 bit
-If you would rather these were expanded to 1 pixel per byte without
+files.  This code expands to 1 pixel per byte without changing the
-changing the values of the pixels, call this:
+values of the pixels:
 
 	if (info_ptr->bit_depth < 8)
 		png_set_packing(png_ptr);
 
-PNG files store 3 color pixels in red, green, blue order.  If you would
+PNG files store 3 color pixels in red, green, blue order.  This code
-rather have the pixels as blue, green, red, call this.
+changes the storage of the pixels to blue, green, red:
 
 	if (info_ptr->color_type == PNG_COLOR_TYPE_RGB ||
 		info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
 		png_set_bgr(png_ptr);
 
-For some uses, you may want a grayscale image to be represented as
+For some uses, you may want a gray-scale image to be represented as
-rgb.  If you need this, call this:
+rgb.  This code will do that conversion:
 
    if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY ||
       info_ptr->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
 		png_set_gray_to_rgb(png_ptr);
 
-PNG files store 16 bit pixels in network byte order (most significant
+PNG files store 16 bit pixels in network byte order (big-endian,
-bit first).  If you would rather store them the other way, (the way
+ie. most significant bits first).  This code chages the storage to the
-PC's store them, for example), call this:
+other way (little-endian, ie. least significant bits first, eg. the
+way PCs store them):
 
 	if (info_ptr->bit_depth == 16)
 		png_set_swap(png_ptr);
 
-PNG files store rgb pixels packed into 3 bytes.  If you would rather
+PNG files store rgb pixels packed into 3 bytes. This code packs them
-pack them into 4 bytes, call this:
+into 4 bytes:
 
    if (info_ptr->bit_depth == 8 &&
       info_ptr->color_type == PNG_COLOR_TYPE_RGB)
@@ -339,8 +374,8 @@ where filler_byte is the number to fill with, and the location is
 either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
 you want the filler before the rgb or after.
 
-Finally, if you need the interlacing as discussed below, call
+The last thing to handle is interlacing; this is covered in detail below,
-this here:
+but you must call the function here.
 
    if (info_ptr->interlace_type)
       number_passes = png_set_interlace_handling(png_ptr);
@@ -353,10 +388,10 @@ before it reads the first row.
 
 	png_start_read_image(png_ptr);
 
-If you want, libpng will update your png_info structure to reflect
+libpng can update your png_info structure to reflect any
-any transformations you've requested with this call.  This is most
+transformations you've requested with this call.  This is most useful
-useful to update the info structures rowbytes field, so you can
+to update the info structures rowbytes field, so you can use it to
-use it to allocate your image memory.  This function calls
+allocate your image memory.  This function calls
 png_start_read_image(), so you don't have to call both of them.
 
 	png_read_update_info(png_ptr, info_ptr);
@@ -402,20 +437,21 @@ row_pointers:
 
 	png_read_rows(png_ptr, &row_pointers, NULL, 1);
 
-When the file is interlaced (info_ptr->interlace_type == 1), things
+If the file is interlaced (info_ptr->interlace_type != 0), things get
-get a good deal harder.  PNG files have a complicated interlace scheme
+a good deal harder.  The only currently (as of 12/95) defined
-that breaks down an image into seven smaller images of varying size.
+interlacing scheme for PNG files (info_ptr->interlace_type == 1) is a
-Libpng will fill out those images if you want, or it will give them
+complicated interlace scheme, known as Adam7, that breaks down an
-to you "as is".  If you want to fill them out, there is two ways
+image into seven smaller images of varying size.  libpng will fill out
-to do that.  The one mentioned in the PNG specification is to expand
+those images or it will give them to you "as is".  If you want to fill
-each pixel to cover those pixels that have not been read yet.  This
+them out, there are two ways to do that.  The one mentioned in the PNG
-results in a blocky image for the first pass, which gradually smooths
+specification is to expand each pixel to cover those pixels that have
-out as more pixels are read.  The other method is the "sparkle" method,
+not been read yet.  This results in a blocky image for the first pass,
-where pixels are draw only in their final locations, with the rest of
+which gradually smoothes out as more pixels are read.  The other
-the image remaining whatever colors they were initialized to before
+method is the "sparkle" method, where pixels are draw only in their
-the start of the read.  The first method usually looks better, but
+final locations, with the rest of the image remaining whatever colors
-tends to be slower, as there are more pixels to put in the rows.  Some
+they were initialized to before the start of the read.  The first
-examples to help clear this up:
+method usually looks better, but tends to be slower, as there are more
+pixels to put in the rows.
 
 If you don't want libpng to handle the interlacing details, just
 call png_read_rows() the correct number of times to read in all
@@ -513,10 +549,10 @@ initialize_png_reader()
 
 	/* this one's new.  You will need to provide all three
 		function callbacks, even if you aren't using them all.
-		You can put a void pointer in place of the NULL, and
+		You can use any void pointer as the user_ptr, and
 		retrieve the pointer from inside the callbacks using
       the function png_get_progressive_ptr(png_ptr); */
-	png_set_progressive_read_fn(png_ptr, NULL,
+	png_set_progressive_read_fn(png_ptr, user_ptr,
 		info_callback, row_callback, end_callback);
 
 	return 0;
@@ -597,11 +633,11 @@ end_callback(png_structp png_ptr, png_infop info)
 }
 
 
-Writing PNG files:
+IV. Writing
 
 Much of this is very similar to reading.  However, everything of
 importance is repeated here, so you don't have to constantly look
-back up in the Reading PNG files section to understand writing.
+back up in the reading section to understand writing.
 
