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#if 0 /* in case someone actually tries to compile this */
/* example.c - an example of using libpng * * Maintained 2018 Cosmin Truta * Maintained 1998-2016 Glenn Randers-Pehrson * Maintained 1996-1997 Andreas Dilger * Written 1995-1996 Guy Eric Schalnat, Group 42, Inc. * * To the extent possible under law, the authors have waived * all copyright and related or neighboring rights to this file. * This work is published from: United States, Canada. */
/* This is an example of how to use libpng to read and write PNG files. * The file libpng-manual.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, is hereby placed * in the public domain, 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; * see also the programs in the contrib directory. */
/* The simple, but restricted approach to reading a PNG file or data stream * requires just two function calls, as in the following complete program. * Writing a file needs just one function call, so long as the data has an * appropriate layout. * * The following code reads PNG image data from a file and writes it, in a * potentially new format, to a new file. While this code will compile, there * is minimal (insufficient) error checking. For a more realistic version, * see contrib/examples/pngtopng.c */
#include <stddef.h>#include <stdlib.h>#include <string.h>#include <stdio.h>#include <png.h>#include <zlib.h>
int main(int argc, const char **argv){ if (argc == 3) { png_image image; /* The control structure used by libpng */
/* Initialize the 'png_image' structure. */ memset(&image, 0, (sizeof image)); image.version = PNG_IMAGE_VERSION;
/* The first argument is the file to read: */ if (png_image_begin_read_from_file(&image, argv[1]) != 0) { png_bytep buffer;
/* Set the format in which to read the PNG file; this code chooses a * simple sRGB format with a non-associated alpha channel, adequate to * store most images. */ image.format = PNG_FORMAT_RGBA;
/* Now allocate enough memory to hold the image in this format; the * PNG_IMAGE_SIZE macro uses the information about the image (width, * height and format) stored in 'image'. */ buffer = malloc(PNG_IMAGE_SIZE(image));
/* If enough memory was available, read the image in the desired * format, then write the result out to the new file. 'background' is * not necessary when reading the image, because the alpha channel is * preserved; if it were to be removed, for example if we requested * PNG_FORMAT_RGB, then either a solid background color would have to * be supplied, or the output buffer would have to be initialized to * the actual background of the image. * * The fourth argument to png_image_finish_read is the 'row_stride' - * this is the number of components allocated for the image in each * row. It has to be at least as big as the value returned by * PNG_IMAGE_ROW_STRIDE, but if you just allocate space for the * default, minimum size, using PNG_IMAGE_SIZE as above, you can pass * zero. * * The final argument is a pointer to a buffer for the colormap; * colormaps have exactly the same format as a row of image pixels * (so you choose what format to make the colormap by setting * image.format). A colormap is only returned if * PNG_FORMAT_FLAG_COLORMAP is also set in image.format, so in this * case NULL is passed as the final argument. If you do want to force * all images into an index/color-mapped format, then you can use: * * PNG_IMAGE_COLORMAP_SIZE(image) * * to find the maximum size of the colormap in bytes. */ if (buffer != NULL && png_image_finish_read(&image, NULL/*background*/, buffer, 0/*row_stride*/, NULL/*colormap*/) != 0) { /* Now write the image out to the second argument. In the write * call 'convert_to_8bit' allows 16-bit data to be squashed down to * 8 bits; this isn't necessary here because the original read was * to the 8-bit format. */ if (png_image_write_to_file(&image, argv[2], 0/*convert_to_8bit*/, buffer, 0/*row_stride*/, NULL/*colormap*/) != 0) { /* The image has been written successfully. */ exit(0); } } else { /* Calling png_image_free is optional unless the simplified API was * not run to completion. In this case, if there wasn't enough * memory for 'buffer', we didn't complete the read, so we must * free the image: */ if (buffer == NULL) png_image_free(&image); else free(buffer); } }
/* Something went wrong reading or writing the image. libpng stores a * textual message in the 'png_image' structure: */ fprintf(stderr, "pngtopng: error: %s\n", image.message); exit(1); }
fprintf(stderr, "pngtopng: usage: pngtopng input-file output-file\n"); exit(2);}
