rdgif.c

Jpeg source code,jpeg编码解码示范

      sinfo->code_size++;
      sinfo->limit_code <<= 1;	/* keep equal to 2^code_size */
    }
  }
  
  sinfo->oldcode = incode;	/* save last input symbol for future use */
  return sinfo->firstcode;	/* return first byte of symbol's expansion */
}


LOCAL(void)
ReadColorMap (gif_source_ptr sinfo, int cmaplen, JSAMPARRAY cmap)
/* Read a GIF colormap */
{
  int i;

  for (i = 0; i < cmaplen; i++) {
#if BITS_IN_JSAMPLE == 8
#define UPSCALE(x)  (x)
#else
#define UPSCALE(x)  ((x) << (BITS_IN_JSAMPLE-8))
#endif
    cmap[CM_RED][i]   = (JSAMPLE) UPSCALE(ReadByte(sinfo));
    cmap[CM_GREEN][i] = (JSAMPLE) UPSCALE(ReadByte(sinfo));
    cmap[CM_BLUE][i]  = (JSAMPLE) UPSCALE(ReadByte(sinfo));
  }
}


LOCAL(void)
DoExtension (gif_source_ptr sinfo)
/* Process an extension block */
/* Currently we ignore 'em all */
{
  int extlabel;

  /* Read extension label byte */
  extlabel = ReadByte(sinfo);
  TRACEMS1(sinfo->cinfo, 1, JTRC_GIF_EXTENSION, extlabel);
  /* Skip the data block(s) associated with the extension */
  SkipDataBlocks(sinfo);
}


/*
 * Read the file header; return image size and component count.
 */

METHODDEF(void)
start_input_gif (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)
{
  gif_source_ptr source = (gif_source_ptr) sinfo;
  char hdrbuf[10];		/* workspace for reading control blocks */
  unsigned int width, height;	/* image dimensions */
  int colormaplen, aspectRatio;
  int c;

  /* Allocate space to store the colormap */
  source->colormap = (*cinfo->mem->alloc_sarray)
    ((j_common_ptr) cinfo, JPOOL_IMAGE,
     (JDIMENSION) MAXCOLORMAPSIZE, (JDIMENSION) NUMCOLORS);

  /* Read and verify GIF Header */
  if (! ReadOK(source->pub.input_file, hdrbuf, 6))
    ERREXIT(cinfo, JERR_GIF_NOT);
  if (hdrbuf[0] != 'G' || hdrbuf[1] != 'I' || hdrbuf[2] != 'F')
    ERREXIT(cinfo, JERR_GIF_NOT);
  /* Check for expected version numbers.
   * If unknown version, give warning and try to process anyway;
   * this is per recommendation in GIF89a standard.
   */
  if ((hdrbuf[3] != '8' || hdrbuf[4] != '7' || hdrbuf[5] != 'a') &&
      (hdrbuf[3] != '8' || hdrbuf[4] != '9' || hdrbuf[5] != 'a'))
    TRACEMS3(cinfo, 1, JTRC_GIF_BADVERSION, hdrbuf[3], hdrbuf[4], hdrbuf[5]);

  /* Read and decipher Logical Screen Descriptor */
  if (! ReadOK(source->pub.input_file, hdrbuf, 7))
    ERREXIT(cinfo, JERR_INPUT_EOF);
  width = LM_to_uint(hdrbuf[0],hdrbuf[1]);
  height = LM_to_uint(hdrbuf[2],hdrbuf[3]);
  colormaplen = 2 << (hdrbuf[4] & 0x07);
  /* we ignore the color resolution, sort flag, and background color index */
  aspectRatio = hdrbuf[6] & 0xFF;
  if (aspectRatio != 0 && aspectRatio != 49)
    TRACEMS(cinfo, 1, JTRC_GIF_NONSQUARE);

  /* Read global colormap if header indicates it is present */
  if (BitSet(hdrbuf[4], COLORMAPFLAG))
    ReadColorMap(source, colormaplen, source->colormap);

  /* Scan until we reach start of desired image.
   * We don't currently support skipping images, but could add it easily.
   */
  for (;;) {
    c = ReadByte(source);

    if (c == ';')		/* GIF terminator?? */
      ERREXIT(cinfo, JERR_GIF_IMAGENOTFOUND);

    if (c == '!') {		/* Extension */
      DoExtension(source);
      continue;
    }
    
    if (c != ',') {		/* Not an image separator? */
      WARNMS1(cinfo, JWRN_GIF_CHAR, c);
      continue;
    }

