Imported from libpng-0.96.tar
diff --git a/example.c b/example.c
index 0903933..20510ad 100644
--- a/example.c
+++ b/example.c
@@ -1,92 +1,107 @@
/* 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
+/* 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.
- */
+ 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().
+/* 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_read(png_ptr, 8);
- once you have created the png_ptr, so that libpng knows it
- doesn't have to read the signature again. Make sure you don't
- call png_set_sig_bytes_read() 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). */
-int check_png(char *file_name, FILE **fp)
+ 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)
{
- char buf[8];
- int ret;
+ char buf[PNG_BYTES_TO_CHECK];
- *fp = fopen(file_name, "rb");
- if (!fp)
- return 0;
- ret = fread(buf, 1, 8, *fp);
-
- if (ret != 8)
+ /* Open the prospective PNG file. */
+ if ((*fp = fopen(file_name, "rb")) != NULL);
return 0;
- /* Check the signature starting at byte 0, and check all 8 bytes */
- ret = png_check_sig(buf, 0, 8);
+ /* Read in the signature bytes */
+ if (fread(buf, 1, PNG_BYTES_TO_CHECK, *fp) != PNG_BYTES_TO_CHECK)
+ return 0;
- return (ret);
+ /* Compare the first PNG_BYTES_TO_CHECK bytes of the signature. */
+ return(png_check_sig(buf, PNG_BYTES_TO_CHECK));
}
-/* read a png file. You may want to return an error code if the read
+/* 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 above) and an opened file
- for reading. */
-------- prototype 1 ----------
+ 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 */
{
png_structp png_ptr;
png_infop info_ptr;
+ unsigned int sig_read = 0;
+ png_uint_32 width, height;
+ int bit_depth, color_type, interlace_type;
FILE *fp;
if ((fp = fopen(file_name, "rb")) == NULL)
return;
-------- prototype 2 ----------
+**** prototype 2 ****
void read_png(FILE *fp, unsigned int sig_read) /* file is already open */
{
png_structp png_ptr;
png_infop info_ptr;
-------- only use one! --------
+ png_uint_32 width, height;
+ int bit_depth, color_type, interlace_type;
+**** only use one prototype! ****
/* Create and initialize the png_struct with the desired error handler
- functions. If you want to use the default stderr and longjump method,
- you can supply NULL for the last three parameters. We also check that
- the header file is compatible with the library version. */
+ * functions. If you want to use the default stderr and longjump method,
+ * you can supply NULL for the last three parameters. We also supply the
+ * the compiler header file version, so that we know if the application
+ * was compiled with a compatible version of the library. REQUIRED
+ */
png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
(void *)user_error_ptr, user_error_fn, user_warning_fn);
- if (!png_ptr)
+ if (png_ptr == NULL)
{
fclose(fp);
return;
}
+ /* Allocate/initialize the memory for image information. REQUIRED. */
info_ptr = png_create_info_struct();
- if (!info_ptr)
+ if (info_ptr == NULL)
{
fclose(fp);
- png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
+ png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
return;
}
- /* set error handling if you are using the setjmp/longjmp method */
+ /* Set error handling if you are using the setjmp/longjmp method (this is
+ * the normal method of doing things with libpng). REQUIRED unless you
+ * set up your own error handlers in the png_create_read_struct() earlier.
+ */
if (setjmp(png_ptr->jmpbuf))
{
/* Free all of the memory associated with the png_ptr and info_ptr */
@@ -96,152 +111,221 @@
return;
}
- /* set up the input control if you are using standard C streams */
+ /* One of the following I/O initialization methods is REQUIRED */
+**** PNG file I/O method 1 ****
+ /* 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, instead of calling
- png_init_io() here you would call */
+**** PNG file I/O method 2 ****
+ /* If you are using replacement read functions, instead of calling
+ * 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! ****
- /* if we have already read some of the signature from the beginning call */
+ /* If we have already read some of the signature */
png_set_sig_bytes_read(png_ptr, sig_read);
- /* The call to png_read_info() gives us all of the information
- from the PNG file before the first IDAT (image data chunk). */
+ /* The call to png_read_info() gives us all of the information from the
+ * PNG file before the first IDAT (image data chunk). REQUIRED
+ */
png_read_info(png_ptr, info_ptr);
- /* set up the transformations you want. Note that these are
- all optional. Only call them if you want them */
+ png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
+ &interlace_type, NULL, NULL);
+
+/**** Set up the data transformations you want. Note that these are all
+ **** optional. Only call them if you want/need them. Many of the
+ **** transformations only work on specific types of images, and many
+ **** are mutually exclusive.
