compiler/libjpeg/main/jdatadst.c

   1 /*
   2     $Id$
   3 */
   4
   5 /*
   6  * jdatadst.c
   7  *
   8  * Copyright (C) 1994-1996, Thomas G. Lane.
   9  * This file is part of the Independent JPEG Group's software.
  10  * For conditions of distribution and use, see the accompanying README file.
  11  *
  12  * This file contains compression data destination routines for the case of
  13  * emitting JPEG data to a file (or any stdio stream).  While these routines
  14  * are sufficient for most applications, some will want to use a different
  15  * destination manager.
  16  * IMPORTANT: we assume that fwrite() will correctly transcribe an array of
  17  * JOCTETs into 8-bit-wide elements on external storage.  If char is wider
  18  * than 8 bits on your machine, you may need to do some tweaking.
  19  */
  20
  21 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
  22 #include "jinclude.h"
  23 #include "jpeglib.h"
  24 #include "jerror.h"
  25
  26
  27 /* Expanded data destination object for stdio output */
  28
  29 typedef struct {
  30   struct jpeg_destination_mgr pub; /* public fields */
  31
  32   FILE * outfile;               /* target stream */
  33   JOCTET * buffer;              /* start of buffer */
  34 } my_destination_mgr;
  35
  36 typedef my_destination_mgr * my_dest_ptr;
  37
  38 #define OUTPUT_BUF_SIZE  4096   /* choose an efficiently fwrite'able size */
  39
  40
  41 /*
  42  * Initialize destination --- called by jpeg_start_compress
  43  * before any data is actually written.
  44  */
  45
  46 METHODDEF(void)
  47 init_destination (j_compress_ptr cinfo)
  48 {
  49   my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
  50
  51   /* Allocate the output buffer --- it will be released when done with image */
  52   dest->buffer = (JOCTET *)
  53       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  54                                   OUTPUT_BUF_SIZE * SIZEOF(JOCTET));
  55
  56   dest->pub.next_output_byte = dest->buffer;
  57   dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
  58 }
  59
  60
  61 /*
  62  * Empty the output buffer --- called whenever buffer fills up.
  63  *
  64  * In typical applications, this should write the entire output buffer
  65  * (ignoring the current state of next_output_byte & free_in_buffer),
  66  * reset the pointer & count to the start of the buffer, and return TRUE
  67  * indicating that the buffer has been dumped.
  68  *
  69  * In applications that need to be able to suspend compression due to output
  70  * overrun, a FALSE return indicates that the buffer cannot be emptied now.
  71  * In this situation, the compressor will return to its caller (possibly with
  72  * an indication that it has not accepted all the supplied scanlines).  The
  73  * application should resume compression after it has made more room in the
  74  * output buffer.  Note that there are substantial restrictions on the use of
  75  * suspension --- see the documentation.
  76  *
  77  * When suspending, the compressor will back up to a convenient restart point
  78  * (typically the start of the current MCU). next_output_byte & free_in_buffer
  79  * indicate where the restart point will be if the current call returns FALSE.
  80  * Data beyond this point will be regenerated after resumption, so do not
  81  * write it out when emptying the buffer externally.
  82  */
  83
  84 METHODDEF(boolean)
  85 empty_output_buffer (j_compress_ptr cinfo)
  86 {
  87   my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
  88
  89   if (JFWRITE(dest->outfile, dest->buffer, OUTPUT_BUF_SIZE) !=
  90       (size_t) OUTPUT_BUF_SIZE)
  91     ERREXIT(cinfo, JERR_FILE_WRITE);
  92
  93   dest->pub.next_output_byte = dest->buffer;
  94   dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;
  95
  96   return TRUE;
  97 }
  98
  99
 100 /*
 101  * Terminate destination --- called by jpeg_finish_compress
 102  * after all data has been written.  Usually needs to flush buffer.
 103  *
 104  * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
 105  * application must deal with any cleanup that should happen even
 106  * for error exit.
 107  */
 108
 109 METHODDEF(void)
 110 term_destination (j_compress_ptr cinfo)
 111 {
 112   my_dest_ptr dest = (my_dest_ptr) cinfo->dest;
 113   size_t datacount = OUTPUT_BUF_SIZE - dest->pub.free_in_buffer;
 114
 115   /* Write any data remaining in the buffer */
 116   if (datacount > 0) {
 117     if (JFWRITE(dest->outfile, dest->buffer, datacount) != datacount)
 118       ERREXIT(cinfo, JERR_FILE_WRITE);
 119   }
 120   fflush(dest->outfile);
 121   /* Make sure we wrote the output file OK */
 122   if (ferror(dest->outfile))
 123     ERREXIT(cinfo, JERR_FILE_WRITE);
 124 }
 125
 126
 127 /*
 128  * Prepare for output to a stdio stream.
 129  * The caller must have already opened the stream, and is responsible
 130  * for closing it after finishing compression.
 131  */
 132
 133 JGLOBAL(void)
 134 jpeg_stdio_dest (j_compress_ptr cinfo, FILE * outfile)
 135 {
 136   my_dest_ptr dest;
 137
 138   /* The destination object is made permanent so that multiple JPEG images
 139    * can be written to the same file without re-executing jpeg_stdio_dest.
 140    * This makes it dangerous to use this manager and a different destination
 141    * manager serially with the same JPEG object, because their private object
 142    * sizes may be different.  Caveat programmer.
 143    */
 144   if (cinfo->dest == NULL) {    /* first time for this JPEG object? */
 145     cinfo->dest = (struct jpeg_destination_mgr *)
 146       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
 147                                   SIZEOF(my_destination_mgr));
 148   }
 149
 150   dest = (my_dest_ptr) cinfo->dest;
 151   dest->pub.init_destination = init_destination;
 152   dest->pub.empty_output_buffer = empty_output_buffer;
 153   dest->pub.term_destination = term_destination;
 154   dest->outfile = outfile;
 155 }