/* That's it ;-) Of course you probably want to do more with PNG files than * just converting them all to 32-bit RGBA PNG files; you can do that between * the call to png_image_finish_read and png_image_write_to_file. You can also * ask for the image data to be presented in a number of different formats. * You do this by simply changing the 'format' parameter set before allocating * the buffer. * * The format parameter consists of five flags that define various aspects of * the image. You can simply add these together to get the format, or you can * use one of the predefined macros from png.h (as above): * * PNG_FORMAT_FLAG_COLOR: if set, the image will have three color components * per pixel (red, green and blue); if not set, the image will just have one * luminance (grayscale) component. * * PNG_FORMAT_FLAG_ALPHA: if set, each pixel in the image will have an * additional alpha value; a linear value that describes the degree the * image pixel covers (overwrites) the contents of the existing pixel on the * display. * * PNG_FORMAT_FLAG_LINEAR: if set, the components of each pixel will be * returned as a series of 16-bit linear values; if not set, the components * will be returned as a series of 8-bit values encoded according to the * sRGB standard. The 8-bit format is the normal format for images intended * for direct display, because almost all display devices do the inverse of * the sRGB transformation to the data they receive. The 16-bit format is * more common for scientific data and image data that must be further * processed; because it is linear, simple math can be done on the component * values. Regardless of the setting of this flag, the alpha channel is * always linear, although it will be 8 bits or 16 bits wide as specified by * the flag. * * PNG_FORMAT_FLAG_BGR: if set, the components of a color pixel will be * returned in the order blue, then green, then red. If not set, the pixel * components are in the order red, then green, then blue. * * PNG_FORMAT_FLAG_AFIRST: if set, the alpha channel (if present) precedes the * color or grayscale components. If not set, the alpha channel follows the * components. * * You do not have to read directly from a file. You can read from memory or, * on systems that support it, from a <stdio.h> FILE*. This is controlled by * the particular png_image_read_from_ function you call at the start. * Likewise, on write, you can write to a FILE* if your system supports it. * Check the macro PNG_STDIO_SUPPORTED to see if stdio support has been * included in your libpng build. * * If you read 16-bit (PNG_FORMAT_FLAG_LINEAR) data, you may need to write it * in the 8-bit format for display. You do this by setting the convert_to_8bit * flag to 'true'. * * Don't repeatedly convert between the 8-bit and 16-bit forms. There is * significant data loss when 16-bit data is converted to the 8-bit encoding, * and the current libpng implementation of conversion to 16-bit is also * significantly lossy. The latter will be fixed in the future, but the former * is unavoidable - the 8-bit format just doesn't have enough resolution. */
/* If your program needs more information from the PNG data it reads, or if you * need to do more complex transformations, or minimize transformations, on the * data you read, then you must use one of the several lower level libpng * interfaces. * * All these interfaces require that you do your own error handling - your * program must be able to arrange for control to return to your own code, any * time libpng encounters a problem. There are several ways to do this, but * the standard way is to use the <setjmp.h> interface to establish a return * point within your own code. You must do this if you do not use the * simplified interface (above). * * The first step is to include the header files you need, including the libpng * header file. Include any standard headers and feature test macros your * program requires before including png.h: */#include <png.h>
/* The png_jmpbuf() macro, used in error handling, became available in * libpng version 1.0.6. If you want to be able to run your code with older * versions of libpng, you must define the macro yourself (but only if it * is not already defined by libpng!) */
#ifndef png_jmpbuf# define png_jmpbuf(png_ptr) ((png_ptr)->png_jmpbuf)#endif