+ ****/
+
+ /* 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) */
+ png_set_strip_alpha(png_ptr);
+
+ /* 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
+ * (not useful if you are using png_set_packing). */
+ png_set_packswap(png_ptr);
/* expand paletted colors into true RGB triplets */
- if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
+ if (color_type == PNG_COLOR_TYPE_PALETTE)
png_set_expand(png_ptr);
- /* expand grayscale images to the full 8 bits */
- if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY && info_ptr->bit_depth < 8)
+ /* 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 */
- if (info_ptr->valid & PNG_INFO_tRNS)
+ if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
png_set_expand(png_ptr);
- /* Set the background color to draw transparent and alpha
- images over. It is possible to set the red, green, and blue
- components directly for paletted images. */
+ /* Set the background color to draw transparent and alpha images over.
+ * It is possible to set the red, green, and blue components directly
+ * for paletted images instead of supplying a palette index. Note that
+ * even if the PNG file supplies a background, you are not required to
+ * use it - you should use the (solid) application background if it has one.
+ */
- png_color_16 my_background;
+ png_color_16 my_background, *image_background);
- if (info_ptr->valid & PNG_INFO_bKGD)
- png_set_background(png_ptr, &(info_ptr->background),
+ if (png_get_bKGD(png_ptr, info_ptr, &image_background);
+ png_set_background(png_ptr, image_background),
PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
else
png_set_background(png_ptr, &my_background,
PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
- /* tell libpng to handle the gamma conversion for you. We only
- need the second call if the screen_gamma isn't the usual 2.2
- or if it is controllable by the user. It may also be a good
- idea to allow the user to set the file gamma if it is unknown. */
- if (info_ptr->valid & PNG_INFO_gAMA)
- png_set_gamma(png_ptr, screen_gamma, info_ptr->gamma);
+ /* Some suggestions as to how to get a screen gamma value */
+ if (/* We have a user-defined screen gamma value */)
+ {
+ screen_gamma = user-defined screen_gamma;
+ }
+ /* This is one way that applications share the same screen gamma value */
+ else if ((gamma_str = getenv("DISPLAY_GAMMA")) != NULL)
+ {
+ screen_gamma = atof(gamma_str);
+ }
+ /* If we don't have another value */
+ else
+ {
+ screen_gamma = 2.2; /* A good guess for PC monitors */
+ screen_gamma = 1.7 or 1.0; /* A good guess for Mac systems */
+ }
+
+ /* Tell libpng to handle the gamma conversion for you. The second call
+ * is a good guess for PC generated images, but it should be configurable
+ * 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);
- /* tell libpng to strip 16 bit/color files down to 8 bits/color */
- if (info_ptr->bit_depth == 16)
- png_set_strip_16(png_ptr);
-
- /* dither rgb files down to 8 bit palette & reduce palettes
