jdatasrc.c

JPEG转换到BMP的代码

/*note:this is not a core library module, so it doesn't define JPEG_INTERNALS */
 
#include "jinclude.h"
#include "jpeglib.h"
#include "jerror.h"


typedef struct {
  struct jpeg_source_mgr pub;	/* public fields */
	unsigned char *pSourceData;	/*add lurui datasource*/
	int dataLength;
  JOCTET * buffer;		/* start of buffer */
  boolean start_of_file;	/* have we gotten any data yet? */
} my_source_mgr;

typedef my_source_mgr * my_src_ptr;

#define INPUT_BUF_SIZE  4096	/* choose an efficiently fread'able size */


METHODDEF(void)
init_source (j_decompress_ptr cinfo)
{
  my_src_ptr src = (my_src_ptr) cinfo->src;
	if (src->dataLength<=0) 
		ERREXIT(cinfo, JERR_INPUT_EMPTY);
  src->start_of_file = TRUE;
}


METHODDEF(boolean)
fill_input_buffer (j_decompress_ptr cinfo)
{
  my_src_ptr src = (my_src_ptr) cinfo->src;
 size_t nbytes;

  if (!src->start_of_file)
  {
    WARNMS(cinfo, JWRN_JPEG_EOF);
    src->buffer[0] = (JOCTET) 0xFF;
    src->buffer[1] = (JOCTET) JPEG_EOI;
    nbytes = 2;
	src->pub.next_input_byte = src->buffer;
	src->pub.bytes_in_buffer = nbytes;
  }
else
	{
		src->pub.next_input_byte = src->pSourceData;
		src->pub.bytes_in_buffer = src->dataLength;
		src->start_of_file = FALSE;
	}
  return TRUE;
}


METHODDEF(void)
skip_input_data (j_decompress_ptr cinfo, long num_bytes)
{
  my_src_ptr src = (my_src_ptr) cinfo->src;

  if (num_bytes > 0) {
    while (num_bytes > (long) src->pub.bytes_in_buffer) {
      num_bytes -= (long) src->pub.bytes_in_buffer;
      (void) fill_input_buffer(cinfo);
     }
    src->pub.next_input_byte += (size_t) num_bytes;
    src->pub.bytes_in_buffer -= (size_t) num_bytes;
  }
}


METHODDEF(void)
term_source (j_decompress_ptr cinfo)
{
  /* no work necessary here */
}



GLOBAL(void)
jpeg_stdio_src (j_decompress_ptr cinfo, unsigned char *pSourceData, int dataLength)
{
  my_src_ptr src;

  if (cinfo->src == NULL) {	/* first time for this JPEG object? */
    cinfo->src = (struct jpeg_source_mgr *)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
				  SIZEOF(my_source_mgr));
    src = (my_src_ptr) cinfo->src;
    src->buffer = (JOCTET *)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
				  INPUT_BUF_SIZE * SIZEOF(JOCTET));
  }

  src = (my_src_ptr) cinfo->src;
  src->pub.init_source = init_source;
  src->pub.fill_input_buffer = fill_input_buffer;
  src->pub.skip_input_data = skip_input_data;
  src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method */
  src->pub.term_source = term_source;
  src->dataLength=dataLength; 
  src->pSourceData=pSourceData;
  src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
  src->pub.next_input_byte = NULL; /* until buffer loaded */
}