src/jpeg/jdatadst.c

   1 /*
   2  * jdatadst.c
   3  *
   4  * Copyright (C) 1994-1996, Thomas G. Lane.
   5  * This file is part of the Independent JPEG Group's software.
   6  * For conditions of distribution and use, see the accompanying README file.
   7  *
   8  * This file contains compression data destination routines for the case of
   9  * emitting JPEG data to a file (or any stdio stream).  While these routines
  10  * are sufficient for most applications, some will want to use a different
  11  * destination manager.
  12  * IMPORTANT: we assume that fwrite() will correctly transcribe an array of
  13  * JOCTETs into 8-bit-wide elements on external storage.  If char is wider
  14  * than 8 bits on your machine, you may need to do some tweaking.
  15  */
  16
  17 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
  18 #include "jinclude.h"
  19 #include "jpeglib.h"
  20 #include "jerror.h"
  21
  22
  23 /* Expanded data destination object for stdio output */
  24
  25 typedef struct {
  26   struct jpeg_destination_mgr pub; /* public fields */
  27
  28   FILE * outfile;               /* target stream */
  29   JOCTET * buffer;              /* start of buffer */
  30 } my_destination_mgr;
  31
  32 typedef my_destination_mgr * my_dest_ptr;
  33
  34 #define OUTPUT_BUF_SIZE  4096   /* choose an efficiently fwrite'able size */
  35
  36
  37 /*
  38  * Initialize destination --- called by jpeg_start_compress
  39  * before any data is actually written.
  40  */
  41
  42 METHODDEF(void)
  43 init_destination (j_compress_ptr cinfo)
  44 {
  45   my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
  46
  47   /* Allocate the output buffer --- it will be released when done with image */
  48   dest->buffer = (JOCTET *)
  49       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  50                                   OUTPUT_BUF_SIZE * SIZEOF(JOCTET));
  51
  52   dest->pub.next_output_byte = dest->buffer;
  53   dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
  54 }
  55
  56
  57 /*
  58  * Empty the output buffer --- called whenever buffer fills up.
  59  *
  60  * In typical applications, this should write the entire output buffer
  61  * (ignoring the current state of next_output_byte & free_in_buffer),
  62  * reset the pointer & count to the start of the buffer, and return TRUE
  63  * indicating that the buffer has been dumped.
  64  *
  65  * In applications that need to be able to suspend compression due to output
  66  * overrun, a FALSE return indicates that the buffer cannot be emptied now.
  67  * In this situation, the compressor will return to its caller (possibly with
  68  * an indication that it has not accepted all the supplied scanlines).  The
  69  * application should resume compression after it has made more room in the
  70  * output buffer.  Note that there are substantial restrictions on the use of
  71  * suspension --- see the documentation.
  72  *
  73  * When suspending, the compressor will back up to a convenient restart point
  74  * (typically the start of the current MCU). next_output_byte & free_in_buffer
  75  * indicate where the restart point will be if the current call returns FALSE.
  76  * Data beyond this point will be regenerated after resumption, so do not
  77  * write it out when emptying the buffer externally.
  78  */
  79
  80 METHODDEF(wxjpeg_boolean)
  81 empty_output_buffer (j_compress_ptr cinfo)
  82 {
  83   my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
  84
  85   if (JFWRITE(dest->outfile, dest->buffer, OUTPUT_BUF_SIZE) !=
  86       (size_t) OUTPUT_BUF_SIZE)
  87     ERREXIT(cinfo, JERR_FILE_WRITE);
  88
  89   dest->pub.next_output_byte = dest->buffer;
  90   dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
  91
  92   return TRUE;
  93 }
  94
  95
  96 /*
  97  * Terminate destination --- called by jpeg_finish_compress
  98  * after all data has been written.  Usually needs to flush buffer.
  99  *
 100  * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
 101  * application must deal with any cleanup that should happen even
 102  * for error exit.
 103  */
 104
 105 METHODDEF(void)
 106 term_destination (j_compress_ptr cinfo)
 107 {
 108   my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
 109   size_t datacount = OUTPUT_BUF_SIZE - dest->pub.free_in_buffer;
 110
 111   /* Write any data remaining in the buffer */
 112   if (datacount > 0) {
 113     if (JFWRITE(dest->outfile, dest->buffer, datacount) != datacount)
 114       ERREXIT(cinfo, JERR_FILE_WRITE);
 115   }
 116   fflush(dest->outfile);
 117   /* Make sure we wrote the output file OK */
 118   if (ferror(dest->outfile))
 119     ERREXIT(cinfo, JERR_FILE_WRITE);
 120 }
 121
 122
 123 /*
 124  * Prepare for output to a stdio stream.
 125  * The caller must have already opened the stream, and is responsible
 126  * for closing it after finishing compression.
 127  */
 128
 129 GLOBAL(void)
 130 jpeg_stdio_dest (j_compress_ptr cinfo, FILE * outfile)
 131 {
 132   my_dest_ptr dest;
 133
 134   /* The destination object is made permanent so that multiple JPEG images
 135    * can be written to the same file without re-executing jpeg_stdio_dest.
 136    * This makes it dangerous to use this manager and a different destination
 137    * manager serially with the same JPEG object, because their private object
 138    * sizes may be different.  Caveat programmer.
 139    */
 140   if (cinfo->dest == NULL) {    /* first time for this JPEG object? */
 141     cinfo->dest = (struct jpeg_destination_mgr *)
 142       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
 143                                   SIZEOF(my_destination_mgr));
 144   }
 145
 146   dest = (my_dest_ptr) cinfo->dest;
 147   dest->pub.init_destination = init_destination;
 148   dest->pub.empty_output_buffer = empty_output_buffer;
 149   dest->pub.term_destination = term_destination;
 150   dest->outfile = outfile;
 151 }