    /* Read and decipher Local Image Descriptor */
    if (! ReadOK(source->pub.input_file, hdrbuf, 9))
      ERREXIT(cinfo, JERR_INPUT_EOF);
    /* we ignore top/left position info, also sort flag */
    width = LM_to_uint(hdrbuf[4],hdrbuf[5]);
    height = LM_to_uint(hdrbuf[6],hdrbuf[7]);
    source->is_interlaced = BitSet(hdrbuf[8], INTERLACE);

    /* Read local colormap if header indicates it is present */
    /* Note: if we wanted to support skipping images, */
    /* we'd need to skip rather than read colormap for ignored images */
    if (BitSet(hdrbuf[8], COLORMAPFLAG)) {
      colormaplen = 2 << (hdrbuf[8] & 0x07);
      ReadColorMap(source, colormaplen, source->colormap);
    }

    source->input_code_size = ReadByte(source); /* get min-code-size byte */
    if (source->input_code_size < 2 || source->input_code_size >= MAX_LZW_BITS)
      ERREXIT1(cinfo, JERR_GIF_CODESIZE, source->input_code_size);

    /* Reached desired image, so break out of loop */
    /* If we wanted to skip this image, */
    /* we'd call SkipDataBlocks and then continue the loop */
    break;
  }

  /* Prepare to read selected image: first initialize LZW decompressor */
  source->symbol_head = (UINT16 FAR *)
    (*cinfo->mem->alloc_large) ((j_common_ptr) cinfo, JPOOL_IMAGE,
				LZW_TABLE_SIZE * SIZEOF(UINT16));
  source->symbol_tail = (UINT8 FAR *)
    (*cinfo->mem->alloc_large) ((j_common_ptr) cinfo, JPOOL_IMAGE,
				LZW_TABLE_SIZE * SIZEOF(UINT8));
  source->symbol_stack = (UINT8 FAR *)
    (*cinfo->mem->alloc_large) ((j_common_ptr) cinfo, JPOOL_IMAGE,
				LZW_TABLE_SIZE * SIZEOF(UINT8));
  InitLZWCode(source);

  /*
   * If image is interlaced, we read it into a full-size sample array,
   * decompressing as we go; then get_interlaced_row selects rows from the
   * sample array in the proper order.
   */
  if (source->is_interlaced) {
    /* We request the virtual array now, but can't access it until virtual
     * arrays have been allocated.  Hence, the actual work of reading the
     * image is postponed until the first call to get_pixel_rows.
     */
    source->interlaced_image = (*cinfo->mem->request_virt_sarray)
      ((j_common_ptr) cinfo, JPOOL_IMAGE, FALSE,
       (JDIMENSION) width, (JDIMENSION) height, (JDIMENSION) 1);
    if (cinfo->progress != NULL) {
      cd_progress_ptr progress = (cd_progress_ptr) cinfo->progress;
      progress->total_extra_passes++; /* count file input as separate pass */
    }
    source->pub.get_pixel_rows = load_interlaced_image;
  } else {
    source->pub.get_pixel_rows = get_pixel_rows;
  }

  /* Create compressor input buffer. */
  source->pub.buffer = (*cinfo->mem->alloc_sarray)
    ((j_common_ptr) cinfo, JPOOL_IMAGE,
     (JDIMENSION) width * NUMCOLORS, (JDIMENSION) 1);
  source->pub.buffer_height = 1;

  /* Return info about the image. */
  cinfo->in_color_space = JCS_RGB;
  cinfo->input_components = NUMCOLORS;
  cinfo->data_precision = BITS_IN_JSAMPLE; /* we always rescale data to this */
  cinfo->image_width = width;
  cinfo->image_height = height;

  TRACEMS3(cinfo, 1, JTRC_GIF, width, height, colormaplen);
}


/*
 * Read one row of pixels.
 * This version is used for noninterlaced GIF images:
 * we read directly from the GIF file.
 */

METHODDEF(JDIMENSION)
get_pixel_rows (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)
{
  gif_source_ptr source = (gif_source_ptr) sinfo;
  register int c;
  register JSAMPROW ptr;
  register JDIMENSION col;
  register JSAMPARRAY colormap = source->colormap;
  
  ptr = source->pub.buffer[0];
  for (col = cinfo->image_width; col > 0; col--) {
    c = LZWReadByte(source);
    *ptr++ = colormap[CM_RED][c];
    *ptr++ = colormap[CM_GREEN][c];
    *ptr++ = colormap[CM_BLUE][c];
  }
  return 1;
}