+ /* Dither RGB files down to 8 bit palette or reduce palettes
to the number of colors available on your screen */
- if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
+ if (color_type & PNG_COLOR_MASK_COLOR)
{
- if (info_ptr->valid & PNG_INFO_PLTE)
- png_set_dither(png_ptr, info_ptr->palette, info_ptr->num_palette,
- max_screen_colors, info_ptr->histogram);
- else
+ png_uint_32 num_palette;
+ png_colorp palette;
+
+ /* This reduces the image to the application supplied palette */
+ if (we have our own palette)
{
- png_color std_color_cube[MAX_SCREEN_COLORS] =
- {/* ... colors ... */};
+ /* An array of colors to which the image should be dithered */
+ png_color std_color_cube[MAX_SCREEN_COLORS];
png_set_dither(png_ptr, std_color_cube, MAX_SCREEN_COLORS,
- MAX_SCREEN_COLORS, NULL);
+ MAX_SCREEN_COLORS, NULL, 0);
+ }
+ /* This reduces the image to the palette supplied in the file */
+ else if (png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette)))
+ {
+ png_color16p histogram;
+
+ png_get_hIST(png_ptr, info_ptr, &histogram);
+
+ png_set_dither(png_ptr, palette, num_palette,
+ max_screen_colors, histogram, 0);
}
}
/* invert monocrome files to have 0 as white and 1 as black */
- if (info_ptr->bit_depth == 1 && info_ptr->color_type == PNG_COLOR_GRAY)
- png_set_invert(png_ptr);
+ png_set_invert(png_ptr);
- /* shift the pixels down to their true bit depth */
- if (info_ptr->valid & PNG_INFO_sBIT &&
- info_ptr->bit_depth > info_ptr->sig_bit)
- png_set_shift(png_ptr, &(info_ptr->sig_bit));
+ /* If you want to shift the pixel values from the range [0,255] or
+ * [0,65535] to the original [0,7] or [0,31], or whatever range the
+ * colors were originally in:
+ */
+ if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sBIT))
+ {
+ png_color8p sig_bit;
- /* pack multiple pixels with bit depths of 1, 2, and 4 into bytes
- (useful only for paletted and grayscale images) */
- if (info_ptr->bit_depth < 8)
- png_set_packing(png_ptr);
+ png_get_sBIT(png_ptr, info_ptr, &sig_bit);
+ png_set_shift(png_ptr, sig_bit);
+ }
- /* flip the rgb pixels to bgr */
- if (info_ptr->color_type == PNG_COLOR_TYPE_RGB ||
- info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
- png_set_bgr(png_ptr);
+ /* flip the RGB pixels to BGR (or RGBA to BGRA) */
+ png_set_bgr(png_ptr);
- /* swap bytes of 16 bit files to least significant bit first */
- if (info_ptr->bit_depth == 16)
- png_set_swap(png_ptr);
+ /* swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */
+ png_set_swap_alpha(png_ptr);
- /* add a filler byte to RGB files (before or after each RGB triplet) */
- if (info_ptr->bit_depth == 8 && info_ptr->color_type == PNG_COLOR_TYPE_RGB)
- png_set_filler(png_ptr, 0xff, PNG_FILLER_AFTER);
+ /* swap bytes of 16 bit files to least significant byte first */
+ png_set_swap(png_ptr);
- /* turn on interlace handling if you are not using png_read_image() */
+ /* Add filler (or alpha) byte (before/after each RGB triplet) */
+ png_set_filler(png_ptr, 0xff, PNG_FILLER_AFTER);
+
+ /* 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.
