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      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(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 }
    152