 The first thing you need to do while writing a PNG file is to allocate
 and initialize png_struct and png_info.  As these are both large, you
@@ -638,8 +674,8 @@ write the file from different routines, you will need to update
 the jmpbuf field every time you enter a new routine that will
 call a png_ function.  See your documentation of setjmp/longjmp
 for your compiler for more information on setjmp/longjmp.  See
-the discussion on png error handling in the Customizing Libpng
+the discussion on libpng error handling in the Customizing Libpng
-section below for more information on the png error handling.
+section below for more information on the libpng error handling.
 
    if (setjmp(png_ptr->jmpbuf))
    {
@@ -652,7 +688,7 @@ section below for more information on the png error handling.
       return;
    }
 
-Next, you will need to call png_write_init() and png_info_init().
+Next, you will need to call png_info_init() and png_write_init().
 These functions make sure all the fields are initialized to useful
 values, and, in the case of png_write_init(), allocate any memory
 needed for internal uses.  Do png_info_init() first, so if
@@ -684,6 +720,7 @@ See the compression library for more details.
    /* turn on or off filtering (1 or 0) */
    png_set_filtering(png_ptr, 1);
 
+   /* compression level (0 - none, 6 - default, 9 - maximum) */
 	png_set_compression_level(png_ptr, Z_DEFAULT_COMPRESSION);
    png_set_compression_mem_level(png_ptr, 8);
    png_set_compression_strategy(png_ptr, Z_DEFAULT_STRATEGY);
@@ -696,9 +733,11 @@ you are allowed to write after the image is the text chunks and the
 time chunk.  See png_write_end() for more information on that.  If you
 wish to write them before the image, fill them in now.  If you want to
 wait until after the data, don't fill them until png_write_end().  For
-all the fields in png_info, see png.h.  For explinations of what the
+all the fields in png_info, see png.h.  For explanations of what the
-fields contain, see the PNG specification.  Some of the more important
+fields contain, see the PNG specification.
-parts of the png_info are:
+
+Some of the more important parts of the png_info are:
+
 	width          - holds the width of the file
 	height         - holds the height of the file
 	bit_depth      - holds the bit depth of one of the image channels
@@ -706,16 +745,24 @@ parts of the png_info are:
 						  see the PNG_COLOR_TYPE_ defines for more information
    interlace_type - currently 0 for none, 1 for interlaced
 	valid          - this describes which optional chunks to write to the
-      file.  Note that if you are writing a PNG_COLOR_TYPE_PALETTE
+						  file.  Note that if you are writing a
-      file, the PLTE chunk is not optional, but must still be marked
+						  PNG_COLOR_TYPE_PALETTE file, the PLTE chunk is not
-      for writing.  To mark chunks for writing, OR valid with the
+						  optional, but must still be marked for writing.  To
-      appropriate PNG_INFO_<chunk name> define.
+						  mark chunks for writing, OR valid with the appropriate
-   palette and num_palette - the palette for the file
+						  PNG_INFO_<chunk name> define.
+	palette        - the palette for the file
+	num_palette    - number of entries in the palette
 	gamma          - the gamma the file is written at
-   sig_bit and sig_bit_number - the number of significant bits
+	sig_bit        - the number of significant bits
-   trans, trans_values, and number_trans - transparency info
+						  for the gray, red, green, and blue channels, whichever are
+						  appropriate for the given color type.
+   sig_bit_number - number of channels
+	trans_values   - transparent pixel for non-paletted images
+	trans          - array of transparent entries for paletted images
+	number_trans   - number of transparent entries
 	hist           - histogram of palette
-   text and num_text - text comments in the file.
+	text           - text comments in the file.
+	num_text       - number of comments
 
 A quick word about text and num_text.  text is an array of png_text
 structures.  num_text is the number of valid structures in the array.
@@ -751,7 +798,29 @@ time_t and png_convert_from_struct_tm() for struct tm.  The
 time_t routine uses gmtime().  You don't have to use either of
 these, but if you wish to fill in the png_time structure directly,
 you should provide the time in universal time (GMT) if possible
-instead of your local time.
+instead of your local time.  Note that the year number is the full
+year (ie 1996, rather than 96)
+
+It is possible to have libpng flush any pending output, either manually,
+or automatically after a certain number of lines have been written.  To
+flush the output stream a single time call:
+
+	png_write_flush(png_ptr);
+
+and to have libpng flush the output stream periodically after a certain
+number of scanlines have been written, call:
+
+	png_set_flush(png_ptr, nrows);
+
+Note that the distance between rows is from the last time png_write_flush
+was called, or the first row of the image if it has never been called.
+So if you write 50 lines, and then png_set_flush 25, it will flush the
+output on the next scanline, and on line 75, unless png_write_flush is
+called earlier.  If nrows is too small (less than about 10 lines) the
+image compression may decrease dramatically (although this may be
+acceptable for real-time applications).  Infrequent flushing will only
+degrade the compression performance by a few percent over images that
+do not use flushing.
 
 You are now ready to write all the file information up to the actual
 image data.  You do this with a call to png_write_info().
@@ -768,8 +837,8 @@ check to see if it has data that it can do somthing with, you should
 make sure to only enable a transformation if it will be valid for
 the data.  For example, don't swap red and blue on grayscale data.
 
-PNG files store rgb pixels packed into 3 bytes.  If you would rather
+PNG files store rgb pixels packed into 3 bytes.  This code tells
-supply the pixels as 4 bytes per pixel, call this:
+the library to use 4 bytes per pixel
 
 	png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
 
@@ -779,8 +848,8 @@ want the filler before the rgb or after.
 
 PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
 they can, resulting in, for example, 8 pixels per byte for 1 bit files.
-If you would rather supply the data 1 pixel per byte, but with the
+If the data is supplied at 1 pixel per byte, use this code, which will
-values limited to the correct number of bits, call this:
+correctly pack the values:
 
 	png_set_packing(png_ptr);
 
@@ -813,20 +882,21 @@ they want, can reduce the values down to their true depth.
 
    png_set_shift(png_ptr, &(info_ptr->sig_bit));
 
-PNG files store 16 bit pixels in network byte order (most significant
+PNG files store 16 bit pixels in network byte order (big-endian,
-bit first).  If you would rather supply them the other way, (the way
+ie. most significant bits first).  This code would be used to supply
-PC's store them, for example), call this:
+them the other way (little-endian, ie. least significant bits first,
+eg. the way PCs store them):
 
    png_set_swap(png_ptr);
 
-PNG files store 3 color pixels in red, green, blue order.  If you would
+PNG files store 3 color pixels in red, green, blue order.  This code
-rather supply the pixels as blue, green, red, call this.
+would be used to supply the pixels as blue, green, red:
 
    png_set_bgr(png_ptr);
 
-PNG files describe moncrome as black is zero and white is one.  If you
+PNG files describe monochrome as black being zero and white being
-would rather supply the pixels with this reversed (black is one and
+one. This code would be used to supply the pixels with this reversed
-white is zero), call this:
+(black being one and white being zero):
 
 	png_set_invert(png_ptr);
 
@@ -861,18 +931,20 @@ row_pointers:
 
    png_write_rows(png_ptr, &row_pointers, 1);
 
-When the file is interlaced, things can get a good deal harder.
+When the file is interlaced, things can get a good deal more
-PNG files have a complicated interlace scheme that breaks down an
+complicated.  The only currently (as of 12/95) defined interlacing
-image into seven smaller images of varying size.  Libpng will
+scheme for PNG files is a compilcated interlace scheme, known as
-build these images if you want, or you can do them yourself.  If
+Adam7, that breaks down an image into seven smaller images of varying
-you want to build them yourself, see the PNG specification for
+size.  libpng will build these images for you, or you can do them
-details of which pixels to write when.
+yourself.  If you want to build them yourself, see the PNG
+specification for details of which pixels to write when.
 