+ */
number_passes = png_set_interlace_handling(png_ptr);
/* optional call to gamma correct and add the background to the palette
- and update info structure. */
+ * 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 png_info. */
+ /* allocate the memory to hold the image using the fields of info_ptr. */
/* the easiest way to read the image */
png_bytep row_pointers[height];
for (row = 0; row < height; row++)
{
- row_pointers[row] = malloc(info_ptr->rowbytes);
+ row_pointers[row] = malloc(png_get_rowbytes(png_ptr, info_ptr));
}
+ /* Now it's time to read the image. One of these methods is REQUIRED */
+**** Read the entire image in one go ****
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 */
for (pass = 0; pass < number_passes; pass++)
{
- /* Read the image using the "sparkle" effect. */
- png_read_rows(png_ptr, row_pointers, NULL, number_of_rows);
-
- /* If you are only reading on row at a time, this works */
+[[[[[[[ Read the image a single row at a time ]]]]]]]
for (y = 0; y < height; y++)
{
png_bytep row_pointers = row[y];
png_read_rows(png_ptr, &row_pointers, NULL, 1);
}
- /* to get the rectangle effect, use the third parameter */
- png_read_rows(png_ptr, NULL, row_pointers, number_of_rows);
-
+[[[[[[[ Read the image several rows at a time ]]]]]]]
+ for (y = 0; y < height; y += number_of_rows)
+ {
+<<<<<<<<<< Read the image using the "sparkle" effect. >>>>>>>>>>
+ png_read_rows(png_ptr, row_pointers, NULL, number_of_rows);
+
+<<<<<<<<<< Read the image using the "rectangle" effect >>>>>>>>>>
+ png_read_rows(png_ptr, NULL, row_pointers, number_of_rows);
+<<<<<<<<<< use only one of these two methods >>>>>>>>>>
+ }
+
/* if you want to display the image after every pass, do
so here */
+[[[[[[[ use only one of these two methods ]]]]]]]
}
+**** use only one of these two methods ****
- /* read the rest of the file, getting any additional chunks in info_ptr */
+ /* read rest of file, and get additional chunks in info_ptr - REQUIRED */
png_read_end(png_ptr, info_ptr);
- /* clean up after the read, and free any memory allocated */
+ /* clean up after the read, and free any memory allocated - REQUIRED */
png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);
/* close the file */
@@ -257,15 +341,15 @@
initialize_png_reader(png_structp *png_ptr, png_infop *info_ptr)
{
/* Create and initialize the png_struct with the desired error handler
- functions. If you want to use the default stderr and longjump method,
- you can supply NULL for the last three parameters. We also check that
- the library version is compatible in case we are using dynamically
- linked libraries.
+ * functions. If you want to use the default stderr and longjump method,
+ * you can supply NULL for the last three parameters. We also check that
+ * the library version is compatible in case we are using dynamically
+ * linked libraries.
*/
*png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
(void *)user_error_ptr, user_error_fn, user_warning_fn);
- if (! *png_ptr)
+ if (*png_ptr == NULL)
{
*info_ptr = NULL;
return ERROR;
@@ -273,7 +357,7 @@
*info_ptr = png_create_info_struct(png_ptr);
- if (! *info_ptr)
+ if (*info_ptr == NULL)
{
png_destroy_read_struct(png_ptr, info_ptr, (png_infopp)NULL);
return ERROR;
@@ -286,13 +370,14 @@
}
/* this one's new. You will need to provide all three
- function callbacks, even if you aren't using them all.
- These functions shouldn't be dependent on global or
- static variables if you are decoding several images
- simultaneously. You should store stream specific data
- in a separate struct, given as the second parameter,
- and retrieve the pointer from inside the callbacks using
- the function png_get_progressive_ptr(png_ptr). */
+ * function callbacks, even if you aren't using them all.
+ * These functions shouldn't be dependent on global or
+ * static variables if you are decoding several images
+ * simultaneously. You should store stream specific data
+ * in a separate struct, given as the second parameter,
+ * and retrieve the pointer from inside the callbacks using
+ * the function png_get_progressive_ptr(png_ptr).
+ */
png_set_progressive_read_fn(*png_ptr, (void *)stream_data,
info_callback, row_callback, end_callback);
@@ -310,15 +395,16 @@
return ERROR;
}
- /* this one's new also. Simply give it chunks of data as
- they arrive from the data stream (in order, of course).
- On Segmented machines, don't give it any more than 64K.
- The library seems to run fine with sizes of 4K, although
- you can give it much less if necessary (I assume you can
- give it chunks of 1 byte, but I haven't tried with less
- than 256 bytes yet). When this function returns, you may
- want to display any rows that were generated in the row
- callback, if you aren't already displaying them there. */
+ /* This one's new also. Simply give it chunks of data as
+ * they arrive from the data stream (in order, of course).
+ * On Segmented machines, don't give it any more than 64K.
