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 */
19 /* Expanded data source object for stdio input */
22 typedef int(*int_jpeg_decompress_struct)(jpeg_decompress_struct*);
23 typedef void(*void_jpeg_decompress_struct)(jpeg_decompress_struct*);
24 typedef void(*void_jpeg_decompress_struct_long)(jpeg_decompress_struct*,long);
28 struct jpeg_source_mgr pub; /* public fields */
30 std::ifstream *infile; /* source stream */
31 JOCTET * buffer; /* start of buffer */
32 boolean start_of_file; /* have we gotten any data yet? */
34 gdcm::JPEGFragment *frag;
38 typedef my_source_mgr * my_src_ptr;
40 #define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
44 * Initialize source --- called by jpeg_read_header
45 * before any data is actually read.
49 init_source (j_decompress_ptr cinfo)
51 my_src_ptr src = (my_src_ptr) cinfo->src;
53 /* We reset the empty-input-file flag for each image,
54 * but we don't clear the input buffer.
55 * This is correct behavior for reading a series of images from one source.
57 src->start_of_file = TRUE;
62 * Fill the input buffer --- called whenever buffer is emptied.
64 * In typical applications, this should read fresh data into the buffer
65 * (ignoring the current state of next_input_byte & bytes_in_buffer),
66 * reset the pointer & count to the start of the buffer, and return TRUE
67 * indicating that the buffer has been reloaded. It is not necessary to
68 * fill the buffer entirely, only to obtain at least one more byte.
70 * There is no such thing as an EOF return. If the end of the file has been
71 * reached, the routine has a choice of ERREXIT() or inserting fake data into
72 * the buffer. In most cases, generating a warning message and inserting a
73 * fake EOI marker is the best course of action --- this will allow the
74 * decompressor to output however much of the image is there. However,
75 * the resulting error message is misleading if the real problem is an empty
76 * input file, so we handle that case specially.
78 * In applications that need to be able to suspend compression due to input
79 * not being available yet, a FALSE return indicates that no more data can be
80 * obtained right now, but more may be forthcoming later. In this situation,
81 * the decompressor will return to its caller (with an indication of the
82 * number of scanlines it has read, if any). The application should resume
83 * decompression after it has loaded more data into the input buffer. Note
84 * that there are substantial restrictions on the use of suspension --- see
87 * When suspending, the decompressor will back up to a convenient restart point
88 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
89 * indicate where the restart point will be if the current call returns FALSE.
90 * Data beyond this point must be rescanned after resumption, so move it to
91 * the front of the buffer rather than discarding it.
95 fill_input_buffer (j_decompress_ptr cinfo)
97 my_src_ptr src = (my_src_ptr) cinfo->src;
99 if( src->bytes_read == src->frag->GetLength() )
101 // Start the I/O suspension simply by returning false here:
105 size_t input_buf_size = INPUT_BUF_SIZE;
106 if( (src->bytes_read + INPUT_BUF_SIZE) > src->frag->GetLength() )
108 input_buf_size = src->frag->GetLength() - src->bytes_read;
111 src->infile->read( (char*)src->buffer, input_buf_size);
112 size_t nbytes = src->infile->gcount();
115 if (src->start_of_file) /* Treat empty input file as fatal error */
116 ERREXIT(cinfo, JERR_INPUT_EMPTY);
117 WARNMS(cinfo, JWRN_JPEG_EOF);
118 /* Insert a fake EOI marker */
119 src->buffer[0] = (JOCTET) 0xFF;
120 src->buffer[1] = (JOCTET) JPEG_EOI;
124 src->pub.next_input_byte = src->buffer;
125 src->pub.bytes_in_buffer = nbytes;
126 src->start_of_file = FALSE;
127 src->bytes_read += nbytes;
134 * Skip data --- used to skip over a potentially large amount of
135 * uninteresting data (such as an APPn marker).
137 * Writers of suspendable-input applications must note that skip_input_data
138 * is not granted the right to give a suspension return. If the skip extends
139 * beyond the data currently in the buffer, the buffer can be marked empty so
140 * that the next read will cause a fill_input_buffer call that can suspend.
141 * Arranging for additional bytes to be discarded before reloading the input
142 * buffer is the application writer's problem.
146 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
148 my_src_ptr src = (my_src_ptr) cinfo->src;
150 /* Just a dumb implementation for now. Could use fseek() except
151 * it doesn't work on pipes. Not clear that being smart is worth
152 * any trouble anyway --- large skips are infrequent.
155 while (num_bytes > (long) src->pub.bytes_in_buffer) {
156 num_bytes -= (long) src->pub.bytes_in_buffer;
157 (void) fill_input_buffer(cinfo);
158 /* note we assume that fill_input_buffer will never return FALSE,
159 * so suspension need not be handled.
162 src->pub.next_input_byte += (size_t) num_bytes;
163 src->pub.bytes_in_buffer -= (size_t) num_bytes;
169 * An additional method that can be provided by data source modules is the
170 * resync_to_restart method for error recovery in the presence of RST markers.
171 * For the moment, this source module just uses the default resync method
172 * provided by the JPEG library. That method assumes that no backtracking
178 * Terminate source --- called by jpeg_finish_decompress
179 * after all data has been read. Often a no-op.
181 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
182 * application must deal with any cleanup that should happen even
187 term_source (j_decompress_ptr cinfo)
190 /* no work necessary here */
195 * Prepare for input from a stdio stream.
196 * The caller must have already opened the stream, and is responsible
197 * for closing it after finishing decompression.
201 jpeg_stdio_src (j_decompress_ptr cinfo, std::ifstream * infile, gdcm::JPEGFragment *frag, int flag)
205 /* The source object and input buffer are made permanent so that a series
206 * of JPEG images can be read from the same file by calling jpeg_stdio_src
207 * only before the first one. (If we discarded the buffer at the end of
208 * one image, we'd likely lose the start of the next one.)
209 * This makes it unsafe to use this manager and a different source
210 * manager serially with the same JPEG object. Caveat programmer.
212 if (cinfo->src == NULL) { /* first time for this JPEG object? */
213 cinfo->src = (struct jpeg_source_mgr *)
214 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
215 SIZEOF(my_source_mgr));
216 src = (my_src_ptr) cinfo->src;
217 src->buffer = (JOCTET *)
218 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
219 INPUT_BUF_SIZE * SIZEOF(JOCTET));
222 src = (my_src_ptr) cinfo->src;
223 src->pub.init_source = reinterpret_cast<void_jpeg_decompress_struct>(init_source);
224 src->pub.fill_input_buffer = reinterpret_cast<int_jpeg_decompress_struct>(fill_input_buffer);
225 src->pub.skip_input_data = reinterpret_cast<void_jpeg_decompress_struct_long>(skip_input_data);
226 src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
227 src->pub.term_source = reinterpret_cast<void_jpeg_decompress_struct>(term_source);
228 src->infile = infile;
230 // Need to setup a new buffer, clean bytes_in_buffer and next_input_byte
233 src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
234 src->pub.next_input_byte = NULL; /* until buffer loaded */
236 //only upate the new fragment, valid for both 'flag' value