 If you don't want libpng to handle the interlacing details, just
 call png_write_rows() the correct number of times to write all
 seven sub-images.
 
-If you want libpng to build the sub-images, call this:
+If you want libpng to build the sub-images, call this before you start
+writing any rows:
 
 	number_passes = png_set_interlace_handling(png_ptr);
 
@@ -906,7 +978,7 @@ read or write.  For a more compact example of writing a PNG image,
 see the file example.c.
 
 
-Customizing libpng:
+V. Modifying/Customizing libpng:
 
 There are two issues here.  The first is changing how libpng does
 standard things like memory allocation, input/output, and error handling.
@@ -916,21 +988,24 @@ adding new transformations, and generally changing how libpng works.
 All of the memory allocation, input/output, and error handling in libpng
 goes through callbacks which are user setable.  The default routines
 are in pngerror.c, pngmem.c, and pngio.c.  To change these functions,
-call the approprate fn function.
+call the approprate _fn function.
 
 Memory allocation is done through the functions png_large_malloc(),
 png_malloc(), png_realloc(), png_large_free(), and png_free().
 These currently just call the standard C functions.  The large
 functions must handle exactly 64K, but they don't have to handle
 more then that.  If your pointers can't access more then 64K at a
-time, you will want to set MAXSEG_64K in zlib.h.
+time, you will want to set MAXSEG_64K in zlib.h.  Since it is unlikely
+that the method of handling memory allocation on a platform will
+change between applications, these functions must be modified in the
+library at compile time.
 
 Input/Output in libpng is done throught png_read() and png_write(), which
 currently just call fread() and fwrite().  The FILE * is stored in
 png_struct, and is initialized via png_init_io().  If you wish to change
-this, the library supplies callbacks that you can set through the
+the method of I/O, the library supplies callbacks that you can set through
-function png_set_read_fn() and png_set_write_fn().  These functions
+the function png_set_read_fn() and png_set_write_fn() at run time.  These
-also provide a void pointer that can be retrieved via the function
+functions also provide a void pointer that can be retrieved via the function
 png_get_io_ptr().  For example:
 
 	png_set_read_fn(png_structp png_ptr, voidp io_ptr,
@@ -941,30 +1016,45 @@ png_get_io_ptr().  For example:
 
 	voidp io_ptr = png_get_io_ptr(png_ptr);
 
+The replacement I/O functions should have prototypes as follows:
+
+	void user_read_data(png_structp png_ptr, png_bytep data,
+		png_uint_32 length);
+	void user_write_data(png_structp png_ptr, png_bytep data,
+		png_uint_32 length);
+	void user_flush_data(png_structp png_ptr);
+
 Note that you can pass NULL for the flush function if you are not doing
-flushing.
+flushing of the output data.
 
 Error handling in libpng is done through png_error() and png_warning().
 Errors handled through png_error() are fatal, meaning that png_error()
 should never return to it's caller.  Currently, this is handled via
 setjmp() and longjmp(), but you could change this to do things like
-exit() if you should wish.  Similarly, both png_error() and png_warning()
+exit() if you should wish.  On non-fatal errors, png_warning() is called
-print a message on stderr, but that can also be changed.  The motivation
+to print a warning message, and then control returns to the calling code.
-behind using setjmp() and longjmp() is the C++ throw and catch exception
+By default png_error() and png_warning() print a message on stderr.  If
-handling methods.  This makes the code much easier to write, as there
+you wish to change the behavior of the error functions, you will need to
-is no need to check every return code of every function call.  However,
+set up your own message callbacks.  You do this like the I/O callbacks above.
-there are some uncertainties about the status of local variables after
-a longjmp, so the user may want to be careful about doing anything after
-setjmp returns non zero besides returning itself.  Consult your compiler
-documentation for more details.  If you wish to change this behavior,
-you will need to set up your own message callbacks.  You do this like
-the io callbacks above.
 
 	  png_set_message_fn(png_structp png_ptr, png_voidp msg_ptr,
 		  png_msg_ptr error_fn, png_msg_ptr warning_fn);
 
 	  png_voidp msg_ptr = png_get_msg_ptr(png_ptr);
 
+The replacement message functions should have parameters as follows:
+
+	void user_error_fn(png_struct png_ptr, png_const_charp error_msg);
+	void user_warning_fn(png_struct png_ptr, png_const_charp warning_msg);
+
+The motivation behind using setjmp() and longjmp() is the C++ throw and
+catch exception handling methods.  This makes the code much easier to write,
+as there is no need to check every return code of every function call.
+However, there are some uncertainties about the status of local variables
+after a longjmp, so the user may want to be careful about doing anything after
+setjmp returns non zero besides returning itself.  Consult your compiler
+documentation for more details.
+
 If you need to read or write custom chunks, you will need to get deeper
 into the libpng code.  First, read the PNG specification, and have
 a first level of understanding of how it works.  Pay particular
@@ -983,7 +1073,7 @@ itself.
 
 Configuring for 16 bit platforms:
 
-You will may need to change the png_large_malloc() and
+You will probably need to change the png_large_malloc() and
 png_large_free() routines in pngmem.c, as these are requred
 to allocate 64K.  Also, you will want to look into zconf.h to tell
 zlib (and thus libpng) that it cannot allocate more then 64K at a
@@ -993,8 +1083,8 @@ and libpng to 64K by defining MAXSEG_64K.
 Configuring for Medium Model:
 
 Libpng's support for medium model has been tested on most of the popular
-complers.  Make sure MAXSEG_64K get's defined, USE_FAR_KEYWORD get's
+complers.  Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
-defined, and FAR get's defined to far in pngconf.h, and you should be
+defined, and FAR gets defined to far in pngconf.h, and you should be
 all set.  Everything in the library (except for zlib's structure) is
 expecting far data.  You must use the typedefs with the p or pp on
 the end for pointers (or at least look at them and be careful).  Make
@@ -1012,7 +1102,7 @@ memory allocators (png_malloc, etc.).
 
