gd_png.c

下载来的一个看图软件的源代码

	      register png_byte a = gdAlphaMax -
	      (row_pointers[j][boffset++] >> 1);
	      im->tpixels[j][i] = gdTrueColorAlpha (r, g, b, a);
	    }
	}
      break;
    default:
      /* Palette image, or something coerced to be one */
      for (j = 0; j < height; ++j)
	{
	  for (i = 0; i < width; ++i)
	    {
	      register png_byte idx = row_pointers[j][i];
	      im->pixels[j][i] = idx;
	      open[idx] = 0;
	    }
	}
    }
#ifdef DEBUG
  if (!im->trueColor)
    {
      for (i = num_palette; i < gdMaxColors; ++i)
	{
	  if (!open[i])
	    {
	      fprintf (stderr, "gd-png warning: image data references out-of-range"
		       " color index (%d)\n", i);
	    }
	}
    }
#endif

  if (palette_allocated)
    gdFree (palette);
  gdFree (image_data);
  gdFree (row_pointers);

  return im;
}


void
gdImagePng (gdImagePtr im, FILE * outFile)
{
  gdIOCtx *out = gdNewFileCtx (outFile);
  gdImagePngCtx (im, out);
  out->free (out);
}

void *
gdImagePngPtr (gdImagePtr im, int *size)
{
  void *rv;
  gdIOCtx *out = gdNewDynamicCtx (2048, NULL);
  gdImagePngCtx (im, out);
  rv = gdDPExtractData (out, size);
  out->free (out);
  return rv;
}

/* This routine is based in part on code from Dale Lutz (Safe Software Inc.)
 *  and in part on demo code from Chapter 15 of "PNG: The Definitive Guide"
 *  (http://www.cdrom.com/pub/png/pngbook.html).
 */
void
gdImagePngCtx (gdImagePtr im, gdIOCtx * outfile)
{
  int i, j, bit_depth, interlace_type;
  int width = im->sx;
  int height = im->sy;
  int colors = im->colorsTotal;
  int *open = im->open;
  int mapping[gdMaxColors];	/* mapping[gd_index] == png_index */
  png_byte trans_values[256];
  png_color_16 trans_rgb_value;
  png_color palette[gdMaxColors];
  png_structp png_ptr;
  png_infop info_ptr;
  volatile int transparent = im->transparent;
  volatile int remap = FALSE;


#ifndef PNG_SETJMP_NOT_SUPPORTED
  png_ptr = png_create_write_struct (PNG_LIBPNG_VER_STRING,
			       &gdPngJmpbufStruct, gdPngErrorHandler, NULL);
#else
  png_ptr = png_create_write_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
#endif
  if (png_ptr == NULL)
    {
      fprintf (stderr, "gd-png error: cannot allocate libpng main struct\n");
      return;
    }

  info_ptr = png_create_info_struct (png_ptr);
  if (info_ptr == NULL)
    {
      fprintf (stderr, "gd-png error: cannot allocate libpng info struct\n");
      png_destroy_write_struct (&png_ptr, (png_infopp) NULL);
      return;
    }

#ifndef PNG_SETJMP_NOT_SUPPORTED
  if (setjmp (gdPngJmpbufStruct.jmpbuf))
    {
      fprintf (stderr, "gd-png error: setjmp returns error condition\n");
      png_destroy_write_struct (&png_ptr, &info_ptr);
      return;
    }
#endif

  png_set_write_fn (png_ptr, (void *) outfile, gdPngWriteData, gdPngFlushData);

  /* This is best for palette images, and libpng defaults to it for
     palette images anyway, so we don't need to do it explicitly.
     What to ideally do for truecolor images depends, alas, on the image.
     gd is intentionally imperfect and doesn't spend a lot of time
     fussing with such things. */
/*  png_set_filter(png_ptr, 0, PNG_FILTER_NONE);  */

  /* may want to force maximum compression, but time penalty is large */
/*  png_set_compression_level(png_ptr, Z_BEST_COMPRESSION);  */

  /* can set this to a smaller value without compromising compression if all
   * image data is 16K or less; will save some decoder memory [min == 8] */
/*  png_set_compression_window_bits(png_ptr, 15);  */

  if (!im->trueColor)
    {
      if (transparent >= im->colorsTotal ||
	  (transparent >= 0 && open[transparent]))
	transparent = -1;
    }
  if (!im->trueColor)
    {
      for (i = 0; i < gdMaxColors; ++i)
	mapping[i] = -1;
    }
  if (!im->trueColor)
    {
      /* count actual number of colors used (colorsTotal == high-water mark) */
      colors = 0;
      for (i = 0; i < im->colorsTotal; ++i)
	{
	  if (!open[i])
	    {
	      mapping[i] = colors;
	      ++colors;
	    }
	}
      if (colors < im->colorsTotal)
	{
	  remap = TRUE;
	}
      if (colors <= 2)
	bit_depth = 1;
      else if (colors <= 4)
	bit_depth = 2;
      else if (colors <= 16)
	bit_depth = 4;
      else
	bit_depth = 8;
    }
  interlace_type = im->interlace ? PNG_INTERLACE_ADAM7 : PNG_INTERLACE_NONE;

