to_ppm.c

#include <stdio.h>
#include <setjmp.h>

#define HAVE_PROTOTYPES
#include <jpeglib.h>
#pragma CHECKED_SCOPE on

void put_scanline_someplace(JSAMPROW buffer : count(row_stride), int row_stride) {
  for (int i = 0; i < row_stride; i++)
    printf("%3d ", buffer[i]);
  printf("\n");
}

struct my_error_mgr {
  struct jpeg_error_mgr pub;	/* "public" fields */
  jmp_buf setjmp_buffer : itype(struct __jmp_buf_tag _Checked[1]);	/* for return to caller */
};

typedef _Ptr<struct my_error_mgr> my_error_ptr;

/*
 * Here's the routine that will replace the standard error_exit method:
 */

METHODDEF(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 = _Dynamic_bounds_cast<_Ptr<struct my_error_mgr>>(cinfo->err);

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

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


/*
 * Sample routine for JPEG decompression.  We assume that the source file name
 * is passed in.  We want to return 1 on success, 0 on error.
 */


GLOBAL(int)
read_JPEG_file (_Nt_array_ptr<char> filename)
{

  /* 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 */
  _Ptr<FILE> infile = ((void *)0);		/* source file */
  JSAMPARRAY buffer : count(1) = ((void *)0);		/* Output row buffer */
  int row_stride;		/* physical row width in output buffer */

  /* 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) {
    fprintf(stderr, "can't open %s\n", filename);
    return 0;
  }

  /* 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. */
  int jmp = 0;
  _Unchecked { jmp = setjmp(jerr.setjmp_buffer); }
  if (jmp) {
    /* 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.
     */
    jpeg_destroy_decompress(&cinfo);
    fclose(infile);
    return 0;
  }
  /* 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);

  /* 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.txt 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 */

  (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 */
  buffer = (*cinfo.mem->alloc_sarray)
		((_Ptr<struct jpeg_common_struct>) &cinfo, JPOOL_IMAGE, row_stride, 1);

  if (cinfo.output_components == 1) {
    printf("P2\n");
  } else if (cinfo.output_components == 3) {
    printf("P3\n");
  } else {
    _Unchecked { longjmp(jerr.setjmp_buffer, 1); }
  }
  printf("%d %d\n255\n", cinfo.output_width, cinfo.output_height);

  /* 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.
   */
  while (cinfo.output_scanline < cinfo.output_height) {
    /* jpeg_read_scanlines expects an array of pointers to scanlines.
     * Here the array is only one element long, but you could ask for
     * more than one scanline at a time if that's more convenient.
     */
    (void) jpeg_read_scanlines(&cinfo, buffer, 1);
    /* Assume put_scanline_someplace wants a pointer and sample count. */
    JSAMPROW row_unkb : bounds(unknown) = buffer[0];
    JSAMPROW row : count(row_stride) = 0;
    _Unchecked {
      row = _Assume_bounds_cast<JSAMPROW>(row_unkb,  count(row_stride));
    }
    put_scanline_someplace(row, row_stride);
  }

  /* Step 7: Finish decompression */

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

  /* Step 8: Release JPEG decompression object */

  /* This is an important step since it will release a good deal of memory. */
  jpeg_destroy_decompress(&cinfo);

  /* After finish_decompress, we can close the input file.
   * Here we postpone it until after no more JPEG errors are possible,
   * so as to simplify the setjmp error logic above.  (Actually, I don't
   * think that jpeg_destroy can do an error exit, but why assume anything...)
   */
  fclose(infile);

  /* At this point you may want to check to see whether any corrupt-data
   * warnings occurred (test whether jerr.pub.num_warnings is nonzero).
   */

  /* And we're done! */
  return 1;
}


int main(int argc, _Array_ptr<_Nt_array_ptr<char>> argv : count(argc)) {
  _Nt_array_ptr<char> file = argv[1];
  return read_JPEG_file(file);
}