 Configuring for compiler xxx:
 
-All includes for libpng are in png.h.  If you need to add/change/delete
+All includes for libpng are in pngconf.h.  If you need to add/change/delete
 an include, this is the place to do it.  The includes that are not
 needed outside libpng are protected by the PNG_INTERNAL definition,
 which is only defined for those routines inside libpng itself.  The
@@ -1020,9 +1110,9 @@ files in libpng proper only include png.h.
 
 Removing unwanted object code:
 
-There are a bunch of #define's in png.h that control what parts of
+There are a bunch of #define's in pngconf.h that control what parts of
 libpng are compiled.  All the defines end in _SUPPORT.  If you are
-not using an ability, you can change the #define to #undef and
+never going to use an ability, you can change the #define to #undef and
 save yourself code and data space.  All the reading and writing
 specific code are in seperate files, so the linker should only grab
 the files it needs.  However, if you want to make sure, or if you

png.c

@@ -1,10 +1,10 @@
 
 /* png.c - location for general purpose png functions
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
    */
 
 #define PNG_INTERNAL
@@ -13,7 +13,7 @@
 
 /* version information for c files.  This better match the version
    string defined in png.h */
-char FARDATA png_libpng_ver[] = "0.85";
+char FARDATA png_libpng_ver[] = "0.86";
 
 /* place to hold the signiture string for a png file. */
 png_byte FARDATA png_sig[8] = {137, 80, 78, 71, 13, 10, 26, 10};
@@ -107,7 +107,7 @@ png_check_sig(png_bytep sig, int num)
 voidpf
 png_zalloc(voidpf png_ptr, uInt items, uInt size)
 {
-	voidp * ptr;
+	voidp ptr;
 
 	ptr = ((voidp)png_large_malloc((png_structp)png_ptr,
 		(png_uint_32)items * (png_uint_32)size));

png.h

@@ -1,8 +1,8 @@
 
 /* png.h - header file for png reference library
 
-   libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
-   December 19, 1995
+	Jan 10, 1996
 
 	Note: This is a beta version.  It reads and writes valid files
 	on the platforms I have, but it has had limited portability
@@ -15,13 +15,20 @@
 
 	See readme.txt for more information
 
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+   Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
 	Contributing Authors:
+      Andreas Dilger
       Dave Martindale
 		Guy Eric Schalnat
 		Paul Schmidt
 		Tim Wegner
 
+	The contributing authors would like to thank all those who helped
+	with testing, bug fixes, and patience.  You know who you are.  This
+	wouldn't have been possible without all of you.
+
+   Thanks to Frank J. T. Wojcik for reviewing the documentation
+
    The PNG Reference Library is supplied "AS IS". The Contributing Authors
    and Group 42, Inc. disclaim all warranties, expressed or implied,
    including, without limitation, the warranties of merchantability and of
@@ -67,10 +74,10 @@
 
 /* version information for png.h - this should match the version
    number in png.c */
-#define PNG_LIBPNG_VER_STRING "0.85"
+#define PNG_LIBPNG_VER_STRING "0.86"
-/* careful here.  I wanted to use 085, but that would be octal.  Version
+/* careful here.  I wanted to use 086, but that would be octal.  Version
 	1.0 will be 100 here, etc. */
-#define PNG_LIBPNG_VER 85
+#define PNG_LIBPNG_VER 86
 
 /* variables defined in png.c - only it needs to define PNG_NO_EXTERN */
 #ifndef PNG_NO_EXTERN
@@ -265,6 +272,7 @@ typedef png_info        FAR * FAR * png_infopp;
 /* these determine if a function in the info needs freed */
 #define PNG_FREE_PALETTE 0x0001
 #define PNG_FREE_HIST 0x0002
+#define PNG_FREE_TRANS 0x0004
 
 /* this is used for the transformation routines, as some of them
 	change these values for the row.  It also should enable using
@@ -290,10 +298,10 @@ typedef png_row_info    FAR * FAR * png_row_infopp;
 typedef struct png_struct_def png_struct;
 typedef png_struct FAR * png_structp;
 
-#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
 typedef void (*png_msg_ptr) PNGARG((png_structp, png_const_charp));
 typedef void (*png_rw_ptr) PNGARG((png_structp, png_bytep, png_uint_32));
 typedef void (*png_flush_ptr) PNGARG((png_structp));
+#ifdef PNG_PROGRESSIVE_READ_SUPPORTED
 typedef void (*png_progressive_info_ptr) PNGARG((png_structp, png_infop));
 typedef void (*png_progressive_end_ptr) PNGARG((png_structp, png_infop));
 typedef void (*png_progressive_row_ptr) PNGARG((png_structp, png_bytep,
@@ -305,7 +313,7 @@ typedef void (*png_progressive_row_ptr) PNGARG((png_structp, png_bytep,
 	people who will be modifying the library for their own special needs.
 	*/
 
-typedef struct png_struct_def
+struct png_struct_def
 {
 	jmp_buf jmpbuf; /* used in png_error */
 	png_byte mode; /* used to determine where we are in the png file */
@@ -507,6 +515,11 @@ extern void png_set_expand PNGARG((png_structp png_ptr));
 extern void png_set_bgr PNGARG((png_structp png_ptr));
 #endif
 
+#if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
+/* Expand the grayscale to 24 bit RGB if necessary. */
+extern void png_set_gray_to_rgb PNGARG((png_structp png_ptr));
+#endif
+
 #if defined(PNG_READ_FILLER_SUPPORTED) || defined(PNG_WRITE_FILLER_SUPPORTED)
 #define PNG_FILLER_BEFORE 0
 #define PNG_FILLER_AFTER 1
@@ -664,9 +677,10 @@ extern void png_set_compression_method PNGARG((png_structp png_ptr,
    int method));
 