+ * The library seems to run fine with sizes of 4K, although
+ * you can give it much less if necessary (I assume you can
+ * give it chunks of 1 byte, but I haven't tried with less
+ * than 256 bytes yet). When this function returns, you may
+ * want to display any rows that were generated in the row
+ * callback, if you aren't already displaying them there.
+ */
png_process_data(*png_ptr, *info_ptr, buffer, length);
return OK;
}
@@ -326,52 +412,56 @@
info_callback(png_structp png_ptr, png_infop info)
{
/* do any setup here, including setting any of the transformations
- mentioned in the Reading PNG files section. For now, you _must_
- call either png_start_read_image() or png_read_update_info()
- after all the transformations are set (even if you don't set
- any). You may start getting rows before png_process_data()
- returns, so this is your last chance to prepare for that. */
+ * mentioned in the Reading PNG files section. For now, you _must_
+ * call either png_start_read_image() or png_read_update_info()
+ * after all the transformations are set (even if you don't set
+ * any). You may start getting rows before png_process_data()
+ * returns, so this is your last chance to prepare for that.
+ */
}
row_callback(png_structp png_ptr, png_bytep new_row,
png_uint_32 row_num, int pass)
{
/* this function is called for every row in the image. If the
- image is interlacing, and you turned on the interlace handler,
- this function will be called for every row in every pass.
- Some of these rows will not be changed from the previous pass.
- When the row is not changed, the new_row variable will be NULL.
- The rows and passes are called in order, so you don't really
- need the row_num and pass, but I'm supplying them because it
- may make your life easier.
-
- For the non-NULL rows of interlaced images, you must call
- png_progressive_combine_row() passing in the row and the
- old row. You can call this function for NULL rows (it will
- just return) and for non-interlaced images (it just does the
- memcpy for you) if it will make the code easier. Thus, you
- can just do this for all cases: */
+ * image is interlacing, and you turned on the interlace handler,
+ * this function will be called for every row in every pass.
+ * Some of these rows will not be changed from the previous pass.
+ * When the row is not changed, the new_row variable will be NULL.
+ * The rows and passes are called in order, so you don't really
+ * need the row_num and pass, but I'm supplying them because it
+ * may make your life easier.
+ *
+ * For the non-NULL rows of interlaced images, you must call
+ * png_progressive_combine_row() passing in the row and the
+ * old row. You can call this function for NULL rows (it will
+ * just return) and for non-interlaced images (it just does the
+ * memcpy for you) if it will make the code easier. Thus, you
+ * can just do this for all cases:
+ */
png_progressive_combine_row(png_ptr, old_row, new_row);
/* where old_row is what was displayed for previous rows. Note
- that the first pass (pass == 0 really) will completely cover
- the old row, so the rows do not have to be initialized. After
- the first pass (and only for interlaced images), you will have
- to pass the current row, and the function will combine the
- old row and the new row. */
+ * that the first pass (pass == 0 really) will completely cover
+ * the old row, so the rows do not have to be initialized. After
+ * the first pass (and only for interlaced images), you will have
+ * to pass the current row, and the function will combine the
+ * old row and the new row.
+ */
}
end_callback(png_structp png_ptr, png_infop info)
{
/* this function is called when the whole image has been read,
- including any chunks after the image (up to and including
- the IEND). You will usually have the same info chunk as you
- had in the header, although some data may have been added
- to the comments and time fields.
-
- Most people won't do much here, perhaps setting a flag that
- marks the image as finished. */
+ * including any chunks after the image (up to and including
+ * the IEND). You will usually have the same info chunk as you
+ * had in the header, although some data may have been added
+ * to the comments and time fields.
+ *
+ * Most people won't do much here, perhaps setting a flag that
+ * marks the image as finished.
+ */
}
/* write a png file */
@@ -383,33 +473,36 @@
/* open the file */
fp = fopen(file_name, "wb");
- if (!fp)
+ if (fp == NULL)
return;
/* Create and initialize the png_struct with the desired error handler
- functions. If you want to use the default stderr and longjump method,
- you can supply NULL for the last three parameters. We also check that
- the library version is compatible in case we are using dynamically
- linked libraries.
