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.
8 * This file contains decompression data source routines for the case of
9 * reading JPEG data from a file (or any stdio stream). While these routines
10 * are sufficient for most applications, some will want to use a different
12 * IMPORTANT: we assume that fread() will correctly transcribe an array of
13 * JOCTETs from 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.
17 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
18 #include <gdcmjpeg/jinclude.h>
19 #include <gdcmjpeg/jerror.h>
21 /* Expanded data source object for stdio input */
24 struct jpeg_source_mgr pub; /* public fields */
26 std::ifstream *infile; /* source stream */
27 JOCTET * buffer; /* start of buffer */
28 boolean start_of_file; /* have we gotten any data yet? */
31 typedef my_source_mgr * my_src_ptr;
33 #define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
37 * Initialize source --- called by jpeg_read_header
38 * before any data is actually read.
42 init_source (j_decompress_ptr cinfo)
44 my_src_ptr src = (my_src_ptr) cinfo->src;
46 /* We reset the empty-input-file flag for each image,
47 * but we don't clear the input buffer.
48 * This is correct behavior for reading a series of images from one source.
50 src->start_of_file = TRUE;
55 * Fill the input buffer --- called whenever buffer is emptied.
57 * In typical applications, this should read fresh data into the buffer
58 * (ignoring the current state of next_input_byte & bytes_in_buffer),
59 * reset the pointer & count to the start of the buffer, and return TRUE
60 * indicating that the buffer has been reloaded. It is not necessary to
61 * fill the buffer entirely, only to obtain at least one more byte.
63 * There is no such thing as an EOF return. If the end of the file has been
64 * reached, the routine has a choice of ERREXIT() or inserting fake data into
65 * the buffer. In most cases, generating a warning message and inserting a
66 * fake EOI marker is the best course of action --- this will allow the
67 * decompressor to output however much of the image is there. However,
68 * the resulting error message is misleading if the real problem is an empty
69 * input file, so we handle that case specially.
71 * In applications that need to be able to suspend compression due to input
72 * not being available yet, a FALSE return indicates that no more data can be
73 * obtained right now, but more may be forthcoming later. In this situation,
74 * the decompressor will return to its caller (with an indication of the
75 * number of scanlines it has read, if any). The application should resume
76 * decompression after it has loaded more data into the input buffer. Note
77 * that there are substantial restrictions on the use of suspension --- see
80 * When suspending, the decompressor will back up to a convenient restart point
81 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
82 * indicate where the restart point will be if the current call returns FALSE.
83 * Data beyond this point must be rescanned after resumption, so move it to
84 * the front of the buffer rather than discarding it.
88 fill_input_buffer (j_decompress_ptr cinfo)
90 my_src_ptr src = (my_src_ptr) cinfo->src;
92 src->infile->read( (char*)src->buffer, INPUT_BUF_SIZE);
93 size_t nbytes = src->infile->gcount();
96 if (src->start_of_file) /* Treat empty input file as fatal error */
97 ERREXIT(cinfo, JERR_INPUT_EMPTY);
98 WARNMS(cinfo, JWRN_JPEG_EOF);
99 /* Insert a fake EOI marker */
100 src->buffer[0] = (JOCTET) 0xFF;
101 src->buffer[1] = (JOCTET) JPEG_EOI;
105 src->pub.next_input_byte = src->buffer;
106 src->pub.bytes_in_buffer = nbytes;
107 src->start_of_file = FALSE;
114 * Skip data --- used to skip over a potentially large amount of
115 * uninteresting data (such as an APPn marker).
117 * Writers of suspendable-input applications must note that skip_input_data
118 * is not granted the right to give a suspension return. If the skip extends
119 * beyond the data currently in the buffer, the buffer can be marked empty so
120 * that the next read will cause a fill_input_buffer call that can suspend.
121 * Arranging for additional bytes to be discarded before reloading the input
122 * buffer is the application writer's problem.
126 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
128 my_src_ptr src = (my_src_ptr) cinfo->src;
130 /* Just a dumb implementation for now. Could use fseek() except
131 * it doesn't work on pipes. Not clear that being smart is worth
132 * any trouble anyway --- large skips are infrequent.
135 while (num_bytes > (long) src->pub.bytes_in_buffer) {
136 num_bytes -= (long) src->pub.bytes_in_buffer;
137 (void) fill_input_buffer(cinfo);
138 /* note we assume that fill_input_buffer will never return FALSE,
139 * so suspension need not be handled.
142 src->pub.next_input_byte += (size_t) num_bytes;
143 src->pub.bytes_in_buffer -= (size_t) num_bytes;
149 * An additional method that can be provided by data source modules is the
150 * resync_to_restart method for error recovery in the presence of RST markers.
151 * For the moment, this source module just uses the default resync method
152 * provided by the JPEG library. That method assumes that no backtracking
158 * Terminate source --- called by jpeg_finish_decompress
159 * after all data has been read. Often a no-op.
161 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
162 * application must deal with any cleanup that should happen even
167 term_source (j_decompress_ptr cinfo)
170 /* no work necessary here */
175 * Prepare for input from a stdio stream.
176 * The caller must have already opened the stream, and is responsible
177 * for closing it after finishing decompression.
181 jpeg_stdio_src (j_decompress_ptr cinfo, std::ifstream * infile)
185 /* The source object and input buffer are made permanent so that a series
186 * of JPEG images can be read from the same file by calling jpeg_stdio_src
187 * only before the first one. (If we discarded the buffer at the end of
188 * one image, we'd likely lose the start of the next one.)
189 * This makes it unsafe to use this manager and a different source
190 * manager serially with the same JPEG object. Caveat programmer.
192 if (cinfo->src == NULL) { /* first time for this JPEG object? */
193 cinfo->src = (struct jpeg_source_mgr *)
194 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
195 SIZEOF(my_source_mgr));
196 src = (my_src_ptr) cinfo->src;
197 src->buffer = (JOCTET *)
198 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
199 INPUT_BUF_SIZE * SIZEOF(JOCTET));
202 src = (my_src_ptr) cinfo->src;
203 src->pub.init_source = init_source;
204 src->pub.fill_input_buffer = fill_input_buffer;
205 src->pub.skip_input_data = skip_input_data;
206 src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
207 src->pub.term_source = term_source;
208 src->infile = infile;
209 src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
210 src->pub.next_input_byte = NULL; /* until buffer loaded */