 /* These next functions are stubs of typical c functions for input/output,
-   memory, and error handling.  They are in the file pngstub.c, and are
+	memory, and error handling.  They are in the file pngio.c, and pngerror.c.
-   set up to be easily modified for users that need to.  See the file
+	These functions can be replaced at run time for those applications that
-   pngstub.c for more information */
+	need to handle I/O in a different manner.  See the file libpng.txt for
+	more information */
 
 /* Write the data to whatever output you are using. */
 extern void png_write_data PNGARG((png_structp png_ptr, png_bytep data,
@@ -676,7 +690,7 @@ extern void png_write_data PNGARG((png_structp png_ptr, png_bytep data,
 extern void png_read_data PNGARG((png_structp png_ptr, png_bytep data,
 	png_uint_32 length));
 
-/* Initialize the input/output for the png file. */
+/* Initialize the input/output for the png file to the default functions. */
 extern void png_init_io PNGARG((png_structp png_ptr, FILE *fp));
 
 /* Replace the error message and abort, and warning functions with user
@@ -691,7 +705,7 @@ extern png_voidp png_get_msg_ptr PNGARG((png_structp png_ptr));
 
 /* Replace the default data output functions with a user supplied one(s).
 	If buffered output is not used, then output_flush_fn can be set to NULL.
-	if PNG_WRITE_FLUSH_SUPPORTED is not defined at libpng compile time
+	If PNG_WRITE_FLUSH_SUPPORTED is not defined at libpng compile time
 	output_flush_fn will be ignored (and thus can be NULL). */
 extern void png_set_write_fn PNGARG((png_structp png_ptr, png_voidp io_ptr,
 	png_rw_ptr write_data_fn, png_flush_ptr output_flush_fn));
@@ -709,7 +723,7 @@ extern void png_set_push_fn PNGARG((png_structp png_ptr, png_voidp push_ptr,
 	png_progressive_end_ptr end_fn));
 
 /* returns the user pointer assiciated with the push read functions */
-extern void * png_get_progressive_ptr PNGARG((png_structp png_ptr));
+extern png_voidp png_get_progressive_ptr PNGARG((png_structp png_ptr));
 
 extern png_voidp png_large_malloc PNGARG((png_structp png_ptr,
 	png_uint_32 size));
@@ -1118,6 +1132,9 @@ extern void png_do_unshift PNGARG((png_row_infop row_info, png_bytep row,
 extern void png_do_invert PNGARG((png_row_infop row_info, png_bytep row));
 #endif
 
+extern void png_build_grayscale_palette PNGARG((int bit_depth,
+	png_colorp palette));
+
 #if defined(PNG_READ_GRAY_TO_RGB_SUPPORTED)
 extern void png_do_gray_to_rgb PNGARG((png_row_infop row_info,
 	png_bytep row));

pngchang.txt

@@ -62,5 +62,8 @@ version 0.85
    added i/o, error, and memory callback functions
    fixed some bugs (16 bit, 4 bit interlaced, etc.)
    added first run progressive reader (barely tested)
+version 0.86
+   fixed bugs
+   improved documentation
 
 

pngconf.h

@@ -1,10 +1,10 @@
 
 /* pngconf.c - machine configurable file for libpng
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
    */
 
 /* Any machine specific code is near the front of this file, so if you

pngerror.c

@@ -1,21 +1,23 @@
 
 /* pngerror.c - stub functions for i/o and memory allocation
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
 
 	This file provides a location for all error handling.  Users which
-   need special error handling are expected to modify the code in this
+   need special error handling are expected to write replacement functions
-   file to meet their needs.  See the instructions at each function. */
+	and use png_set_message_fn() to use those functions.  See the instructions
+	at each function. */
 
 #define PNG_INTERNAL
 #include "png.h"
 
-/* This function is called whenever there is an error.  Replace with
+/* This function is called whenever there is a fatal error.  This function
-	however you wish to handle the error.  Note that this function
+	should not be changed.  If there is a need to handle errors differently,
-	MUST NOT return, or the program will crash */
+	you should supply a replacement error function and use png_set_message_fn()
+   to replace the error function at run-time. */
 void
 png_error(png_structp png_ptr, png_const_charp message)
 {
@@ -27,6 +29,10 @@ png_error(png_structp png_ptr, png_const_charp message)
 	png_default_error(png_ptr, message);
 }
 
+/* This function is called whenever there is a non-fatal error.  This function
+	should not be changed.  If there is a need to handle warnings differently,
+	you should supply a replacement warning function and use
+	png_set_message_fn() to replace the warning function at run-time. */
 void
 png_warning(png_structp png_ptr, png_const_charp message)
 {
@@ -54,11 +60,10 @@ png_default_error(png_structp png_ptr, png_const_charp message)
 #endif
 }
 
-/* This function is called when there is a warning, but the library
+/* This function is called when there is a warning, but the library thinks
-   thinks it can continue anyway.  You don't have to do anything here
+	it can continue anyway.  Replacement functions don't have to do anything
-   if you don't want to.  In the default configuration, png_ptr is
+	here if you don't want to.  In the default configuration, png_ptr is
    not used, but it is passed in case it may be useful. */
-
 void
 png_default_warning(png_structp png_ptr, png_const_charp message)
 {
@@ -70,10 +75,10 @@ png_default_warning(png_structp png_ptr, png_const_charp message)
 #endif
 }
 
-/* This function is called when the application wants to use another
+/* This function is called when the application wants to use another method
-	method of handling errors and warnings.  Note that the error function must
+	of handling errors and warnings.  Note that the error function MUST NOT
-	NOT return to the calling routine or serious problems will occur. The
+	return to the calling routine or serious problems will occur. The error
-	error return method used in the default routine calls
+	return method used in the default routine calls
 	longjmp(png_ptr->jmpbuf, 1) */
 void
 png_set_message_fn(png_structp png_ptr, png_voidp msg_ptr, png_msg_ptr error_fn,

pngio.c

@@ -1,10 +1,10 @@
 
-/* pngstub.c - stub functions for i/o and memory allocation
+/* pngio.c - stub functions for i/o and memory allocation
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
 
    This file provides a location for all input/output.  Users which need
 	special handling are expected to write functions which have the same
@@ -16,13 +16,12 @@
 #define PNG_INTERNAL
 #include "png.h"
 
