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Imported from libpng-0.97.tar

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Glenn Randers-Pehrson
1998-01-01 07:13:13 -06:00
parent 47a0c422ca
commit b6ce43d6ff
24 changed files with 1297 additions and 763 deletions
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120
example.c
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@@ -1,36 +1,36 @@
/* example.c - an example of using libpng */
/* This is an example of how to use libpng to read and write PNG files.
The file libpng.txt is much more verbose then this. If you have not
read it, do so first. This was designed to be a starting point of an
implementation. This is not officially part of libpng, and therefore
does not require a copyright notice.
This file does not currently compile, because it is missing certain
parts, like allocating memory to hold an image. You will have to
supply these parts to get it to compile. For an example of a minimal
working PNG reader/writer, see pngtest.c, included in this distribution.
*/
* The file libpng.txt is much more verbose then this. If you have not
* read it, do so first. This was designed to be a starting point of an
* implementation. This is not officially part of libpng, and therefore
* does not require a copyright notice.
*
* This file does not currently compile, because it is missing certain
* parts, like allocating memory to hold an image. You will have to
* supply these parts to get it to compile. For an example of a minimal
* working PNG reader/writer, see pngtest.c, included in this distribution.
*/
#include <png.h>
/* Check to see if a file is a PNG file using png_check_sig(). Returns
non-zero if the image is a PNG, and 0 if it isn't a PNG.
If this call is successful, and you are going to keep the file open,
you should call png_set_sig_bytes(png_ptr, PNG_BYTES_TO_CHECK); once
you have created the png_ptr, so that libpng knows your application
has read that many bytes from the start of the file. Make sure you
don't call png_set_sig_bytes() with more than 8 bytes read or give it
an incorrect number of bytes read, or you will either have read too
many bytes (your fault), or you are telling libpng to read the wrong
number of magic bytes (also your fault).
Many applications already read the first 2 or 4 bytes from the start
of the image to determine the file type, so it would be easiest just
to pass the bytes to png_check_sig() or even skip that if you know
you have a PNG file, and call png_set_sig_bytes().
*/
* non-zero if the image is a PNG, and 0 if it isn't a PNG.
*
* If this call is successful, and you are going to keep the file open,
* you should call png_set_sig_bytes(png_ptr, PNG_BYTES_TO_CHECK); once
* you have created the png_ptr, so that libpng knows your application
* has read that many bytes from the start of the file. Make sure you
* don't call png_set_sig_bytes() with more than 8 bytes read or give it
* an incorrect number of bytes read, or you will either have read too
* many bytes (your fault), or you are telling libpng to read the wrong
* number of magic bytes (also your fault).
*
* Many applications already read the first 2 or 4 bytes from the start
* of the image to determine the file type, so it would be easiest just
* to pass the bytes to png_check_sig() or even skip that if you know
* you have a PNG file, and call png_set_sig_bytes().
*/
#define PNG_BYTES_TO_CHECK 4
int check_if_png(char *file_name, FILE **fp)
{
@@ -49,10 +49,11 @@ int check_if_png(char *file_name, FILE **fp)
}
/* Read a PNG file. You may want to return an error code if the read
fails (depending upon the failure). There are two "prototypes" given
here - one where we are given the filename, and we need to open the
file, and the other where we are given an open file (possibly with
some or all of the magic bytes read - see comments above). */
* fails (depending upon the failure). There are two "prototypes" given
* here - one where we are given the filename, and we need to open the
* file, and the other where we are given an open file (possibly with
* some or all of the magic bytes read - see comments above).
*/
**** prototype 1 ****
void read_png(char *file_name) /* We need to open the file */
{
@@ -118,7 +119,8 @@ void read_png(FILE *fp, unsigned int sig_read) /* file is already open */
**** PNG file I/O method 2 ****
/* If you are using replacement read functions, instead of calling
* png_init_io() here you would call */
* png_init_io() here you would call:
*/
png_set_read_fn(png_ptr, (void *)user_io_ptr, user_read_fn);
/* where user_io_ptr is a structure you want available to the callbacks */
**** Use only one I/O method! ****
@@ -143,29 +145,31 @@ void read_png(FILE *fp, unsigned int sig_read) /* file is already open */
/* tell libpng to strip 16 bit/color files down to 8 bits/color */
png_set_strip_16(png_ptr);
/* strip alpha bytes from the input data without combining with th
* background (not recommended) */
/* Strip alpha bytes from the input data without combining with th
* background (not recommended).
*/
png_set_strip_alpha(png_ptr);
/* extract multiple pixels with bit depths of 1, 2, and 4 from a single
/* Extract multiple pixels with bit depths of 1, 2, and 4 from a single
* byte into separate bytes (useful for paletted and grayscale images).
