source: golgotha/src/i4/loaders/jpg/jdatasrc.cc @ 80

Last change on this file since 80 was 80, checked in by Sam Hocevar, 12 years ago
  • Adding the Golgotha source code. Not sure what's going to be interesting in there, but since it's all public domain, there's certainly stuff to pick up.
File size: 8.2 KB
Line 
1/********************************************************************** <BR>
2  This file is part of Crack dot Com's free source code release of
3  Golgotha. <a href="http://www.crack.com/golgotha_release"> <BR> for
4  information about compiling & licensing issues visit this URL</a>
5  <PRE> If that doesn't help, contact Jonathan Clark at
6  golgotha_source@usa.net (Subject should have "GOLG" in it)
7***********************************************************************/
8
9/*
10 * jdatasrc.c
11 *
12 * Copyright (C) 1994-1996, Thomas G. Lane.
13 * This file is part of the Independent JPEG Group's software.
14 * For conditions of distribution and use, see the accompanying README file.
15 *
16 * This file contains decompression data source routines for the case of
17 * reading JPEG data from a file (or any stdio stream).  While these routines
18 * are sufficient for most applications, some will want to use a different
19 * source manager.
20 * IMPORTANT: we assume that fread() will correctly transcribe an array of
21 * JOCTETs from 8-bit-wide elements on external storage.  If char is wider
22 * than 8 bits on your machine, you may need to do some tweaking.
23 */
24
25/* this is not a core library module, so it doesn't define JPEG_INTERNALS */
26#include "loaders/jpg/jinclude.h"
27#include "loaders/jpg/jpeglib.h"
28#include "loaders/jpg/jerror.h"
29
30
31/* Expanded data source object for stdio input */
32
33typedef struct {
34  struct jpeg_source_mgr pub;   /* public fields */
35
36  i4_file_class * infile;               /* source stream */
37  JOCTET * buffer;              /* start of buffer */
38  boolean start_of_file;        /* have we gotten any data yet? */
39} my_source_mgr;
40
41typedef my_source_mgr * my_src_ptr;
42
43#define INPUT_BUF_SIZE  4096    /* choose an efficiently fread'able size */
44
45
46/*
47 * Initialize source --- called by jpeg_read_header
48 * before any data is actually read.
49 */
50
51METHODDEF(void)
52init_source (j_decompress_ptr cinfo)
53{
54  my_src_ptr src = (my_src_ptr) cinfo->src;
55
56  /* We reset the empty-input-file flag for each image,
57   * but we don't clear the input buffer.
58   * This is correct behavior for reading a series of images from one source.
59   */
60  src->start_of_file = TRUE;
61}
62
63
64/*
65 * Fill the input buffer --- called whenever buffer is emptied.
66 *
67 * In typical applications, this should read fresh data into the buffer
68 * (ignoring the current state of next_input_byte & bytes_in_buffer),
69 * reset the pointer & count to the start of the buffer, and return TRUE
70 * indicating that the buffer has been reloaded.  It is not necessary to
71 * fill the buffer entirely, only to obtain at least one more byte.
72 *
73 * There is no such thing as an EOF return.  If the end of the file has been
74 * reached, the routine has a choice of ERREXIT() or inserting fake data into
75 * the buffer.  In most cases, generating a warning message and inserting a
76 * fake EOI marker is the best course of action --- this will allow the
77 * decompressor to output however much of the image is there.  However,
78 * the resulting error message is misleading if the real problem is an empty
79 * input file, so we handle that case specially.
80 *
81 * In applications that need to be able to suspend compression due to input
82 * not being available yet, a FALSE return indicates that no more data can be
83 * obtained right now, but more may be forthcoming later.  In this situation,
84 * the decompressor will return to its caller (with an indication of the
85 * number of scanlines it has read, if any).  The application should resume
86 * decompression after it has loaded more data into the input buffer.  Note
87 * that there are substantial restrictions on the use of suspension --- see
88 * the documentation.
89 *
90 * When suspending, the decompressor will back up to a convenient restart point
91 * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
92 * indicate where the restart point will be if the current call returns FALSE.
93 * Data beyond this point must be rescanned after resumption, so move it to
94 * the front of the buffer rather than discarding it.
