/* jpegread.c  needs jpeglib.h and libjpeg.a */
/* jpegread given a filename.jpg, alpha, returns width, height, rgb pixels  */
/*     int width, height; int alpha=0 to 255, or -1 for just rgb            */
/*     unsigned char pixels[4*width*height]; or 3*width*height for alpha=-1 */
/* call: status = jpegread("your-filename", alpha, &width, &height, pixels);*/
/* status==0 for OK                                                         */

#include <stdio.h>
#include "jpeglib.h"
#include <setjmp.h>
static void put_scanline(unsigned char buffer[], int line, int width,
                         int height, int alpha, unsigned char rgbpix[]);
static int debug = 0;                /* = 1; prints every pixel */

/* IMAGE DATA FORMATS:
 * The standard input image format is a rectangular array of pixels, with
 * each pixel having the same number of "component" values (color channels).
 * Each pixel row is an array of JSAMPLEs (which typically are unsigned chars).
 * If you are working with color data, then the color values for each pixel
 * must be adjacent in the row; for example, R,G,B,R,G,B,R,G,B,... for 24-bit
 * RGB color. R,G,B,A,R,G,B,A,... for RGB Alpha 32 bits per pixel
 */

/*
 * Scanlines MUST be supplied in top-to-bottom order if you want your JPEG
 * files to be compatible with everyone else's.  If you cannot readily read
 * your data in that order, you'll need an intermediate array to hold the
 * image.  See rdtarga.c or rdbmp.c for examples of handling bottom-to-top
 * source data using the JPEG code's internal virtual-array mechanisms.
 */

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;

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 = (my_error_ptr) 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 */
  longjmp(myerr->setjmp_buffer, 1);
} /* end my_error_exit */

int jpegread(char filename[], int alpha, int * width, int * height,
             unsigned char rgbpix[])
{
  /* 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;
  FILE * infile;		/* source file */
  JSAMPARRAY buffer;		/* Output row buffer */
  int row_stride;		/* physical row width in output buffer */

  if ((infile = fopen(filename, "rb")) == NULL) {
    if(debug)printf("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. */
  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.
     */
    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.doc for more info.
   */

  /* Step 4: set parameters for decompression */

  /* Step 5: Start decompressor */

  (void) jpeg_start_decompress(&cinfo);

  /* 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;

  *width =  cinfo.output_width;;
  *height = cinfo.output_height;

  /* Make a one-row-high sample array that will go away when done with image */
  buffer = (*cinfo.mem->alloc_sarray)
		((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);

  /* 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. */
    if(debug)printf("cinfo.output_scanline=%d\n", cinfo.output_scanline);
    if(debug)printf("cinfo.output_height=%d\n", cinfo.output_height);
    if(debug)printf("row_stride=%d\n", row_stride);
    put_scanline(buffer[0], cinfo.output_scanline, cinfo.output_width,
                 cinfo.output_height, alpha, rgbpix);
  }

  /* 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);
  return 0;
}
/* Scanlines are returned in the same order as they appear in the JPEG file,
 * which is standardly top-to-bottom.  If you must emit data bottom-to-top,
 * you can use one of the virtual arrays provided by the JPEG memory manager
 * to invert the data.  See wrbmp.c for an example.
 */

static void put_scanline(unsigned char buffer[], int line, int width,
                         int height, int alpha, unsigned char rgbpix[])
{
  int i, j, k;

  if(alpha<0 || alpha>255)
  {
    k = (height-line)*3*width;
    for(i=0; i<3*width; i+=3)
    {
      rgbpix[k+i]   = buffer[i];
      rgbpix[k+i+1] = buffer[i+1];
      rgbpix[k+i+2] = buffer[i+2];
    }
  }
  else
  {
    k = (height-line)*4*width;
    j = 0;
    for(i=0; i<3*width; i+=3)
    {
      if(debug)printf("i=%d, j=%d, k=%d, rgb=%03u %03u %03u \n",
             i, j, k, buffer[i], buffer[i+1], buffer[i+2]);
      rgbpix[k+j+i]   = buffer[i];
      rgbpix[k+j+i+1] = buffer[i+1];
      rgbpix[k+j+i+2] = buffer[i+2];
      rgbpix[k+j+i+3] = alpha;
      j++;
    }
  }
} /* end put_scanline */