www.pudn.com > imgport.rar > jdatadst.c, change:2008-11-05,size:5270b


/* 
 * 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; 
}