pngwutil.c

一个国人自己实现图像库的程序（有参考价值）

/* pngwutil.c - utilities to write a PNG file
 *
 * libpng 1.2.1 - December 12, 2001
 * For conditions of distribution and use, see copyright notice in png.h
 * Copyright (c) 1998-2001 Glenn Randers-Pehrson
 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
 */

#define PNG_INTERNAL
#include "png.h"
#ifdef PNG_WRITE_SUPPORTED

/* Place a 32-bit number into a buffer in PNG byte order.  We work
 * with unsigned numbers for convenience, although one supported
 * ancillary chunk uses signed (two's complement) numbers.
 */
void /* PRIVATE */
png_save_uint_32(png_bytep buf, png_uint_32 i)
{
   buf[0] = (png_byte)((i >> 24) & 0xff);
   buf[1] = (png_byte)((i >> 16) & 0xff);
   buf[2] = (png_byte)((i >> 8) & 0xff);
   buf[3] = (png_byte)(i & 0xff);
}

#if defined(PNG_WRITE_pCAL_SUPPORTED) || defined(PNG_WRITE_oFFs_SUPPORTED)
/* The png_save_int_32 function assumes integers are stored in two's
 * complement format.  If this isn't the case, then this routine needs to
 * be modified to write data in two's complement format.
 */
void /* PRIVATE */
png_save_int_32(png_bytep buf, png_int_32 i)
{
   buf[0] = (png_byte)((i >> 24) & 0xff);
   buf[1] = (png_byte)((i >> 16) & 0xff);
   buf[2] = (png_byte)((i >> 8) & 0xff);
   buf[3] = (png_byte)(i & 0xff);
}
#endif

/* Place a 16-bit number into a buffer in PNG byte order.
 * The parameter is declared unsigned int, not png_uint_16,
 * just to avoid potential problems on pre-ANSI C compilers.
 */
void /* PRIVATE */
png_save_uint_16(png_bytep buf, unsigned int i)
{
   buf[0] = (png_byte)((i >> 8) & 0xff);
   buf[1] = (png_byte)(i & 0xff);
}

/* Write a PNG chunk all at once.  The type is an array of ASCII characters
 * representing the chunk name.  The array must be at least 4 bytes in
 * length, and does not need to be null terminated.  To be safe, pass the
 * pre-defined chunk names here, and if you need a new one, define it
 * where the others are defined.  The length is the length of the data.
 * All the data must be present.  If that is not possible, use the
 * png_write_chunk_start(), png_write_chunk_data(), and png_write_chunk_end()
 * functions instead.
 */
void PNGAPI
png_write_chunk(png_structp png_ptr, png_bytep chunk_name,
   png_bytep data, png_size_t length)
{
   png_write_chunk_start(png_ptr, chunk_name, (png_uint_32)length);
   png_write_chunk_data(png_ptr, data, length);
   png_write_chunk_end(png_ptr);
}

/* Write the start of a PNG chunk.  The type is the chunk type.
 * The total_length is the sum of the lengths of all the data you will be
 * passing in png_write_chunk_data().
 */
void PNGAPI
png_write_chunk_start(png_structp png_ptr, png_bytep chunk_name,
   png_uint_32 length)
{
   png_byte buf[4];
   png_debug2(0, "Writing %s chunk (%lu bytes)\n", chunk_name, length);

   /* write the length */
   png_save_uint_32(buf, length);
   png_write_data(png_ptr, buf, (png_size_t)4);

   /* write the chunk name */
   png_write_data(png_ptr, chunk_name, (png_size_t)4);
   /* reset the crc and run it over the chunk name */
   png_reset_crc(png_ptr);
   png_calculate_crc(png_ptr, chunk_name, (png_size_t)4);
}

/* Write the data of a PNG chunk started with png_write_chunk_start().
 * Note that multiple calls to this function are allowed, and that the
 * sum of the lengths from these calls *must* add up to the total_length
 * given to png_write_chunk_start().
 */
void PNGAPI
png_write_chunk_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
   /* write the data, and run the CRC over it */
   if (data != NULL && length > 0)
   {
      png_calculate_crc(png_ptr, data, length);
      png_write_data(png_ptr, data, length);
   }
}

/* Finish a chunk started with png_write_chunk_start(). */
void PNGAPI
png_write_chunk_end(png_structp png_ptr)
{
   png_byte buf[4];

   /* write the crc */
   png_save_uint_32(buf, png_ptr->crc);

   png_write_data(png_ptr, buf, (png_size_t)4);
}

/* Simple function to write the signature.  If we have already written
 * the magic bytes of the signature, or more likely, the PNG stream is
 * being embedded into another stream and doesn't need its own signature,
 * we should call png_set_sig_bytes() to tell libpng how many of the
 * bytes have already been written.
 */
void /* PRIVATE */
png_write_sig(png_structp png_ptr)
{
   png_byte png_signature[8] = {137, 80, 78, 71, 13, 10, 26, 10};
   /* write the rest of the 8 byte signature */
   png_write_data(png_ptr, &png_signature[png_ptr->sig_bytes],
      (png_size_t)8 - png_ptr->sig_bytes);
   if(png_ptr->sig_bytes < 3)
      png_ptr->mode |= PNG_HAVE_PNG_SIGNATURE;
}