/* Check to see if a file is a PNG file using png_sig_cmp(). png_sig_cmp() * returns zero if the image is a PNG, and nonzero otherwise. * * The function check_if_png() shown here, but not used, returns nonzero (true) * if the file can be opened and is a PNG, and 0 (false) otherwise. * * 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_sig_cmp(), or even skip that if you know * you have a PNG file, and call png_set_sig_bytes(). */#define PNG_BYTES_TO_CHECK 4int check_if_png(char *file_name, FILE **fp){ char buf[PNG_BYTES_TO_CHECK];
/* Open the prospective PNG file. */ if ((*fp = fopen(file_name, "rb")) == NULL) return 0;
/* Read in some of the signature bytes. */ if (fread(buf, 1, PNG_BYTES_TO_CHECK, *fp) != PNG_BYTES_TO_CHECK) return 0;
/* Compare the first PNG_BYTES_TO_CHECK bytes of the signature. * Return nonzero (true) if they match. */ return(!png_sig_cmp(buf, 0, PNG_BYTES_TO_CHECK));}
/* 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). */#ifdef open_file /* prototype 1 */void read_png(char *file_name) /* We need to open the file */{ png_structp png_ptr; png_infop info_ptr; 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 (ERROR);
#else no_open_file /* prototype 2 */void read_png(FILE *fp, int sig_read) /* File is already open */{ png_structp png_ptr; png_infop info_ptr; png_uint_32 width, height; int bit_depth, color_type, interlace_type;#endif no_open_file /* 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 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, png_voidp user_error_ptr, user_error_fn, user_warning_fn);
if (png_ptr == NULL) { fclose(fp); return (ERROR); }
/* Allocate/initialize the memory for image information. REQUIRED. */ info_ptr = png_create_info_struct(png_ptr); if (info_ptr == NULL) { fclose(fp); png_destroy_read_struct(&png_ptr, NULL, NULL); return (ERROR); }
/* 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_jmpbuf(png_ptr))) { /* Free all of the memory associated with the png_ptr and info_ptr. */ png_destroy_read_struct(&png_ptr, &info_ptr, NULL); fclose(fp); /* If we get here, we had a problem reading the file. */ return (ERROR); }
/* One of the following I/O initialization methods is REQUIRED. */#ifdef streams /* PNG file I/O method 1 */ /* Set up the input control if you are using standard C streams. */ png_init_io(png_ptr, fp);
#else no_streams /* PNG file I/O method 2 */ /* If you are using replacement read functions, instead of calling * png_init_io(), 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. */#endif no_streams /* Use only one I/O method! */
/* If we have already read some of the signature */ png_set_sig_bytes(png_ptr, sig_read);
#ifdef hilevel /* If you have enough memory to read in the entire image at once, * and you need to specify only transforms that can be controlled * with one of the PNG_TRANSFORM_* bits (this presently excludes * quantizing, filling, setting background, and doing gamma * adjustment), then you can read the entire image (including * pixels) into the info structure with this call: */ png_read_png(png_ptr, info_ptr, png_transforms, NULL);
#else /* OK, you're doing it the hard way, with the lower-level functions. */
/* 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);
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 bits/color files down to 8 bits/color. * Use accurate scaling if it's available, otherwise just chop off the * low byte. */#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED png_set_scale_16(png_ptr);#else png_set_strip_16(png_ptr);#endif
/* Strip alpha bytes from the input data without combining with the * background (not recommended). */ png_set_strip_alpha(png_ptr);
/* Extract multiple pixels with bit depths of 1, 2 or 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 (color_type == PNG_COLOR_TYPE_PALETTE) png_set_palette_to_rgb(png_ptr);
/* 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_gray_1_2_4_to_8(png_ptr);
/* 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) != 0) png_set_tRNS_to_alpha(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, 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, *image_background;
if (png_get_bKGD(png_ptr, info_ptr, &image_background) != 0) 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);
/* Some suggestions as to how to get a screen gamma value. * * Note that screen gamma is the display_exponent, which includes * the CRT_exponent and any correction for viewing conditions. */ 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("SCREEN_GAMMA")) != NULL) screen_gamma = atof(gamma_str); /* If we don't have another value */ else { screen_gamma = PNG_DEFAULT_sRGB; /* A good guess for a PC monitor in a dimly lit room */ screen_gamma = PNG_GAMMA_MAC_18 or 1.0; /* Good guesses for Mac systems */ }