+ * functions. If you want to use the default stderr and longjump method,
+ * you can supply NULL for the last three parameters. We also check that
+ * the library version is compatible with the one used at compile time,
+ * in case we are using dynamically linked libraries. REQUIRED.
*/
png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,
(void *)user_error_ptr, user_error_fn, user_warning_fn);
- if (!png_ptr)
+ if (png_ptr == NULL)
{
fclose(fp);
return;
}
+ /* Allocate/initialize the image information data. REQUIRED */
info_ptr = png_create_info_struct(png_ptr);
- if (!info_ptr)
+ if (info_ptr == NULL)
{
fclose(fp);
png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
return;
}
- /* set error handling */
+ /* Set error handling. REQUIRED if you aren't supplying your own
+ * error hadnling functions in the png_create_write_struct() call.
+ */
if (setjmp(png_ptr->jmpbuf))
{
/* If we get here, we had a problem reading the file */
@@ -418,63 +511,101 @@
return;
}
+ /* One of the following I/O initialization functions is REQUIRED */
+**** I/O initialization method 1 ****
/* set up the output control if you are using standard C streams */
png_init_io(png_ptr, fp);
+**** I/O initialization method 2 ****
+ /* If you are using replacement read functions, instead of calling
+ * png_init_io() here you would call */
+ png_set_write_fn(png_ptr, (void *)user_io_ptr, user_write_fn,
+ user_IO_flush_function);
+ /* where user_io_ptr is a structure you want available to the callbacks */
+**** only use 1 initialization method ****
- /* set the file information here */
- info_ptr->width = ;
- info_ptr->height = ;
- etc.
+ /* Set the image information here. Width and height are up to 2^31,
+ * bit_depth is one of 1, 2, 4, 8, or 16, but valid values also depend on
+ * the color_type selected. color_type is one of PNG_COLOR_TYPE_GRAY,
+ * PNG_COLOR_TYPE_GRAY_ALPHA, PNG_COLOR_TYPE_PALETTE, PNG_COLOR_TYPE_RGB,
+ * or PNG_COLOR_TYPE_RGB_ALPHA. interlace is either PNG_INTERLACE_NONE or
+ * PNG_INTERLACE_ADAM7, and the compression_type and filter_type MUST
+ * currently be PNG_COMPRESSION_TYPE_BASE and PNG_FILTER_TYPE_BASE. REQUIRED
+ */
+ png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth, PNG_COLOR_TYPE_???,
+ PNG_INTERLACE_????, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
- /* set the palette if there is one */
- info_ptr->valid |= PNG_INFO_PLTE;
- info_ptr->palette = malloc(256 * sizeof (png_color));
- info_ptr->num_palette = 256;
+ /* set the palette if there is one. REQUIRED for indexed-color images */
+ palette = png_malloc(png_ptr, 256 * sizeof (png_color));
... set palette colors ...
