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src/Source/LibJPEG/wrgif.c  view on Meta::CPAN

  /* Flush the packet buffer */
  flush_packet(dinfo);
}


/* GIF header construction */


LOCAL(void)
put_word (gif_dest_ptr dinfo, unsigned int w)
/* Emit a 16-bit word, LSB first */
{
  putc(w & 0xFF, dinfo->pub.output_file);
  putc((w >> 8) & 0xFF, dinfo->pub.output_file);
}


LOCAL(void)
put_3bytes (gif_dest_ptr dinfo, int val)
/* Emit 3 copies of same byte value --- handy subr for colormap construction */
{
  putc(val, dinfo->pub.output_file);
  putc(val, dinfo->pub.output_file);
  putc(val, dinfo->pub.output_file);
}


LOCAL(void)
emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap)
/* Output the GIF file header, including color map */
/* If colormap==NULL, synthesize a gray-scale colormap */
{
  int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte;
  int cshift = dinfo->cinfo->data_precision - 8;
  int i;

  if (num_colors > 256)
    ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors);
  /* Compute bits/pixel and related values */
  BitsPerPixel = 1;
  while (num_colors > (1 << BitsPerPixel))
    BitsPerPixel++;
  ColorMapSize = 1 << BitsPerPixel;
  if (BitsPerPixel <= 1)
    InitCodeSize = 2;
  else
    InitCodeSize = BitsPerPixel;
  /*
   * Write the GIF header.
   * Note that we generate a plain GIF87 header for maximum compatibility.
   */
  putc('G', dinfo->pub.output_file);
  putc('I', dinfo->pub.output_file);
  putc('F', dinfo->pub.output_file);
  putc('8', dinfo->pub.output_file);
  putc('7', dinfo->pub.output_file);
  putc('a', dinfo->pub.output_file);
  /* Write the Logical Screen Descriptor */
  put_word(dinfo, (unsigned int) dinfo->cinfo->output_width);
  put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
  FlagByte = 0x80;		/* Yes, there is a global color table */
  FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */
  FlagByte |= (BitsPerPixel-1);	/* size of global color table */
  putc(FlagByte, dinfo->pub.output_file);
  putc(0, dinfo->pub.output_file); /* Background color index */
  putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */
  /* Write the Global Color Map */
  /* If the color map is more than 8 bits precision, */
  /* we reduce it to 8 bits by shifting */
  for (i=0; i < ColorMapSize; i++) {
    if (i < num_colors) {
      if (colormap != NULL) {
	if (dinfo->cinfo->out_color_space == JCS_RGB) {
	  /* Normal case: RGB color map */
	  putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file);
	  putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file);
	  putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file);
	} else {
	  /* Grayscale "color map": possible if quantizing grayscale image */
	  put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift);
	}
      } else {
	/* Create a gray-scale map of num_colors values, range 0..255 */
	put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1));
      }
    } else {
      /* fill out the map to a power of 2 */
      put_3bytes(dinfo, 0);
    }
  }
  /* Write image separator and Image Descriptor */
  putc(',', dinfo->pub.output_file); /* separator */
  put_word(dinfo, 0);		/* left/top offset */
  put_word(dinfo, 0);
  put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */
  put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
  /* flag byte: not interlaced, no local color map */
  putc(0x00, dinfo->pub.output_file);
  /* Write Initial Code Size byte */
  putc(InitCodeSize, dinfo->pub.output_file);

  /* Initialize for "compression" of image data */
  compress_init(dinfo, InitCodeSize+1);
}


/*
 * Startup: write the file header.
 */

METHODDEF(void)
start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
{
  gif_dest_ptr dest = (gif_dest_ptr) dinfo;

  if (cinfo->quantize_colors)
    emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap);
  else
    emit_header(dest, 256, (JSAMPARRAY) NULL);
}


/*