readerwriterjpeg.cpp

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 * (ignoring the current state of next_output_byte & free_in_buffer),
 * reset the pointer & count to the start of the buffer, and return TRUE
 * indicating that the buffer has been dumped.
 *
 * In applications that need to be able to suspend compression due to output
 * overrun, a FALSE return indicates that the buffer cannot be emptied now.
 * In this situation, the compressor will return to its caller (possibly with
 * an indication that it has not accepted all the supplied scanlines).  The
 * application should resume compression after it has made more room in the
 * output buffer.  Note that there are substantial restrictions on the use of
 * suspension --- see the documentation.
 *
 * When suspending, the compressor will back up to a convenient restart point
 * (typically the start of the current MCU). next_output_byte & free_in_buffer
 * indicate where the restart point will be if the current call returns FALSE.
 * Data beyond this point will be regenerated after resumption, so do not
 * write it out when emptying the buffer externally.
 */

boolean empty_output_buffer (j_compress_ptr cinfo)
{
  stream_dest_ptr dest = (stream_dest_ptr) cinfo->dest;

  dest->outfile->write((const char*)dest->buffer,OUTPUT_BUF_SIZE);
  if (dest->outfile->bad())
    ERREXIT(cinfo, JERR_FILE_WRITE);

  dest->pub.next_output_byte = dest->buffer;
  dest->pub.free_in_buffer = OUTPUT_BUF_SIZE;

  return TRUE;
}


/*
 * Terminate destination --- called by jpeg_finish_compress
 * after all data has been written.  Usually needs to flush buffer.
 *
 * NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
 * application must deal with any cleanup that should happen even
 * for error exit.
 */

void term_destination (j_compress_ptr cinfo)
{
  stream_dest_ptr dest = (stream_dest_ptr) cinfo->dest;
  size_t datacount = OUTPUT_BUF_SIZE - dest->pub.free_in_buffer;

  /* Write any data remaining in the buffer */
  if (datacount > 0) {
    dest->outfile->write((const char*)dest->buffer,datacount);
    if (dest->outfile->bad())
      ERREXIT(cinfo, JERR_FILE_WRITE);
  }
  dest->outfile->flush();
  /* Make sure we wrote the output file OK */
  if (dest->outfile->bad())
    ERREXIT(cinfo, JERR_FILE_WRITE);
}


/*
 * Prepare for output to a stdio stream.
 * The caller must have already opened the stream, and is responsible
 * for closing it after finishing compression.
 */

void jpeg_stream_dest (j_compress_ptr cinfo, std::ostream * outfile)
{
    stream_dest_ptr dest;

    /* The destination object is made permanent so that multiple JPEG images
     * can be written to the same file without re-executing jpeg_stdio_dest.
     * This makes it dangerous to use this manager and a different destination
     * manager serially with the same JPEG object, because their private object
     * sizes may be different.  Caveat programmer.
     */
    if (cinfo->dest == NULL) {    /* first time for this JPEG object? */
        cinfo->dest = (struct jpeg_destination_mgr *)
            (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT, sizeof(stream_destination_mgr));
    }

    dest = (stream_dest_ptr) cinfo->dest;
    dest->pub.init_destination = init_destination;
    dest->pub.empty_output_buffer = empty_output_buffer;
    dest->pub.term_destination = term_destination;
    dest->outfile = outfile;
}

/* END OF READ/WRITE STREAM CODE */

int
simage_jpeg_error(char * buffer, int buflen)
{
    switch (jpegerror)
    {
        case ERR_OPEN:
            strncpy(buffer, "JPEG loader: Error opening file", buflen);
            break;
        case ERR_MEM:
            strncpy(buffer, "JPEG loader: Out of memory error", buflen);
            break;
        case ERR_JPEGLIB:
            strncpy(buffer, "JPEG loader: Illegal jpeg file", buflen);
            break;
    }
    return jpegerror;
}


struct my_error_mgr
{
    struct jpeg_error_mgr pub;   /* "public" fields */

    jmp_buf setjmp_buffer;       /* for return to caller */
};

typedef struct my_error_mgr * my_error_ptr;

static void
my_error_exit (j_common_ptr cinfo)
{
    /* cinfo->err really points to a my_error_mgr struct, so coerce pointer */
    my_error_ptr myerr = (my_error_ptr) cinfo->err;

    /* Always display the message. */
    /* We could postpone this until after returning, if we chose. */
    /*(*cinfo->err->output_message) (cinfo);*/

