/* 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. */ #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(). */#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 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(png_check_sig(buf, 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). */**** 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 ****void read_png(FILE *fp, unsigned 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;**** 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, (void *)user_error_ptr, user_error_fn, user_warning_fn); if (png_ptr == NULL) { fclose(fp); return; } /* Allocate/initialize the memory for image information. REQUIRED. */ info_ptr = png_create_info_struct(); if (info_ptr == NULL) { fclose(fp); png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL); return; } /* 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 */ png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL); fclose(fp); /* If we get here, we had a problem reading the file */ return; } /* 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); **** 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 */ 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). 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 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 (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 */ 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 (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 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); 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 (display_gamma/viewing_gamma) 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 = 2.2; /* A good guess for a PC monitors in a dimly lit room */ 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. */ int intent; if (png_get_sRGB(png_ptr, info_ptr, &intent) png_set_sRGB(png_ptr, 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, 0.50); /* Dither 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) { png_uint_32 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 dithered */ png_color std_color_cube[MAX_SCREEN_COLORS]; png_set_dither(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))) { 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 */ 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)) { png_color8p sig_bit; png_get_sBIT(png_ptr, info_ptr, &sig_bit); png_set_shift(png_ptr, sig_bit); } /* flip the RGB pixels to BGR (or RGBA to BGRA) */ 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, 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. 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. */ /* The easiest way to read the image: */ png_bytep row_pointers[height]; for (row = 0; row < height; row++) { 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 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); } [[[[[[[ 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 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 - REQUIRED */ png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL); /* close the file */ fclose(fp); /* that's it */ return;} /* 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, (void *)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, (png_infopp)NULL); return ERROR; } if (setjmp((*png_ptr)->jmpbuf)) { png_destroy_read_struct(png_ptr, info_ptr, (png_infopp)NULL); return ERROR; } /* 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). */ 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_ptr)->jmpbuf)) { /* Free the png_ptr and info_ptr memory on error */ png_destroy_read_struct(png_ptr, info_ptr, (png_infopp)NULL); 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. */ 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 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. */} 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; /* open the file */ fp = fopen(file_name, "wb"); 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 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);Lines 1–500 of 687. Load more
/* 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. */ #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(). */ #define PNG_BYTES_TO_CHECK 4 int 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 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(png_check_sig(buf, 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). */ **** 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 **** void read_png(FILE *fp, unsigned 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; **** 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, (void *)user_error_ptr, user_error_fn, user_warning_fn); if (png_ptr == NULL) { fclose(fp); return; } /* Allocate/initialize the memory for image information. REQUIRED. */ info_ptr = png_create_info_struct(); if (info_ptr == NULL) { fclose(fp); png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL); return; } /* 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 */ png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL); fclose(fp); /* If we get here, we had a problem reading the file */ return; } /* 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); **** 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 */ 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). 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 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 (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 */ 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 (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 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); 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 (display_gamma/viewing_gamma) 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 = 2.2; /* A good guess for a PC monitors in a dimly lit room */ 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. */ int intent; if (png_get_sRGB(png_ptr, info_ptr, &intent) png_set_sRGB(png_ptr, 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, 0.50); /* Dither 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) { png_uint_32 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 dithered */ png_color std_color_cube[MAX_SCREEN_COLORS]; png_set_dither(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))) { 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 */ 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)) { png_color8p sig_bit; png_get_sBIT(png_ptr, info_ptr, &sig_bit); png_set_shift(png_ptr, sig_bit); } /* flip the RGB pixels to BGR (or RGBA to BGRA) */ 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, 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. 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. */ /* The easiest way to read the image: */ png_bytep row_pointers[height]; for (row = 0; row < height; row++) { 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 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); } [[[[[[[ 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 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 - REQUIRED */ png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL); /* close the file */ fclose(fp); /* that's it */ return; } /* progressively read a file */ int 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. */ *png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, (void *)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, (png_infopp)NULL); return ERROR; } if (setjmp((*png_ptr)->jmpbuf)) { png_destroy_read_struct(png_ptr, info_ptr, (png_infopp)NULL); return ERROR; } /* 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). */ png_set_progressive_read_fn(*png_ptr, (void *)stream_data, info_callback, row_callback, end_callback); return OK; } int process_data(png_structp *png_ptr, png_infop *info_ptr, png_bytep buffer, png_uint_32 length) { if (setjmp((*png_ptr)->jmpbuf)) { /* Free the png_ptr and info_ptr memory on error */ png_destroy_read_struct(png_ptr, info_ptr, (png_infopp)NULL); 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. */ 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 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. */ } 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; /* open the file */ fp = fopen(file_name, "wb"); 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 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);