#if defined(PNG_WRITE_TEXT_SUPPORTED) || defined(PNG_WRITE_iCCP_SUPPORTED)
/*
 * This pair of functions encapsulates the operation of (a) compressing a
 * text string, and (b) issuing it later as a series of chunk data writes.
 * The compression_state structure is shared context for these functions
 * set up by the caller in order to make the whole mess thread-safe.
 */

typedef struct
{
    char *input;   /* the uncompressed input data */
    int input_len;   /* its length */
    int num_output_ptr; /* number of output pointers used */
    int max_output_ptr; /* size of output_ptr */
    png_charpp output_ptr; /* array of pointers to output */
} compression_state;

/* compress given text into storage in the png_ptr structure */
static int /* PRIVATE */
png_text_compress(png_structp png_ptr,
        png_charp text, png_size_t text_len, int compression,
        compression_state *comp)
{
   int ret;

   comp->num_output_ptr = comp->max_output_ptr = 0;
   comp->output_ptr = NULL;
   comp->input = NULL;

   /* we may just want to pass the text right through */
   if (compression == PNG_TEXT_COMPRESSION_NONE)
   {
       comp->input = text;
       comp->input_len = text_len;
       return((int)text_len);
   }

   if (compression >= PNG_TEXT_COMPRESSION_LAST)
   {
#if !defined(PNG_NO_STDIO) && !defined(_WIN32_WCE)
      char msg[50];
      sprintf(msg, "Unknown compression type %d", compression);
      png_warning(png_ptr, msg);
#else
      png_warning(png_ptr, "Unknown compression type");
#endif
   }

   /* We can't write the chunk until we find out how much data we have,
    * which means we need to run the compressor first and save the
    * output.  This shouldn't be a problem, as the vast majority of
    * comments should be reasonable, but we will set up an array of
    * malloc'd pointers to be sure.
    *
    * If we knew the application was well behaved, we could simplify this
    * greatly by assuming we can always malloc an output buffer large
    * enough to hold the compressed text ((1001 * text_len / 1000) + 12)
    * and malloc this directly.  The only time this would be a bad idea is
    * if we can't malloc more than 64K and we have 64K of random input
    * data, or if the input string is incredibly large (although this
    * wouldn't cause a failure, just a slowdown due to swapping).
    */

   /* set up the compression buffers */
   png_ptr->zstream.avail_in = (uInt)text_len;
   png_ptr->zstream.next_in = (Bytef *)text;
   png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
   png_ptr->zstream.next_out = (Bytef *)png_ptr->zbuf;

   /* this is the same compression loop as in png_write_row() */
   do
   {
      /* compress the data */
      ret = deflate(&png_ptr->zstream, Z_NO_FLUSH);
      if (ret != Z_OK)
      {
         /* error */
         if (png_ptr->zstream.msg != NULL)
            png_error(png_ptr, png_ptr->zstream.msg);
         else
            png_error(png_ptr, "zlib error");
      }
      /* check to see if we need more room */
      if (!png_ptr->zstream.avail_out && png_ptr->zstream.avail_in)
      {
         /* make sure the output array has room */
         if (comp->num_output_ptr >= comp->max_output_ptr)
         {
            int old_max;

            old_max = comp->max_output_ptr;
            comp->max_output_ptr = comp->num_output_ptr + 4;
            if (comp->output_ptr != NULL)
            {
               png_charpp old_ptr;

               old_ptr = comp->output_ptr;
               comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                  (png_uint_32)(comp->max_output_ptr * sizeof (png_charpp)));
               png_memcpy(comp->output_ptr, old_ptr, old_max
                  * sizeof (png_charp));
               png_free(png_ptr, old_ptr);
            }
            else
               comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                  (png_uint_32)(comp->max_output_ptr * sizeof (png_charp)));
         }

         /* save the data */
         comp->output_ptr[comp->num_output_ptr] = (png_charp)png_malloc(png_ptr,
            (png_uint_32)png_ptr->zbuf_size);
         png_memcpy(comp->output_ptr[comp->num_output_ptr], png_ptr->zbuf,
            png_ptr->zbuf_size);
         comp->num_output_ptr++;

         /* and reset the buffer */
         png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
         png_ptr->zstream.next_out = png_ptr->zbuf;
      }
   /* continue until we don't have any more to compress */
   } while (png_ptr->zstream.avail_in);