-/* Write the data to whatever output you are using.  The default
+/* Write the data to whatever output you are using.  The default routine
-   routine writes to a file pointer.  If you need to write to something
+	writes to a file pointer.  Note that this routine sometimes gets called
-	else, this is a good example of how to do it.  Note that this routine
+	with very small lengths, so you should implement some kind of simple
-	sometimes gets called with very small lengths, so you should implement
+	buffering if you are using unbuffered writes.  This should never be asked
-	some kind of simple buffering if you are using unbuffered writes.  This
+	to write more then 64K on a 16 bit machine.  The cast to png_size_t is
-	should never be asked to write more then 64K on a 16 bit machine.  The
+	there to quiet warnings of certain compilers. */
-	cast to png_size_t is there for insurance. */
 
 void
 png_write_data(png_structp png_ptr, png_bytep data, png_uint_32 length)
@@ -33,6 +32,10 @@ png_write_data(png_structp png_ptr, png_bytep data, png_uint_32 length)
 		png_error(png_ptr, "Call to NULL write function");
 }
 
+/* This is the function which does the actual writing of data.  If you are
+	not writing to a standard C stream, you should create a replacement
+	write_data function and use it at run time with png_set_write_fn(), rather
+	than changing the library. */
 #ifndef USE_FAR_KEYWORD
 void
 png_default_write_data(png_structp png_ptr, png_bytep data, png_uint_32 length)
@@ -106,17 +109,12 @@ png_default_write_data(png_structp png_ptr, png_bytep data, png_uint_32 length)
 
 #endif
 
-/* Read the data from whatever input you are using.  The default
+/* Read the data from whatever input you are using.  The default routine
-   routine reads from a file pointer.  If you need to read from something
+	reads from a file pointer.  Note that this routine sometimes gets called
-   else, this is the place to do it.  We suggest saving the old code
+	with very small lengths, so you should implement some kind of simple
-   for future use.  Note that this routine sometimes gets called with
+	buffering if you are using unbuffered reads.  This should never be asked
-   very small lengths, so you should implement some kind of simple
+	to read more then 64K on a 16 bit machine.  The cast to png_size_t is
-   buffering if you are using unbuffered reads.  This should
+	there to quiet some compilers */
-   never be asked to read more then 64K on a 16 bit machine.  The cast
-	to png_size_t is there for insurance, but if you are having problems
-	with it, you can take it out.  Just be sure to cast length to whatever
-	fread needs in that spot if you don't have a function prototype for
-	it. */
 void
 png_read_data(png_structp png_ptr, png_bytep data, png_uint_32 length)
 {
@@ -135,6 +133,10 @@ png_read_data(png_structp png_ptr, png_bytep data, png_uint_32 length)
 	}
 }
 
+/* This is the function which does the actual reading of data.  If you are
+	not reading from a standard C stream, you should create a replacement
+	read_data function and use it at run time with png_set_read_fn(), rather
+	than changing the library. */
 #ifndef USE_FAR_KEYWORD
 void
 png_default_read_data(png_structp png_ptr, png_bytep data, png_uint_32 length)
@@ -221,7 +223,7 @@ png_default_flush(png_struct *png_ptr)
 						 arguments a pointer to a png_struct, a pointer to
 						 data to be written, and a 32-bit unsigned int which is
 						 the number of bytes to be written.  The new write
-						 function should call (*(png_ptr->error_fn))("Error msg")
+						 function should call png_error("Error msg")
 						 to exit and output any fatal error messages.
 	flush_data_fn - pointer to a new flush function which takes as its
 						 arguments a pointer to a png_struct.  After a call to
@@ -264,7 +266,9 @@ png_set_write_fn(png_structp png_ptr, png_voidp io_ptr, png_rw_ptr write_data_fn
 	read_data_fn - pointer to a new input function which takes as it's
 						arguments a pointer to a png_struct, a pointer to
 						a location where input data can be stored, and a 32-bit
-						unsigned int which is the number of bytes to be read. */
+						unsigned int which is the number of bytes to be read.
+						To exit and output any fatal error messages the new write
+                  function should call png_error(png_ptr, "Error msg"). */
 void
 png_set_read_fn(png_struct *png_ptr, void *io_ptr, png_rw_ptr read_data_fn)
 {
@@ -293,10 +297,9 @@ png_get_io_ptr(png_struct *png_ptr)
 	return png_ptr->io_ptr;
 }
 
-/* Initialize the input/output for the png file.  If you change
+/* Initialize the default input/output functions for the png file.  If you
-	the read and write routines, you will probably need to change
+	change the read, or write routines, you can call either png_set_read_fn()
-   this routine (or write your own).  If you change the parameters
+   or png_set_write_fn() instead of png_init_io(). */
-   of this routine, remember to change png.h also. */
 void
 png_init_io(png_structp png_ptr, FILE *fp)
 {

pngmem.c

@@ -1,10 +1,10 @@
 
 /* pngmem.c - stub functions for memory allocation
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
 
    This file provides a location for all memory allocation.  Users which
 	need special memory handling are expected to modify the code in this file

pngpread.c

@@ -1,10 +1,10 @@
 
 /* pngpread.c - read a png file in push mode
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
    */
 
 #define PNG_INTERNAL
@@ -850,8 +850,10 @@ png_push_read_text(png_structp png_ptr, png_infop info)
 			text_size = png_ptr->buffer_size;
 		else
 			text_size = png_ptr->current_text_left;
-		png_push_fill_buffer(png_ptr, png_ptr->current_text_ptr, text_size);
+		png_push_fill_buffer(png_ptr, (png_bytep)png_ptr->current_text_ptr,
-		png_calculate_crc(png_ptr, png_ptr->current_text_ptr, text_size);
+			text_size);
+		png_calculate_crc(png_ptr, (png_bytep)png_ptr->current_text_ptr,
+			text_size);
 		png_ptr->current_text_left -= text_size;
 		png_ptr->current_text_ptr += text_size;
 	}
@@ -902,8 +904,10 @@ png_push_read_ztxt(png_structp png_ptr, png_infop info)
 			text_size = png_ptr->buffer_size;
 		else
 			text_size = png_ptr->current_text_left;
-		png_push_fill_buffer(png_ptr, png_ptr->current_text_ptr, text_size);
+		png_push_fill_buffer(png_ptr, (png_bytep)png_ptr->current_text_ptr,
-		png_calculate_crc(png_ptr, png_ptr->current_text_ptr, text_size);
+			text_size);
+		png_calculate_crc(png_ptr, (png_bytep)png_ptr->current_text_ptr,
+			text_size);
 		png_ptr->current_text_left -= text_size;
 		png_ptr->current_text_ptr += text_size;
 	}
@@ -950,6 +954,7 @@ png_push_read_ztxt(png_structp png_ptr, png_infop info)
 		key_size = text - key;
 		text_size = 0;
 		text = NULL;
+      ret = Z_STREAM_END;
 
 		while (png_ptr->zstream->avail_in)
 		{

pngrcb.c

@@ -1,9 +1,9 @@
 /* pngrcb.c - callbacks while reading a png file
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
    */
 
