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Member "chandler-1.0.3/external/wx/wxPython-r218/src/jpeg/jdatasrc.c" (15 Dec 2006, 7618 Bytes) of archive /windows/misc/Chandler_src_1.0.3.tar.gz:


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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   wxjpeg_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)
   44 init_source (j_decompress_ptr cinfo)
   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(wxjpeg_boolean)
   90 fill_input_buffer (j_decompress_ptr cinfo)
   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)
  128 skip_input_data (j_decompress_ptr cinfo, long num_bytes)
  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)
  169 term_source (j_decompress_ptr cinfo)
  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)
  182 jpeg_stdio_src (j_decompress_ptr cinfo, FILE * infile)
  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,
  200                   INPUT_BUF_SIZE * SIZEOF(JOCTET));
  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 }