/* Tell libpng to handle the gamma conversion for you. The final call * is a good guess for PC generated images, but it should be configurable * by the user at run time. Gamma correction support in your application * is strongly recommended. */
int intent;
if (png_get_sRGB(png_ptr, info_ptr, &intent) != 0) png_set_gamma(png_ptr, screen_gamma, PNG_DEFAULT_sRGB); else { double image_gamma; if (png_get_gAMA(png_ptr, info_ptr, &image_gamma) != 0) png_set_gamma(png_ptr, screen_gamma, image_gamma); else png_set_gamma(png_ptr, screen_gamma, 0.45455); }
#ifdef PNG_READ_QUANTIZE_SUPPORTED /* Quantize RGB files down to 8-bit palette, or reduce palettes * to the number of colors available on your screen. */ if ((color_type & PNG_COLOR_MASK_COLOR) != 0) { int num_palette; png_colorp palette;
/* This reduces the image to the application-supplied palette. */ if (/* We have our own palette */) { /* An array of colors to which the image should be quantized. */ png_color std_color_cube[MAX_SCREEN_COLORS]; png_set_quantize(png_ptr, std_color_cube, MAX_SCREEN_COLORS, 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) != 0) { png_uint_16p histogram = NULL; png_get_hIST(png_ptr, info_ptr, &histogram); png_set_quantize(png_ptr, palette, num_palette, max_screen_colors, histogram, 0); } }#endif /* READ_QUANTIZE */
/* Invert monochrome files to have 0 as white and 1 as black. */ png_set_invert_mono(png_ptr);
/* 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) != 0) { png_color_8p sig_bit_p; png_get_sBIT(png_ptr, info_ptr, &sig_bit_p); png_set_shift(png_ptr, sig_bit_p); }
/* Flip the RGB pixels to BGR (or RGBA to BGRA). */ if ((color_type & PNG_COLOR_MASK_COLOR) != 0) png_set_bgr(png_ptr);
/* Swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR). */ png_set_swap_alpha(png_ptr);
/* Swap bytes of 16-bit files to least significant byte first. */ png_set_swap(png_ptr);
/* Add filler (or alpha) byte (before/after each RGB triplet). */ png_set_filler(png_ptr, 0xffff, PNG_FILLER_AFTER);
#ifdef PNG_READ_INTERLACING_SUPPORTED /* 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);#else /* !READ_INTERLACING */ number_passes = 1;#endif /* READ_INTERLACING */
/* 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 (i.e. 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. */ png_bytep row_pointers[height]; for (row = 0; row < height; row++) row_pointers[row] = NULL; /* Clear the pointer array */ for (row = 0; row < height; row++) row_pointers[row] = png_malloc(png_ptr, png_get_rowbytes(png_ptr, info_ptr));
/* Now it's time to read the image. One of these methods is REQUIRED. */#ifdef entire /* Read the entire image in one go */ png_read_image(png_ptr, row_pointers);
#else no_entire /* 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++) {#ifdef single /* Read the image a single row at a time */ for (y = 0; y < height; y++) png_read_rows(png_ptr, &row_pointers[y], NULL, 1);
#else no_single /* Read the image several rows at a time */ for (y = 0; y < height; y += number_of_rows) {#ifdef sparkle /* Read the image using the "sparkle" effect. */ png_read_rows(png_ptr, &row_pointers[y], NULL, number_of_rows);#else no_sparkle /* Read the image using the "rectangle" effect */ png_read_rows(png_ptr, NULL, &row_pointers[y], number_of_rows);#endif no_sparkle /* Use only one of these two methods */ }
/* If you want to display the image after every pass, do so here. */#endif no_single /* Use only one of these two methods */ }#endif no_entire /* Use only one of these two methods */
/* Read rest of file, and get additional chunks in info_ptr. REQUIRED. */ png_read_end(png_ptr, info_ptr);#endif hilevel
/* At this point you have read the entire image. */
/* Clean up after the read, and free any memory allocated. REQUIRED. */ png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
/* Close the file. */ fclose(fp);
/* That's it! */ return (OK);}
/* Progressively read a file */
intinitialize_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. */ *png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, png_voidp user_error_ptr, user_error_fn, user_warning_fn); if (*png_ptr == NULL) { *info_ptr = NULL; return (ERROR); } *info_ptr = png_create_info_struct(png_ptr); if (*info_ptr == NULL) { png_destroy_read_struct(png_ptr, info_ptr, NULL); return (ERROR); } if (setjmp(png_jmpbuf((*png_ptr)))) { png_destroy_read_struct(png_ptr, info_ptr, NULL); return (ERROR); }
/* You will need to provide all three function callbacks, * even if you aren't using all of them. * If you aren't using all functions, you can specify NULL * parameters. Even when all three functions are NULL, * you need to call png_set_progressive_read_fn(). * 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); return (OK);}