 #define PNG_INTERNAL

pngread.c

@@ -1,10 +1,10 @@
 
 /* pngread.c - read a png file
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
    */
 
 #define PNG_INTERNAL
@@ -633,7 +633,7 @@ png_read_destroy(png_structp png_ptr, png_infop info, png_infop end_info)
 		if (png_ptr->do_free & PNG_FREE_PALETTE)
 			png_free(png_ptr, info->palette);
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) && defined(PNG_READ_bKGD_SUPPORTED)
-		if (png_ptr->do_free & PNG_FREE_PALETTE)
+		if (png_ptr->do_free & PNG_FREE_TRANS)
 			png_free(png_ptr, info->trans);
 #endif
 #if defined(PNG_READ_hIST_SUPPORTED)

pngrtran.c

@@ -1,10 +1,10 @@
 
 /* pngrtran.c - transforms the data in a row for png readers
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
    */
 
 #define PNG_INTERNAL
@@ -1169,6 +1169,7 @@ png_build_grayscale_palette(int bit_depth, png_colorp palette)
          break;
       default:
 			num_palette = 0;
+         color_inc = 0;
          break;
    }
 
@@ -2025,7 +2026,7 @@ png_do_background(png_row_infop row_info, png_bytep row,
    you do this after you deal with the trasparency issue on grayscale
    or rgb images. If your bit depth is 8, use gamma_table, if it is 16,
    use gamma_16_table and gamma_shift.  Build these with
-   build_gamma_table().  If your bit depth < 8, gamma correct a
+   build_gamma_table().  If your bit depth <= 8, gamma correct a
    palette, not the data.  */
 void
 png_do_gamma(png_row_infop row_info, png_bytep row,
@@ -2709,10 +2710,10 @@ png_build_gamma_table(png_structp png_ptr)
 			{
 				fout = ((double)i + 0.5) / 256.0;
 				fin = pow(fout, g);
-				max = (png_uint_32)(fin * (double)(num << 8));
+				max = (png_uint_32)(fin * (double)((png_uint_32)num << 8));
 				while (last <= max)
 				{
-					png_ptr->gamma_16_table[(int)(last & 0xff) >> shift]
+					png_ptr->gamma_16_table[(int)(last & (0xff >> shift))]
 						[(int)(last >> (8 - shift))] =
 						(png_uint_16)i | ((png_uint_16)i << 8);
 					last++;
@@ -2720,7 +2721,7 @@ png_build_gamma_table(png_structp png_ptr)
 			}
 			while (last < ((png_uint_32)num << 8))
 			{
-					png_ptr->gamma_16_table[(int)(last & 0xff) >> shift]
+				png_ptr->gamma_16_table[(int)(last & (0xff >> shift))]
 					[(int)(last >> (8 - shift))] =
 					(png_uint_16)65535L;
 				last++;

pngrutil.c

@@ -1,10 +1,10 @@
 
 /* pngrutil.c - utilities to read a png file
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
    */
 
 #define PNG_INTERNAL
@@ -164,6 +164,7 @@ png_handle_PLTE(png_structp png_ptr, png_infop info, png_uint_32 length)
 
    num = (int)length / 3;
    palette = (png_colorp)png_malloc(png_ptr, num * sizeof (png_color));
+   png_ptr->do_free |= PNG_FREE_PALETTE;
 	for (i = 0; i < num; i++)
    {
       png_byte buf[3];
@@ -189,6 +190,7 @@ png_handle_gAMA(png_structp png_ptr, png_infop info, png_uint_32 length)
 
    if (length != 4)
    {
+      png_warning(png_ptr, "Incorrect gAMA chunk length");
 		png_crc_skip(png_ptr, length);
       return;
    }
@@ -212,6 +214,8 @@ png_handle_sBIT(png_structp png_ptr, png_infop info, png_uint_32 length)
    int slen;
 	png_byte buf[4];
 
+   buf[0] = buf[1] = buf[2] = buf[3] = 0;
+
    if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
       slen = 3;
    else
@@ -219,6 +223,7 @@ png_handle_sBIT(png_structp png_ptr, png_infop info, png_uint_32 length)
 
    if (length != (png_uint_32)slen)
    {
+      png_warning(png_ptr, "Incorrect sBIT chunk length");
 		png_crc_skip(png_ptr, length);
 		return;
    }
@@ -250,6 +255,7 @@ png_handle_cHRM(png_structp png_ptr, png_infop info, png_uint_32 length)
 
    if (length != 32)
    {
+      png_warning(png_ptr, "Incorrect cHRM chunk length");
 		png_crc_skip(png_ptr, length);
 		return;
    }
@@ -299,11 +305,13 @@ png_handle_tRNS(png_structp png_ptr, png_infop info, png_uint_32 length)
    {
       if (length > png_ptr->num_palette)
       {
+         png_warning(png_ptr, "Incorrect tRNS chunk length");
 			png_crc_skip(png_ptr, length);
          return;
       }
 
       png_ptr->trans = (png_bytep)png_malloc(png_ptr, length);
+      png_ptr->do_free |= PNG_FREE_TRANS;
 		png_crc_read(png_ptr, png_ptr->trans, length);
 		png_ptr->num_trans = (int)length;
    }
@@ -313,6 +321,7 @@ png_handle_tRNS(png_structp png_ptr, png_infop info, png_uint_32 length)
 
       if (length != 6)
       {
+         png_warning(png_ptr, "Incorrect tRNS chunk length");
 			png_crc_skip(png_ptr, length);
          return;
       }
@@ -329,6 +338,7 @@ png_handle_tRNS(png_structp png_ptr, png_infop info, png_uint_32 length)
 