95 */
96
97METHODDEF(boolean)
98fill_input_buffer (j_decompress_ptr cinfo)
99{
100  my_src_ptr src = (my_src_ptr) cinfo->src;
101  size_t nbytes;
102
103  nbytes = src->infile->read(src->buffer, INPUT_BUF_SIZE);
104
105  if (nbytes <= 0) {
106    if (src->start_of_file)     /* Treat empty input file as fatal error */
107      ERREXIT(cinfo, JERR_INPUT_EMPTY);
108    WARNMS(cinfo, JWRN_JPEG_EOF);
109    /* Insert a fake EOI marker */
110    src->buffer[0] = (JOCTET) 0xFF;
111    src->buffer[1] = (JOCTET) JPEG_EOI;
112    nbytes = 2;
113  }
114
115  src->pub.next_input_byte = src->buffer;
116  src->pub.bytes_in_buffer = nbytes;
117  src->start_of_file = FALSE;
118
119  return TRUE;
120}
121
122
123/*
124 * Skip data --- used to skip over a potentially large amount of
125 * uninteresting data (such as an APPn marker).
126 *
127 * Writers of suspendable-input applications must note that skip_input_data
128 * is not granted the right to give a suspension return.  If the skip extends
129 * beyond the data currently in the buffer, the buffer can be marked empty so
130 * that the next read will cause a fill_input_buffer call that can suspend.
131 * Arranging for additional bytes to be discarded before reloading the input
132 * buffer is the application writer's problem.
133 */
134
135METHODDEF(void)
136skip_input_data (j_decompress_ptr cinfo, long num_bytes)
137{
138  my_src_ptr src = (my_src_ptr) cinfo->src;
139
140  /* Just a dumb implementation for now.  Could use fseek() except
141   * it doesn't work on pipes.  Not clear that being smart is worth
142   * any trouble anyway --- large skips are infrequent.
143   */
144  if (num_bytes > 0) {
145    while (num_bytes > (long) src->pub.bytes_in_buffer) {
146      num_bytes -= (long) src->pub.bytes_in_buffer;
147      (void) fill_input_buffer(cinfo);
148      /* note we assume that fill_input_buffer will never return FALSE,
149       * so suspension need not be handled.
150       */
151    }
152    src->pub.next_input_byte += (size_t) num_bytes;
153    src->pub.bytes_in_buffer -= (size_t) num_bytes;
154  }
155}
156
157
158/*
159 * An additional method that can be provided by data source modules is the
160 * resync_to_restart method for error recovery in the presence of RST markers.
161 * For the moment, this source module just uses the default resync method
162 * provided by the JPEG library.  That method assumes that no backtracking
163 * is possible.
164 */
165
166
167/*
168 * Terminate source --- called by jpeg_finish_decompress
169 * after all data has been read.  Often a no-op.
170 *
171 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
172 * application must deal with any cleanup that should happen even
173 * for error exit.
174 */
175
176METHODDEF(void)
177term_source (j_decompress_ptr cinfo)
178{
179  /* no work necessary here */
180}
181
182
183/*
184 * Prepare for input from a stdio stream.
185 * The caller must have already opened the stream, and is responsible
186 * for closing it after finishing decompression.
187 */
188
189GLOBAL(void)
190jpeg_stdio_src (j_decompress_ptr cinfo, i4_file_class * infile)
191{
192  my_src_ptr src;
193
194  /* The source object and input buffer are made permanent so that a series
195   * of JPEG images can be read from the same file by calling jpeg_stdio_src
196   * only before the first one.  (If we discarded the buffer at the end of
197   * one image, we'd likely lose the start of the next one.)
198   * This makes it unsafe to use this manager and a different source
199   * manager serially with the same JPEG object.  Caveat programmer.
200   */
201  if (cinfo->src == NULL) {     /* first time for this JPEG object? */
202    cinfo->src = (struct jpeg_source_mgr *)
203      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
204                                  SIZEOF(my_source_mgr));
205    src = (my_src_ptr) cinfo->src;
206    src->buffer = (JOCTET *)
207      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
208                                  INPUT_BUF_SIZE * SIZEOF(JOCTET));
209  }
210
211  src = (my_src_ptr) cinfo->src;
212  src->pub.init_source = init_source;
213  src->pub.fill_input_buffer = fill_input_buffer;
214  src->pub.skip_input_data = skip_input_data;
215  src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
216  src->pub.term_source = term_source;
217  src->infile = infile;
218  src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
219  src->pub.next_input_byte = NULL; /* until buffer loaded */
220}
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