/* * 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;}