Visualization Library 2.0.0-b5

A lightweight C++ OpenGL middleware for 2D/3D graphics

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jdatasrc.c
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1 /*
2  * jdatasrc.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 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
11  * source manager.
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.
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 source object for stdio input */
24 
25 typedef struct {
26  struct jpeg_source_mgr pub; /* public fields */
27 
28  FILE * infile; /* source stream */
29  JOCTET * buffer; /* start of buffer */
30  boolean start_of_file; /* have we gotten any data yet? */
31 } my_source_mgr;
32 
33 typedef my_source_mgr * my_src_ptr;
34 
35 #define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
36 
37 
38 /*
39  * Initialize source --- called by jpeg_read_header
40  * before any data is actually read.
41  */
42 
43 METHODDEF(void)
45 {
46  my_src_ptr src = (my_src_ptr) cinfo->src;
47 
48  /* We reset the empty-input-file flag for each image,
49  * but we don't clear the input buffer.
50  * This is correct behavior for reading a series of images from one source.
51  */
52  src->start_of_file = TRUE;
53 }
54 
55 
56 /*
57  * Fill the input buffer --- called whenever buffer is emptied.
58  *
59  * In typical applications, this should read fresh data into the buffer
60  * (ignoring the current state of next_input_byte & bytes_in_buffer),
61  * reset the pointer & count to the start of the buffer, and return TRUE
62  * indicating that the buffer has been reloaded. It is not necessary to
63  * fill the buffer entirely, only to obtain at least one more byte.
64  *
65  * There is no such thing as an EOF return. If the end of the file has been
66  * reached, the routine has a choice of ERREXIT() or inserting fake data into
67  * the buffer. In most cases, generating a warning message and inserting a
68  * fake EOI marker is the best course of action --- this will allow the
69  * decompressor to output however much of the image is there. However,
70  * the resulting error message is misleading if the real problem is an empty
71  * input file, so we handle that case specially.
72  *
73  * In applications that need to be able to suspend compression due to input
74  * not being available yet, a FALSE return indicates that no more data can be
75  * obtained right now, but more may be forthcoming later. In this situation,
76  * the decompressor will return to its caller (with an indication of the
77  * number of scanlines it has read, if any). The application should resume
78  * decompression after it has loaded more data into the input buffer. Note
79  * that there are substantial restrictions on the use of suspension --- see
80  * the documentation.
81  *
82  * When suspending, the decompressor will back up to a convenient restart point
83  * (typically the start of the current MCU). next_input_byte & bytes_in_buffer
84  * indicate where the restart point will be if the current call returns FALSE.
85  * Data beyond this point must be rescanned after resumption, so move it to
86  * the front of the buffer rather than discarding it.
87  */
88 
89 METHODDEF(boolean)
91 {
92  my_src_ptr src = (my_src_ptr) cinfo->src;
93  size_t nbytes;
94 
95  nbytes = JFREAD(src->infile, src->buffer, INPUT_BUF_SIZE);
96 
97  if (nbytes <= 0) {
98  if (src->start_of_file) /* Treat empty input file as fatal error */
99  ERREXIT(cinfo, JERR_INPUT_EMPTY);
100  WARNMS(cinfo, JWRN_JPEG_EOF);
101  /* Insert a fake EOI marker */
102  src->buffer[0] = (JOCTET) 0xFF;
103  src->buffer[1] = (JOCTET) JPEG_EOI;
104  nbytes = 2;
105  }
106 
107  src->pub.next_input_byte = src->buffer;
108  src->pub.bytes_in_buffer = nbytes;
109  src->start_of_file = FALSE;
110 
111  return TRUE;
112 }
113 
114 
115 /*
116  * Skip data --- used to skip over a potentially large amount of
117  * uninteresting data (such as an APPn marker).
118  *
119  * Writers of suspendable-input applications must note that skip_input_data
120  * is not granted the right to give a suspension return. If the skip extends
121  * beyond the data currently in the buffer, the buffer can be marked empty so
122  * that the next read will cause a fill_input_buffer call that can suspend.
123  * Arranging for additional bytes to be discarded before reloading the input
124  * buffer is the application writer's problem.
125  */
126 
127 METHODDEF(void)
129 {
130  my_src_ptr src = (my_src_ptr) cinfo->src;
131 
132  /* Just a dumb implementation for now. Could use fseek() except
133  * it doesn't work on pipes. Not clear that being smart is worth
134  * any trouble anyway --- large skips are infrequent.