/*
 * Read one row of pixels.
 * This version is used for the first call on get_pixel_rows when
 * reading an interlaced GIF file: we read the whole image into memory.
 */

METHODDEF(JDIMENSION)
load_interlaced_image (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)
{
  gif_source_ptr source = (gif_source_ptr) sinfo;
  JSAMPARRAY image_ptr;
  register JSAMPROW sptr;
  register JDIMENSION col;
  JDIMENSION row;
  cd_progress_ptr progress = (cd_progress_ptr) cinfo->progress;

  /* Read the interlaced image into the virtual array we've created. */
  for (row = 0; row < cinfo->image_height; row++) {
    if (progress != NULL) {
      progress->pub.pass_counter = (long) row;
      progress->pub.pass_limit = (long) cinfo->image_height;
      (*progress->pub.progress_monitor) ((j_common_ptr) cinfo);
    }
    image_ptr = (*cinfo->mem->access_virt_sarray)
      ((j_common_ptr) cinfo, source->interlaced_image,
       row, (JDIMENSION) 1, TRUE);
    sptr = image_ptr[0];
    for (col = cinfo->image_width; col > 0; col--) {
      *sptr++ = (JSAMPLE) LZWReadByte(source);
    }
  }
  if (progress != NULL)
    progress->completed_extra_passes++;

  /* Replace method pointer so subsequent calls don't come here. */
  source->pub.get_pixel_rows = get_interlaced_row;
  /* Initialize for get_interlaced_row, and perform first call on it. */
  source->cur_row_number = 0;
  source->pass2_offset = (cinfo->image_height + 7) / 8;
  source->pass3_offset = source->pass2_offset + (cinfo->image_height + 3) / 8;
  source->pass4_offset = source->pass3_offset + (cinfo->image_height + 1) / 4;

  return get_interlaced_row(cinfo, sinfo);
}


/*
 * Read one row of pixels.
 * This version is used for interlaced GIF images:
 * we read from the virtual array.
 */

METHODDEF(JDIMENSION)
get_interlaced_row (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)
{
  gif_source_ptr source = (gif_source_ptr) sinfo;
  JSAMPARRAY image_ptr;
  register int c;
  register JSAMPROW sptr, ptr;
  register JDIMENSION col;
  register JSAMPARRAY colormap = source->colormap;
  JDIMENSION irow;

  /* Figure out which row of interlaced image is needed, and access it. */
  switch ((int) (source->cur_row_number & 7)) {
  case 0:			/* first-pass row */
    irow = source->cur_row_number >> 3;
    break;
  case 4:			/* second-pass row */
    irow = (source->cur_row_number >> 3) + source->pass2_offset;
    break;
  case 2:			/* third-pass row */
  case 6:
    irow = (source->cur_row_number >> 2) + source->pass3_offset;
    break;
  default:			/* fourth-pass row */
    irow = (source->cur_row_number >> 1) + source->pass4_offset;
    break;
  }
  image_ptr = (*cinfo->mem->access_virt_sarray)
    ((j_common_ptr) cinfo, source->interlaced_image,
     irow, (JDIMENSION) 1, FALSE);
  /* Scan the row, expand colormap, and output */
  sptr = image_ptr[0];
  ptr = source->pub.buffer[0];
  for (col = cinfo->image_width; col > 0; col--) {
    c = GETJSAMPLE(*sptr++);
    *ptr++ = colormap[CM_RED][c];
    *ptr++ = colormap[CM_GREEN][c];
    *ptr++ = colormap[CM_BLUE][c];
  }
  source->cur_row_number++;	/* for next time */
  return 1;
}


/*
 * Finish up at the end of the file.
 */

METHODDEF(void)
finish_input_gif (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)
{
  /* no work */
}


/*
 * The module selection routine for GIF format input.
 */

GLOBAL(cjpeg_source_ptr)
jinit_read_gif (j_compress_ptr cinfo)
{
  gif_source_ptr source;

  /* Create module interface object */
  source = (gif_source_ptr)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
				  SIZEOF(gif_source_struct));
  source->cinfo = cinfo;	/* make back link for subroutines */
  /* Fill in method ptrs, except get_pixel_rows which start_input sets */
  source->pub.start_input = start_input_gif;
  source->pub.finish_input = finish_input_gif;

  return (cjpeg_source_ptr) source;
}

#endif /* GIF_SUPPORTED */