+ png_set_PLTE(png_ptr, info_ptr, palette, 256);
/* optional significant bit chunk */
- info_ptr->valid |= PNG_INFO_sBIT;
/* if we are dealing with a grayscale image then */
- info_ptr->sig_bit.gray = true_bit_depth;
+ 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;
+ sig_bit.red = true_red_bit_depth;
+ sig_bit.green = true_green_bit_depth;
+ sig_bit.blue = true_blue_bit_depth;
/* if the image has an alpha channel then */
- info_ptr->sig_bit.alpha = true_alpha_bit_depth;
+ sig_bit.alpha = true_alpha_bit_depth;
+ png_set_sBIT(png_ptr, info_ptr, sig_bit);
+
- /* 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;
+ /* Optional gamma chunk is strongly suggested if you have any guess
+ * as to the correct gamma of the image. */
+ png_set_gAMA(png_ptr, info_ptr, gamma);
- /* other optional chunks like cHRM, bKGD, tRNS, tEXt, tIME, oFFs, pHYs, */
+ /* Optionally write comments into the image */
+ text_ptr[0].key = "Title";
+ text_ptr[0].text = "Mona Lisa";
+ text_ptr[0].compression = PNG_TEXT_COMPRESSION_NONE;
+ text_ptr[1].key = "Author";
+ text_ptr[1].text = "Leonardo DaVinci";
+ text_ptr[1].compression = PNG_TEXT_COMPRESSION_NONE;
+ text_ptr[2].key = "Description";
+ text_ptr[2].text = "<long text>";
+ text_ptr[2].compression = PNG_TEXT_COMPRESSION_zTXt;
+ png_set_text(png_ptr, info_ptr, text_ptr, 2);
- /* write the file header information */
+ /* other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs, */
+
+ /* Write the file header information. REQUIRED */
png_write_info(png_ptr, info_ptr);
+ /* Once we write out the header, the compression type on the text
+ * chunks gets changed to PNG_TEXT_COMPRESSION_NONE_WR or
+ * PNG_TEXT_COMPRESSION_zTXt_WR, so it doesn't get written out again
+ * at the end.
+ */
+
/* 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 */
- png_set_shift(png_ptr, &(info_ptr->sig_bit));
+ /* Shift the pixels up to a legal bit depth and fill in
+ * as appropriate to correctly scale the image */
+ png_set_shift(png_ptr, &sig_bit);
/* pack pixels into bytes */
png_set_packing(png_ptr);
- /* flip bgr pixels to rgb */
+ /* swap location of alpha bytes from ARGB to RGBA */
+ 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. */
+ png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
+
+ /* flip BGR pixels to RGB */
png_set_bgr(png_ptr);
- /* swap bytes of 16 bit files to most significant bit first */
+ /* swap bytes of 16-bit files to most significant byte first */
png_set_swap(png_ptr);
- /* get rid of filler bytes, pack rgb into 3 bytes. The
- filler number is not used. */
- png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
+ /* swap bits of 1, 2, 4 bit packed pixel formats */
+ png_set_packswap(png_ptr);
/* turn on interlace handling if you are not using png_write_image() */
if (interlacing)
@@ -482,14 +613,22 @@
else
number_passes = 1;
- /* the easiest way to write the image (you may choose to allocate the
- memory differently, however) */
+ /* The easiest way to write the image (you may have a different memory
+ * layout, however, so choose what fits your needs best). You need to
+ * use the first method if you aren't handling interlacing yourself.
+ */
png_byte row_pointers[height][width];
+ /* One of the following output methods is REQUIRED */
+**** write out the entire image data in one call ***
png_write_image(png_ptr, row_pointers);
/* the other way to write the image - deal with interlacing */
+**** write out the image data by one or more scanlines ****
+ /* The number of passes is either 1 for non-interlaced images,
+ * or 7 for interlaced images.
+ */
for (pass = 0; pass < number_passes; pass++)
{
/* Write a few rows at a time. */
@@ -502,24 +641,22 @@
png_write_rows(png_ptr, &row_pointers, 1);
}
}
+**** use only one output method ****
- /* You can write optional chunks like tEXt, tIME at the end as well.
- * Note that if you wrote tEXt or zTXt chunks before the image, and
- * you aren't writing out more at the end, you have to set
- * info_ptr->num_text = 0 or they will be written out again.
+ /* You can write optional chunks like tEXt, zTXt, and tIME at the end
+ * as well.
*/
- /* write the rest of the file */
+ /* It is REQUIRED to call this to finish writing the rest of the file */
png_write_end(png_ptr, info_ptr);
/* if you malloced the palette, free it here */
- if (info_ptr->palette)
- free(info_ptr->palette);
+ free(info_ptr->palette);
/* if you allocated any text comments, free them here */
/* clean up after the write, and free any memory allocated */
- png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
+ png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
/* close the file */
fclose(fp);