   /* finish the compression */
   do
   {
      /* tell zlib we are finished */
      ret = deflate(&png_ptr->zstream, Z_FINISH);

      if (ret == Z_OK)
      {
         /* check to see if we need more room */
         if (!(png_ptr->zstream.avail_out))
         {
            /* check to make sure our output array has room */
            if (comp->num_output_ptr >= comp->max_output_ptr)
            {
               int old_max;

               old_max = comp->max_output_ptr;
               comp->max_output_ptr = comp->num_output_ptr + 4;
               if (comp->output_ptr != NULL)
               {
                  png_charpp old_ptr;

                  old_ptr = comp->output_ptr;
                  /* This could be optimized to realloc() */
                  comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                     (png_uint_32)(comp->max_output_ptr * sizeof (png_charpp)));
                  png_memcpy(comp->output_ptr, old_ptr,
                     old_max * sizeof (png_charp));
                  png_free(png_ptr, old_ptr);
               }
               else
                  comp->output_ptr = (png_charpp)png_malloc(png_ptr,
                     (png_uint_32)(comp->max_output_ptr * sizeof (png_charp)));
            }

            /* save off the data */
            comp->output_ptr[comp->num_output_ptr] =
               (png_charp)png_malloc(png_ptr, (png_uint_32)png_ptr->zbuf_size);
            png_memcpy(comp->output_ptr[comp->num_output_ptr], png_ptr->zbuf,
               png_ptr->zbuf_size);
            comp->num_output_ptr++;

            /* and reset the buffer pointers */
            png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
            png_ptr->zstream.next_out = png_ptr->zbuf;
         }
      }
      else if (ret != Z_STREAM_END)
      {
         /* we got an error */
         if (png_ptr->zstream.msg != NULL)
            png_error(png_ptr, png_ptr->zstream.msg);
         else
            png_error(png_ptr, "zlib error");
      }
   } while (ret != Z_STREAM_END);

   /* text length is number of buffers plus last buffer */
   text_len = png_ptr->zbuf_size * comp->num_output_ptr;
   if (png_ptr->zstream.avail_out < png_ptr->zbuf_size)
      text_len += png_ptr->zbuf_size - (png_size_t)png_ptr->zstream.avail_out;

   return((int)text_len);
}

/* ship the compressed text out via chunk writes */
static void /* PRIVATE */
png_write_compressed_data_out(png_structp png_ptr, compression_state *comp)
{
   int i;

   /* handle the no-compression case */
   if (comp->input)
   {
       png_write_chunk_data(png_ptr, (png_bytep)comp->input,
                            (png_size_t)comp->input_len);
       return;
   }

   /* write saved output buffers, if any */
   for (i = 0; i < comp->num_output_ptr; i++)
   {
      png_write_chunk_data(png_ptr,(png_bytep)comp->output_ptr[i],
         png_ptr->zbuf_size);
      png_free(png_ptr, comp->output_ptr[i]);
      comp->output_ptr[i]=NULL;
   }
   if (comp->max_output_ptr != 0)
      png_free(png_ptr, comp->output_ptr);
      comp->output_ptr=NULL;
   /* write anything left in zbuf */
   if (png_ptr->zstream.avail_out < (png_uint_32)png_ptr->zbuf_size)
      png_write_chunk_data(png_ptr, png_ptr->zbuf,
         png_ptr->zbuf_size - png_ptr->zstream.avail_out);

   /* reset zlib for another zTXt/iTXt or the image data */
   deflateReset(&png_ptr->zstream);

}
#endif

/* Write the IHDR chunk, and update the png_struct with the necessary
 * information.  Note that the rest of this code depends upon this
 * information being correct.
 */
void /* PRIVATE */
png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
   int bit_depth, int color_type, int compression_type, int filter_type,
   int interlace_type)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_IHDR;
#endif
   png_byte buf[13]; /* buffer to store the IHDR info */

   png_debug(1, "in png_write_IHDR\n");
   /* Check that we have valid input data from the application info */
   switch (color_type)
   {
      case PNG_COLOR_TYPE_GRAY:
         switch (bit_depth)
         {
            case 1:
            case 2:
            case 4:
            case 8:
            case 16: png_ptr->channels = 1; break;
            default: png_error(png_ptr,"Invalid bit depth for grayscale image");
         }
         break;
      case PNG_COLOR_TYPE_RGB:
         if (bit_depth != 8 && bit_depth != 16)
            png_error(png_ptr, "Invalid bit depth for RGB image");
         png_ptr->channels = 3;
         break;
      case PNG_COLOR_TYPE_PALETTE:
         switch (bit_depth)
         {
            case 1:
            case 2:
            case 4:
            case 8: png_ptr->channels = 1; break;
            default: png_error(png_ptr, "Invalid bit depth for paletted image");
         }
         break;
      case PNG_COLOR_TYPE_GRAY_ALPHA:
         if (bit_depth != 8 && bit_depth != 16)
            png_error(png_ptr, "Invalid bit depth for grayscale+alpha image");