#if 0 /* in case someone actually tries to compile this */ /* 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, 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. */ #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)->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 if it isn't a PNG. * * The function check_if_png() shown here, but not used, returns nonzero (true) * if the file can be opened and is a PNG, 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, (png_size_t)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;   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 (ERROR);#else no_open_file /* 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;#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, png_infopp_NULL, png_infopp_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, png_infopp_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() 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 */#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    * dithering, 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, png_voidp_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, int_p_NULL, int_p_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 the    * 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_palette_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_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))      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))      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 = 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 final 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_gamma(png_ptr, screen_gamma, 0.45455);   else   {      double image_gamma;      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, 0.45455);   }    /* 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)   {      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 dithered */         png_color std_color_cube[MAX_SCREEN_COLORS];          png_set_dither(png_ptr, std_color_cube, MAX_SCREEN_COLORS,            MAX_SCREEN_COLORS, png_uint_16p_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_uint_16p histogram = NULL;          png_get_hIST(png_ptr, info_ptr, &histogram);          png_set_dither(png_ptr, palette, num_palette,                        max_screen_colors, histogram, 0);      }   }    /* 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))   {      png_color_8p 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) */   if (color_type & PNG_COLOR_MASK_COLOR)      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] = 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], png_bytepp_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], png_bytepp_NULL,            number_of_rows);#else no_sparkle /* Read the image using the "rectangle" effect */         png_read_rows(png_ptr, png_bytepp_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, png_infopp_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, png_infopp_NULL);      return (ERROR);   }    if (setjmp(png_jmpbuf((*png_ptr))))   {      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.    * 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, 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 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: */

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