source: liacs/MIR2010/SourceCode/cximage/jpeg/jdatadst.c@ 422

/*

 * 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(boolean)

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;

}