intprocess_data(png_structp *png_ptr, png_infop *info_ptr, png_bytep buffer, png_uint_32 length){ if (setjmp(png_jmpbuf((*png_ptr)))) { /* Free the png_ptr and info_ptr memory on error. */ png_destroy_read_struct(png_ptr, info_ptr, NULL); return (ERROR); }
/* Give 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);}
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. */}
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 interlaced, and you turned on the interlace handler, * this function will be called for every row in every pass. * * In this function you will receive a pointer to new row data from * libpng called new_row that is to replace a corresponding row (of * the same data format) in a buffer allocated by your application. * * The new row data pointer "new_row" may be NULL, indicating there is * no new data to be replaced (in cases of interlace loading). * * If new_row is not NULL, then you need to call * png_progressive_combine_row(), to replace the corresponding row as * shown below: */
/* Get pointer to corresponding row in our PNG read buffer. */ png_bytep old_row = ((png_bytep *)our_data)[row_num];
#ifdef PNG_READ_INTERLACING_SUPPORTED /* If both rows are allocated, then copy the new row * data to the corresponding row data. */ if (old_row != NULL && new_row != NULL) png_progressive_combine_row(png_ptr, old_row, new_row);
/* 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 new row and the * old row, as demonstrated above. 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 as new_row, and the function will combine * the old row and the new row. */#endif /* READ_INTERLACING */}
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. */}
/* Write a png file */void write_png(char *file_name /* , ... other image information ... */){ FILE *fp; png_structp png_ptr; png_infop info_ptr; png_colorp palette;
/* Open the file */ fp = fopen(file_name, "wb"); if (fp == NULL) return (ERROR);
/* 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 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, png_voidp user_error_ptr, user_error_fn, user_warning_fn); if (png_ptr == NULL) { fclose(fp); return (ERROR); }
/* Allocate/initialize the image information data. REQUIRED. */ info_ptr = png_create_info_struct(png_ptr); if (info_ptr == NULL) { fclose(fp); png_destroy_write_struct(&png_ptr, NULL); return (ERROR); }
/* Set up error handling. REQUIRED if you aren't supplying your own * error handling functions in the png_create_write_struct() call. */ if (setjmp(png_jmpbuf(png_ptr))) { /* If we get here, we had a problem writing the file. */ fclose(fp); png_destroy_write_struct(&png_ptr, &info_ptr); return (ERROR); }
/* One of the following I/O initialization functions is REQUIRED. */
#ifdef streams /* I/O initialization method 1 */ /* Set up the output control if you are using standard C streams. */ png_init_io(png_ptr, fp);
#else no_streams /* I/O initialization method 2 */ /* If you are using replacement write functions, instead of calling * png_init_io(), 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. */#endif no_streams /* Only use one initialization method */
#ifdef hilevel /* This is the easy way. Use it if you already have all the * image info living in the structure. You could "|" many * PNG_TRANSFORM flags into the png_transforms integer here. */ png_write_png(png_ptr, info_ptr, png_transforms, NULL);
#else /* This is the hard way. */
/* 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. REQUIRED for indexed-color images. */ palette = (png_colorp)png_malloc(png_ptr, PNG_MAX_PALETTE_LENGTH * (sizeof (png_color))); /* ... Set palette colors ... */ png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH); /* You must not free palette here, because png_set_PLTE only makes a link * to the palette that you allocated. Wait until you are about to destroy * the png structure. */
/* Optional significant bit (sBIT) chunk. */ png_color_8 sig_bit;
/* If we are dealing with a grayscale image then */ sig_bit.gray = true_bit_depth;
/* Otherwise, if we are dealing with a color image then */ 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 */ 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. */ png_set_gAMA(png_ptr, info_ptr, gamma);
/* Optionally write comments into the image. */ { png_text text_ptr[3];