*/
png_set_packing(png_ptr);
/* change the order of packed pixels to least significant bit first
/* Change the order of packed pixels to least significant bit first
* (not useful if you are using png_set_packing). */
png_set_packswap(png_ptr);
/* expand paletted colors into true RGB triplets */
/* Expand paletted colors into true RGB triplets */
if (color_type == PNG_COLOR_TYPE_PALETTE)
png_set_expand(png_ptr);
/* expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel */
/* Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel */
if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
png_set_expand(png_ptr);
/* expand paletted or RGB images with transparency to full alpha channels
* so the data will be available as RGBA quartets */
/* Expand paletted or RGB images with transparency to full alpha channels
* so the data will be available as RGBA quartets.
*/
if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
png_set_expand(png_ptr);
@@ -207,13 +211,17 @@ void read_png(FILE *fp, unsigned int sig_read) /* file is already open */
* by the user at run time by the user. It is strongly suggested that
* your application support gamma correction.
*/
if (png_get_gAMA(png_ptr, info_ptr, &image_gamma);
png_set_gamma(png_ptr, screen_gamma, image_gamma);
else
png_set_gamma(png_ptr, screen_gamma, 0.45);
if (png_get_sRGB(png_ptr, info_ptr, &srgb_intent)
png_set_sRGB(png_ptr, srgb_intent, 0);
else
if (png_get_gAMA(png_ptr, info_ptr, &image_gamma)
png_set_gamma(png_ptr, screen_gamma, image_gamma);
else
png_set_gamma(png_ptr, screen_gamma, 0.45);
/* Dither RGB files down to 8 bit palette or reduce palettes
to the number of colors available on your screen */
* to the number of colors available on your screen.
*/
if (color_type & PNG_COLOR_MASK_COLOR)
{
png_uint_32 num_palette;
@@ -269,19 +277,19 @@ void read_png(FILE *fp, unsigned int sig_read) /* file is already open */
/* Turn on interlace handling. REQUIRED if you are not using
* png_read_image(). To see how to handle interlacing passes,
* see the png_read_row() method below.
* see the png_read_row() method below:
*/
number_passes = png_set_interlace_handling(png_ptr);
/* optional call to gamma correct and add the background to the palette
/* Optional call to gamma correct and add the background to the palette
* and update info structure. REQUIRED if you are expecting libpng to
* update the palette for you (ie you selected such a transform above).
*/
png_read_update_info(png_ptr, info_ptr);
/* allocate the memory to hold the image using the fields of info_ptr. */
/* Allocate the memory to hold the image using the fields of info_ptr. */
/* the easiest way to read the image */
/* The easiest way to read the image: */
png_bytep row_pointers[height];
for (row = 0; row < height; row++)
@@ -294,7 +302,7 @@ void read_png(FILE *fp, unsigned int sig_read) /* file is already open */
png_read_image(png_ptr, row_pointers);
**** Read the image one or more scanlines at a time ****
/* the other way to read images - deal with interlacing */
/* The other way to read images - deal with interlacing: */
for (pass = 0; pass < number_passes; pass++)
{
@@ -552,7 +560,8 @@ void write_png(char *file_name, ... other image information ...)
/* Optional gamma chunk is strongly suggested if you have any guess
* as to the correct gamma of the image. */
* as to the correct gamma of the image.
*/
png_set_gAMA(png_ptr, info_ptr, gamma);
/* Optionally write comments into the image */
@@ -568,6 +577,8 @@ void write_png(char *file_name, ... other image information ...)
png_set_text(png_ptr, info_ptr, text_ptr, 2);
/* other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs, */
/* note that if sRGB is present the cHRM chunk must be ignored
* on read and must be written in accordance with the sRGB profile */
/* Write the file header information. REQUIRED */
png_write_info(png_ptr, info_ptr);
@@ -579,13 +590,15 @@ void write_png(char *file_name, ... other image information ...)
*/
/* set up the transformations you want. Note that these are
* all optional. Only call them if you want them. */
* all optional. Only call them if you want them.
*/
/* invert monocrome pixels */
png_set_invert(png_ptr);
/* Shift the pixels up to a legal bit depth and fill in
* as appropriate to correctly scale the image */
* as appropriate to correctly scale the image.
*/
png_set_shift(png_ptr, &sig_bit);
/* pack pixels into bytes */
@@ -595,7 +608,8 @@ void write_png(char *file_name, ... other image information ...)
png_set_swap_alpha(png_ptr);
/* Get rid of filler (OR ALPHA) bytes, pack XRGB/RGBX/ARGB/RGBA into
* RGB (4 channels -> 3 channels). The second parameter is not used. */
* RGB (4 channels -> 3 channels). The second parameter is not used.
*/
png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
/* flip BGR pixels to RGB */