       if (length != 2)
       {
+         png_warning(png_ptr, "Incorrect tRNS chunk length");
 			png_crc_skip(png_ptr, length);
 			return;
 		}
@@ -338,7 +348,7 @@ png_handle_tRNS(png_structp png_ptr, png_infop info, png_uint_32 length)
 		png_ptr->trans_values.gray = png_get_uint_16(buf);
 	}
 	else
-      png_error(png_ptr, "Invalid tRNS chunk");
+      png_warning(png_ptr, "Invalid tRNS chunk");
 
    png_read_tRNS(png_ptr, info, png_ptr->trans, png_ptr->num_trans,
       &(png_ptr->trans_values));
@@ -361,6 +371,7 @@ png_handle_bKGD(png_structp png_ptr, png_infop info, png_uint_32 length)
 
    if (length != (png_uint_32)truelen)
    {
+		png_warning(png_ptr, "Incorrect bKGD chunk length");
 		png_crc_skip(png_ptr, length);
       return;
    }
@@ -389,6 +400,7 @@ png_handle_hIST(png_structp png_ptr, png_infop info, png_uint_32 length)
 
 	if (length != 2 * png_ptr->num_palette)
 	{
+		png_warning(png_ptr, "Incorrect hIST chunk length");
 		png_crc_skip(png_ptr, length);
 		return;
 	}
@@ -396,6 +408,7 @@ png_handle_hIST(png_structp png_ptr, png_infop info, png_uint_32 length)
    num = (int)length / 2;
 	png_ptr->hist = (png_uint_16p)png_malloc(png_ptr,
 		num * sizeof (png_uint_16));
+   png_ptr->do_free |= PNG_FREE_HIST;
 	for (i = 0; i < num; i++)
    {
       png_byte buf[2];
@@ -417,6 +430,7 @@ png_handle_pHYs(png_structp png_ptr, png_infop info, png_uint_32 length)
 
    if (length != 9)
    {
+		png_warning(png_ptr, "Incorrect pHYs chunk length");
 		png_crc_skip(png_ptr, length);
       return;
 	}
@@ -440,6 +454,7 @@ png_handle_oFFs(png_structp png_ptr, png_infop info, png_uint_32 length)
 
    if (length != 9)
    {
+		png_warning(png_ptr, "Incorrect oFFs chunk length");
 		png_crc_skip(png_ptr, length);
       return;
    }
@@ -462,6 +477,7 @@ png_handle_tIME(png_structp png_ptr, png_infop info, png_uint_32 length)
 
    if (length != 7)
    {
+		png_warning(png_ptr, "Incorrect tIME chunk length");
 		png_crc_skip(png_ptr, length);
       return;
    }
@@ -525,6 +541,7 @@ png_handle_zTXt(png_structp png_ptr, png_infop info, png_uint_32 length)
    /* zTXt can't have zero text */
    if (text == key + (png_size_t)length)
    {
+      png_warning(png_ptr, "Zero length zTXt chunk");
 		png_large_free(png_ptr, key);
       return;
    }
@@ -547,12 +564,17 @@ png_handle_zTXt(png_structp png_ptr, png_infop info, png_uint_32 length)
    key_size = text - key;
    text_size = 0;
 	text = NULL;
+   ret = Z_STREAM_END;
 
    while (png_ptr->zstream->avail_in)
    {
 		ret = inflate(png_ptr->zstream, Z_PARTIAL_FLUSH);
       if (ret != Z_OK && ret != Z_STREAM_END)
       {
+			if (png_ptr->zstream->msg)
+				png_warning(png_ptr, png_ptr->zstream->msg);
+         else
+				png_warning(png_ptr, "zTXt decompression error");
 			inflateReset(png_ptr->zstream);
          png_ptr->zstream->avail_in = 0;
          png_large_free(png_ptr, key);

pngtest.c

@@ -1,9 +1,9 @@
 /* pngtest.c - a simple test program to test libpng 
 
-   libpng 1.0 beta 2 - version 0.81
+   libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+   Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   August 24, 1995
+   January 10, 1996
    */
 
 #include <stdio.h>

pngtrans.c

@@ -2,10 +2,10 @@
 /* pngtrans.c - transforms the data in a row
    routines used by both readers and writers
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
    */
 
 #define PNG_INTERNAL

pngwrite.c

@@ -1,10 +1,10 @@
 
 /* pngwrite.c - general routines to write a png file
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
    */
 
 /* get internal access to png.h */

pngwtran.c

@@ -1,10 +1,10 @@
 
 /* pngwtran.c - transforms the data in a row for png writers
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
    */
 
 #define PNG_INTERNAL

pngwutil.c

@@ -1,10 +1,10 @@
 
 /* pngwutil.c - utilities to write a png file
 
-	libpng 1.0 beta 2 - version 0.85
+	libpng 1.0 beta 2 - version 0.86
    For conditions of distribution and use, see copyright notice in png.h
-   Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
+	Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
-   December 19, 1995
+   January 10, 1996
    */
 #define PNG_INTERNAL
 #include "png.h"

readme.txt

@@ -1,12 +1,8 @@
-readme.txt - for libpng 0.85
+readme.txt - for libpng 0.86
 
 This is a bug fix for the second beta version of libpng 1.0, and
 a first try at a progressive (push) reader.  It hasn't been
-tested very much, but I'm not going to have time to test it for
+tested as much as the pull reader, but seems to work ok.
-a few days, and I wanted to give an advanced look at the
-progressive reader to everyone.  Please report bugs back
-(and fixes, if you find them), and I'll release a new version
-in a week or two.  Thanks.
 
 I've implemented the callback functions for the error/warning
 messages and the input/output.  See the libpng.txt
@@ -44,8 +40,7 @@ be available at the same place you picked up libpng.  If it is
 not there, try ftp.uu.net in the /graphics/png directory.
 
 This code is currently being archived at ftp.uu.net in the
-/graphics/png directory, and at ftp.group42.com (204.94.158.25)
+/graphics/png directory, and on CompuServe, Lib 20 (PNG SUPPORT)
-in the /pub/png directory, and on CompuServe, Lib 20 (PNG SUPPORT)
 at GO GRAPHSUP.  If you can't find it in any of those places,
 e-mail me, and I'll help you find it.
 
@@ -87,5 +82,4 @@ Good luck, and happy coding.
  Internet: schalnat@group42.com
  CompuServe: 75501,1625
  Web: www.group42.com
- FTP: ftp.group42.com (204.94.158.25)