135  */
136  if (num_bytes > 0) {
137  while (num_bytes > (long) src->pub.bytes_in_buffer) {
138  num_bytes -= (long) src->pub.bytes_in_buffer;
139  (void) fill_input_buffer(cinfo);
140  /* note we assume that fill_input_buffer will never return FALSE,
141  * so suspension need not be handled.
142  */
143  }
144  src->pub.next_input_byte += (size_t) num_bytes;
145  src->pub.bytes_in_buffer -= (size_t) num_bytes;
146  }
147 }
148 
149 
150 /*
151  * An additional method that can be provided by data source modules is the
152  * resync_to_restart method for error recovery in the presence of RST markers.
153  * For the moment, this source module just uses the default resync method
154  * provided by the JPEG library. That method assumes that no backtracking
155  * is possible.
156  */
157 
158 
159 /*
160  * Terminate source --- called by jpeg_finish_decompress
161  * after all data has been read. Often a no-op.
162  *
163  * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
164  * application must deal with any cleanup that should happen even
165  * for error exit.
166  */
167 
168 METHODDEF(void)
170 {
171  /* no work necessary here */
172 }
173 
174 
175 /*
176  * Prepare for input from a stdio stream.
177  * The caller must have already opened the stream, and is responsible
178  * for closing it after finishing decompression.
179  */
180 
181 GLOBAL(void)
183 {
184  my_src_ptr src;
185 
186  /* The source object and input buffer are made permanent so that a series
187  * of JPEG images can be read from the same file by calling jpeg_stdio_src
188  * only before the first one. (If we discarded the buffer at the end of
189  * one image, we'd likely lose the start of the next one.)
190  * This makes it unsafe to use this manager and a different source
191  * manager serially with the same JPEG object. Caveat programmer.
192  */
193  if (cinfo->src == NULL) { /* first time for this JPEG object? */
194  cinfo->src = (struct jpeg_source_mgr *)
195  (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
196  SIZEOF(my_source_mgr));
197  src = (my_src_ptr) cinfo->src;
198  src->buffer = (JOCTET *)
199  (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
201  }
202 
203  src = (my_src_ptr) cinfo->src;
204  src->pub.init_source = init_source;
205  src->pub.fill_input_buffer = fill_input_buffer;
206  src->pub.skip_input_data = skip_input_data;
207  src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
208  src->pub.term_source = term_source;
209  src->infile = infile;
210  src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
211  src->pub.next_input_byte = NULL; /* until buffer loaded */
212 }
term_source(j_decompress_ptr cinfo)
Definition: jdatasrc.c:169
#define NULL
Definition: ftobjs.h:61
struct jpeg_common_struct * j_common_ptr
Definition: jpeglib.h:261
#define ERREXIT(cinfo, code)
Definition: jerror.h:205
#define SIZEOF(object)
Definition: jinclude.h:80
#define JFREAD(file, buf, sizeofbuf)
Definition: jinclude.h:88
int num_bytes
Definition: png.h:1360
init_source(j_decompress_ptr cinfo)
Definition: jdatasrc.c:44
#define INPUT_BUF_SIZE
Definition: jdatasrc.c:35
jpeg_stdio_src(j_decompress_ptr cinfo, FILE *infile)
Definition: jdatasrc.c:182
typedef long(ZCALLBACK *tell_file_func) OF((voidpf opaque
GLuint buffer
GLenum src
#define WARNMS(cinfo, code)
Definition: jerror.h:238
#define FALSE
Definition: ftobjs.h:57
skip_input_data(j_decompress_ptr cinfo, long num_bytes)
Definition: jdatasrc.c:128
jpeg_resync_to_restart(j_decompress_ptr cinfo, int desired)
Definition: jdmarker.c:1192
if(!abbox) return FT_THROW(Invalid_Argument)
#define GLOBAL(type)
Definition: jmorecfg.h:191
#define METHODDEF(type)
Definition: jmorecfg.h:187
FILE * infile
Definition: cdjpeg.h:141
#define JPEG_EOI
Definition: jpeglib.h:1046
my_source_mgr * my_src_ptr
Definition: jdatasrc.c:33
#define JPOOL_PERMANENT
Definition: jpeglib.h:748
char JOCTET
Definition: jmorecfg.h:115
fill_input_buffer(j_decompress_ptr cinfo)
Definition: jdatasrc.c:90
#define TRUE
Definition: ftobjs.h:53