    /*
     * jdatadst.c
     *
     * Copyright (C) 1994-1996, Thomas G. Lane.
     * This file is part of the Independent JPEG Group's software.
     * For conditions of distribution and use, see the accompanying README file.
     *
     * This file contains compression data destination routines for the case of
     * emitting JPEG data to a file (or any stdio stream).  While these routines
     * are sufficient for most applications, some will want to use a different
     * destination manager.
     * IMPORTANT: we assume that fwrite() will correctly transcribe an array of
     * JOCTETs into 8-bit-wide elements on external storage.  If char is wider
     * than 8 bits on your machine, you may need to do some tweaking.
     */

    /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
    #include "jinclude.h"
    #include "jpeglib.h"
    #include "jerror.h"

    /* Expanded data destination object for stdio output */

    typedef struct {
      struct jpeg_destination_mgr pub; /* public fields */

      FILE * outfile;		/* target stream */
      JOCTET * buffer;		/* start of buffer */
    } my_destination_mgr;

    typedef my_destination_mgr * my_dest_ptr;

    #define OUTPUT_BUF_SIZE  4096	/* choose an efficiently fwrite'able size */

    /*
     * Initialize destination --- called by jpeg_start_compress
     * before any data is actually written.
     */

    METHODDEF(void)
    init_destination (j_compress_ptr cinfo)
    {
      my_dest_ptr dest = (my_dest_ptr) cinfo->dest;

      /* Allocate the output buffer --- it will be released when done with image */
      dest->buffer = (JOCTET *)
          (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
    				  OUTPUT_BUF_SIZE * SIZEOF(JOCTET));

      dest->pub.next_output_byte = dest->buffer;
      dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
    }

    /*
     * Empty the output buffer --- called whenever buffer fills up.
     *
     * In typical applications, this should write the entire output buffer
     * (ignoring the current state of next_output_byte & free_in_buffer),
     * reset the pointer & count to the start of the buffer, and return TRUE
     * indicating that the buffer has been dumped.
     *
     * In applications that need to be able to suspend compression due to output
     * overrun, a FALSE return indicates that the buffer cannot be emptied now.
     * In this situation, the compressor will return to its caller (possibly with
     * an indication that it has not accepted all the supplied scanlines).  The
     * application should resume compression after it has made more room in the
     * output buffer.  Note that there are substantial restrictions on the use of
     * suspension --- see the documentation.
     *
     * When suspending, the compressor will back up to a convenient restart point
     * (typically the start of the current MCU). next_output_byte & free_in_buffer
     * indicate where the restart point will be if the current call returns FALSE.
     * Data beyond this point will be regenerated after resumption, so do not
     * write it out when emptying the buffer externally.
     */

    METHODDEF(int)
    empty_output_buffer (j_compress_ptr cinfo)
    {
      my_dest_ptr dest = (my_dest_ptr) cinfo->dest;

      if (JFWRITE(dest->outfile, dest->buffer, OUTPUT_BUF_SIZE) !=
          (size_t) OUTPUT_BUF_SIZE)
        ERREXIT(cinfo, JERR_FILE_WRITE);

      dest->pub.next_output_byte = dest->buffer;
      dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;

      return TRUE;
    }

    /*
     * Terminate destination --- called by jpeg_finish_compress
     * after all data has been written.  Usually needs to flush buffer.
     *
     * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
     * application must deal with any cleanup that should happen even
     * for error exit.
     */

    METHODDEF(void)
    term_destination (j_compress_ptr cinfo)
    {
      my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
      size_t datacount = OUTPUT_BUF_SIZE - dest->pub.free_in_buffer;

      /* Write any data remaining in the buffer */
      if (datacount > 0) {
        if (JFWRITE(dest->outfile, dest->buffer, datacount) != datacount)
          ERREXIT(cinfo, JERR_FILE_WRITE);
      }
      fflush(dest->outfile);
      /* Make sure we wrote the output file OK */
      if (ferror(dest->outfile))
        ERREXIT(cinfo, JERR_FILE_WRITE);
    }

    /*
     * Prepare for output to a stdio stream.
     * The caller must have already opened the stream, and is responsible
     * for closing it after finishing compression.
     */

    GLOBAL(void)
    jpeg_stdio_dest (j_compress_ptr cinfo, FILE * outfile)
    {
      my_dest_ptr dest;

      /* The destination object is made permanent so that multiple JPEG images
       * can be written to the same file without re-executing jpeg_stdio_dest.
       * This makes it dangerous to use this manager and a different destination
       * manager serially with the same JPEG object, because their private object
       * sizes may be different.  Caveat programmer.
       */
      if (cinfo->dest == NULL) {	/* first time for this JPEG object? */
        cinfo->dest = (struct jpeg_destination_mgr *)
          (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
    				  SIZEOF(my_destination_mgr));
      }

      dest = (my_dest_ptr) cinfo->dest;
      dest->pub.init_destination = init_destination;
      dest->pub.empty_output_buffer = empty_output_buffer;
      dest->pub.term_destination = term_destination;
      dest->outfile = outfile;
    }