char key0[] = "Title"; char text0[] = "Mona Lisa"; text_ptr[0].key = key0; text_ptr[0].text = text0; text_ptr[0].compression = PNG_TEXT_COMPRESSION_NONE; text_ptr[0].itxt_length = 0; text_ptr[0].lang = NULL; text_ptr[0].lang_key = NULL;
char key1[] = "Author"; char text1[] = "Leonardo DaVinci"; text_ptr[1].key = key1; text_ptr[1].text = text1; text_ptr[1].compression = PNG_TEXT_COMPRESSION_NONE; text_ptr[1].itxt_length = 0; text_ptr[1].lang = NULL; text_ptr[1].lang_key = NULL;
char key2[] = "Description"; char text2[] = "<long text>"; text_ptr[2].key = key2; text_ptr[2].text = text2; text_ptr[2].compression = PNG_TEXT_COMPRESSION_zTXt; text_ptr[2].itxt_length = 0; text_ptr[2].lang = NULL; text_ptr[2].lang_key = NULL;
png_set_text(write_ptr, write_info_ptr, text_ptr, 3); }
/* Other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs. */
/* Note that if sRGB is present, the gAMA and cHRM chunks must be ignored * on read and, if your application chooses to write them, they must * be written in accordance with the sRGB profile. */
/* Write the file header information. REQUIRED. */ png_write_info(png_ptr, info_ptr);
/* If you want, you can write the info in two steps, in case you need to * write your private chunk ahead of PLTE: * * png_write_info_before_PLTE(write_ptr, write_info_ptr); * write_my_chunk(); * png_write_info(png_ptr, info_ptr); * * However, given the level of known- and unknown-chunk support in 1.2.0 * and up, this should no longer be necessary. */
/* Once we write out the header, the compression type on the text * chunk 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. */
/* Invert monochrome pixels. */ png_set_invert_mono(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, &sig_bit);
/* Pack pixels into bytes. */ png_set_packing(png_ptr);
/* 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 byte first. */ png_set_swap(png_ptr);
/* Swap bits of 1-bit, 2-bit, 4-bit packed pixel formats. */ png_set_packswap(png_ptr);
/* Turn on interlace handling if you are not using png_write_image(). */ if (interlacing != 0) number_passes = png_set_interlace_handling(png_ptr); else number_passes = 1;
/* 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_uint_32 k, height, width;
/* In this example, "image" is a one-dimensional array of bytes. */
/* Guard against integer overflow. */ if (height > PNG_SIZE_MAX / (width * bytes_per_pixel)) png_error(png_ptr, "Image data buffer would be too large");
png_byte image[height * width * bytes_per_pixel]; png_bytep row_pointers[height];
if (height > PNG_UINT_32_MAX / (sizeof (png_bytep))) png_error(png_ptr, "Image is too tall to process in memory");
/* Set up pointers into your "image" byte array. */ for (k = 0; k < height; k++) row_pointers[k] = image + k * width * bytes_per_pixel;
/* One of the following output methods is REQUIRED. */
#ifdef entire /* 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. */
#else no_entire /* 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. */ png_write_rows(png_ptr, &row_pointers[first_row], number_of_rows);
/* If you are only writing one row at a time, this works. */ for (y = 0; y < height; y++) png_write_rows(png_ptr, &row_pointers[y], 1); }#endif no_entire /* Use only one output method */
/* You can write optional chunks like tEXt, zTXt, and tIME at the end * as well. Shouldn't be necessary in 1.2.0 and up, as all the public * chunks are supported, and you can use png_set_unknown_chunks() to * register unknown chunks into the info structure to be written out. */
/* It is REQUIRED to call this to finish writing the rest of the file. */ png_write_end(png_ptr, info_ptr);#endif hilevel
/* If you png_malloced a palette, free it here. * (Don't free info_ptr->palette, as shown in versions 1.0.5m and earlier of * this example; if libpng mallocs info_ptr->palette, libpng will free it). * If you allocated it with malloc() instead of png_malloc(), use free() * instead of png_free(). */ png_free(png_ptr, palette); palette = NULL;
/* Similarly, if you png_malloced any data that you passed in with * png_set_something(), such as a hist or trans array, free it here, * when you can be sure that libpng is through with it. */ png_free(png_ptr, trans); trans = NULL;
/* Whenever you use png_free(), it is a good idea to set the pointer to * NULL in case your application inadvertently tries to png_free() it * again. When png_free() sees a NULL it returns without action, avoiding * the double-free problem. */
/* Clean up after the write, and free any allocated memory. */ png_destroy_write_struct(&png_ptr, &info_ptr);
/* Close the file. */ fclose(fp);
/* That's it! */ return (OK);}
#endif /* if 0 */