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)
init_destination(j_compress_ptr cinfo)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)
empty_output_buffer(j_compress_ptr cinfo)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)
term_destination(j_compress_ptr cinfo)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)
jpeg_stdio_dest(j_compress_ptr cinfo,FILE * outfile)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