    /* FIXME: get error messahe from jpeglib */

    /* Return control to the setjmp point */
    longjmp(myerr->setjmp_buffer, 1);
}


int
simage_jpeg_identify(const char *,
const unsigned char *header,
int headerlen)
{
    static unsigned char jpgcmp[] = {'J', 'F', 'I', 'F' };
    if (headerlen < 4) return 0;
    if (memcmp((const void*)&header[6],
        (const void*)jpgcmp, 4) == 0) return 1;
    return 0;
}


static unsigned char*
copyScanline(unsigned char *currPtr, unsigned char *from, int cnt)
{
    memcpy((void*)currPtr, (void*)from, cnt);
    currPtr -= cnt;
    return currPtr;
}

unsigned char *
simage_jpeg_load(std::istream& fin,
int *width_ret,
int *height_ret,
int *numComponents_ret)
{
    int width;
    int height;
    unsigned char *currPtr;
    int format;
    /* This struct contains the JPEG decompression parameters and pointers to
     * working space (which is allocated as needed by the JPEG library).
     */
    struct jpeg_decompress_struct cinfo;
    /* We use our private extension JPEG error handler.
     * Note that this struct must live as long as the main JPEG parameter
     * struct, to avoid dangling-pointer problems.
     */
    struct my_error_mgr jerr;
    /* More stuff */
    //FILE * infile;               /* source file */
    JSAMPARRAY rowbuffer;        /* Output row buffer */
    int row_stride;              /* physical row width in output buffer */

    jpegerror = ERR_NO_ERROR;

    /* In this example we want to open the input file before doing anything else,
     * so that the setjmp() error recovery below can assume the file is open.
     * VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
     * requires it in order to read binary files.
     */

    /*if ((infile = fopen(filename, "rb")) == NULL)
    {
        jpegerror = ERR_OPEN;
        return NULL;
    }*/

    /* Step 1: allocate and initialize JPEG decompression object */

    /* We set up the normal JPEG error routines, then override error_exit. */
    cinfo.err = jpeg_std_error(&jerr.pub);
    jerr.pub.error_exit = my_error_exit;
    /* Establish the setjmp return context for my_error_exit to use. */
    if (setjmp(jerr.setjmp_buffer))
    {
        /* If we get here, the JPEG code has signaled an error.
         * We need to clean up the JPEG object, close the input file, and return.
         */
        jpegerror = ERR_JPEGLIB;
        jpeg_destroy_decompress(&cinfo);
        //fclose(infile);
        //if (buffer) delete [] buffer;
        return NULL;
    }

    // used to be before setjump above, but have moved to after to avoid compile warnings.
    unsigned char *buffer = NULL;

    /* Now we can initialize the JPEG decompression object. */
    jpeg_create_decompress(&cinfo);

    /* Step 2: specify data source (eg, a file) */

    //jpeg_stdio_src(&cinfo, infile);
    jpeg_istream_src(&cinfo,&fin);

    /* Step 3: read file parameters with jpeg_read_header() */

    (void) jpeg_read_header(&cinfo, TRUE);
    /* We can ignore the return value from jpeg_read_header since
     *   (a) suspension is not possible with the stdio data source, and
     *   (b) we passed TRUE to reject a tables-only JPEG file as an error.
     * See libjpeg.doc for more info.
     */

    /* Step 4: set parameters for decompression */
    /* In this example, we don't need to change any of the defaults set by
     * jpeg_read_header(), so we do nothing here.
     */

    /* Step 5: Start decompressor */
    if (cinfo.jpeg_color_space == JCS_GRAYSCALE)
    {
        format = 1;
        cinfo.out_color_space = JCS_GRAYSCALE;
    }
    else                         /* use rgb */
    {
        format = 3;
        cinfo.out_color_space = JCS_RGB;
    }

    (void) jpeg_start_decompress(&cinfo);
    /* We can ignore the return value since suspension is not possible
     * with the stdio data source.
     */

    /* We may need to do some setup of our own at this point before reading
     * the data.  After jpeg_start_decompress() we have the correct scaled
     * output image dimensions available, as well as the output colormap
     * if we asked for color quantization.
     * In this example, we need to make an output work buffer of the right size.
     */
    /* JSAMPLEs per row in output buffer */
    row_stride = cinfo.output_width * cinfo.output_components;
    /* Make a one-row-high sample array that will go away when done with image */
    rowbuffer = (*cinfo.mem->alloc_sarray)
        ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);
    width = cinfo.output_width;
    height = cinfo.output_height;
    buffer = currPtr = new unsigned char [width*height*cinfo.output_components];

    /* Step 6: while (scan lines remain to be read) */
    /*           jpeg_read_scanlines(...); */

    /* Here we use the library's state variable cinfo.output_scanline as the
     * loop counter, so that we don't have to keep track ourselves.
     */

    /* flip image upside down */
    if (buffer)
    {
        currPtr = buffer + row_stride * (cinfo.output_height-1);

        while (cinfo.output_scanline < cinfo.output_height)
        {