  if (im->trueColor)
    {
      if (im->saveAlphaFlag)
	{
	  png_set_IHDR (png_ptr, info_ptr, width, height, 8,
			PNG_COLOR_TYPE_RGB_ALPHA, interlace_type,
		     PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
	}
      else
	{
	  png_set_IHDR (png_ptr, info_ptr, width, height, 8,
			PNG_COLOR_TYPE_RGB, interlace_type,
		     PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
	}
    }
  else
    {
      png_set_IHDR (png_ptr, info_ptr, width, height, bit_depth,
		    PNG_COLOR_TYPE_PALETTE, interlace_type,
		    PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
    }
  if (im->trueColor && (!im->saveAlphaFlag) && (transparent >= 0))
    {
      trans_rgb_value.red = gdTrueColorGetRed (im->trueColor);
      trans_rgb_value.green = gdTrueColorGetGreen (im->trueColor);
      trans_rgb_value.blue = gdTrueColorGetBlue (im->trueColor);
      png_set_tRNS (png_ptr, info_ptr, 0, 0, &trans_rgb_value);
    }
  if (!im->trueColor)
    {
      /* Oy veh. Remap the PNG palette to put the 
         entries with interesting alpha channel
         values first. This minimizes the size
         of the tRNS chunk and thus the size
         of the PNG file as a whole. */
      int tc = 0;
      int i;
      int j;
      int k;
      int highTrans = -1;
      for (i = 0; (i < im->colorsTotal); i++)
	{
	  if ((!im->open[i]) &&
	      (im->alpha[i] != gdAlphaOpaque))
	    {
	      tc++;
	    }
	}
      if (tc)
	{
#if 0
	  for (i = 0; (i < im->colorsTotal); i++)
	    {
	      trans_values[i] = 255 -
		((im->alpha[i] << 1) +
		 (im->alpha[i] >> 7));
	    }
	  png_set_tRNS (png_ptr, info_ptr, trans_values, 256, NULL);
#endif
	  if (!remap)
	    {
	      remap = TRUE;
	    }
	  /* (Semi-)transparent indexes come up from the bottom
	     of the list of real colors; opaque
	     indexes come down from the top */
	  j = 0;
	  k = colors - 1;
	  for (i = 0; (i < im->colorsTotal); i++)
	    {
	      if (!im->open[i])
		{
		  if (im->alpha[i] != gdAlphaOpaque)
		    {
		      trans_values[j] = 255 -
			((im->alpha[i] << 1) +
			 (im->alpha[i] >> 7));
		      mapping[i] = j++;
		    }
		  else
		    {
		      mapping[i] = k--;
		    }
		}
	    }
	  png_set_tRNS (png_ptr, info_ptr, trans_values, tc, NULL);
	}
    }

  /* convert palette to libpng layout */
  if (!im->trueColor)
    {
      if (remap)
	for (i = 0; i < im->colorsTotal; ++i)
	  {
	    if (mapping[i] < 0)
	      continue;
	    palette[mapping[i]].red = im->red[i];
	    palette[mapping[i]].green = im->green[i];
	    palette[mapping[i]].blue = im->blue[i];
	  }
      else
	for (i = 0; i < colors; ++i)
	  {
	    palette[i].red = im->red[i];
	    palette[i].green = im->green[i];
	    palette[i].blue = im->blue[i];
	  }
      png_set_PLTE (png_ptr, info_ptr, palette, colors);
    }

  /* write out the PNG header info (everything up to first IDAT) */
  png_write_info (png_ptr, info_ptr);

  /* make sure < 8-bit images are packed into pixels as tightly as possible */
  png_set_packing (png_ptr);

  /* This code allocates a set of row buffers and copies the gd image data
   * into them only in the case that remapping is necessary; in gd 1.3 and
   * later, the im->pixels array is laid out identically to libpng's row
   * pointers and can be passed to png_write_image() function directly.
   * The remapping case could be accomplished with less memory for non-
   * interlaced images, but interlacing causes some serious complications. */
  if (im->trueColor)
    {
      int channels = im->saveAlphaFlag ? 4 : 3;
      /* Our little 7-bit alpha channel trick costs us a bit here. */
      png_bytep *row_pointers;
      row_pointers = gdMalloc (sizeof (png_bytep) * height);
      if (row_pointers == NULL)
	{
	  fprintf (stderr, "gd-png error: unable to allocate row_pointers\n");
	}
      for (j = 0; j < height; ++j)
	{
	  int bo = 0;
	  if ((row_pointers[j] = (png_bytep) gdMalloc (width * channels)) == NULL)
	    {
	      fprintf (stderr, "gd-png error: unable to allocate rows\n");
	      for (i = 0; i < j; ++i)
		gdFree (row_pointers[i]);
	      return;
	    }
	  for (i = 0; i < width; ++i)
	    {
	      unsigned char a;
	      row_pointers[j][bo++] = gdTrueColorGetRed (im->tpixels[j][i]);
	      row_pointers[j][bo++] = gdTrueColorGetGreen (im->tpixels[j][i]);
	      row_pointers[j][bo++] = gdTrueColorGetBlue (im->tpixels[j][i]);
	      if (im->saveAlphaFlag)
		{
		  /* convert the 7-bit alpha channel to an 8-bit alpha channel.
		     We do a little bit-flipping magic, repeating the MSB
		     as the LSB, to ensure that 0 maps to 0 and
		     127 maps to 255. We also have to invert to match
		     PNG's convention in which 255 is opaque. */
		  a = gdTrueColorGetAlpha (im->tpixels[j][i]);
		  row_pointers[j][bo++] = 255 - ((a << 1) + (a >> 7));
		}
	    }
	}

      png_write_image (png_ptr, row_pointers);
      png_write_end (png_ptr, info_ptr);

      for (j = 0; j < height; ++j)
	gdFree (row_pointers[j]);
      gdFree (row_pointers);
    }
  else
    {
      if (remap)
	{
	  png_bytep *row_pointers;
	  row_pointers = gdMalloc (sizeof (png_bytep) * height);
	  if (row_pointers == NULL)
	    {
	      fprintf (stderr, "gd-png error: unable to allocate row_pointers\n");
	    }
	  for (j = 0; j < height; ++j)
	    {
	      if ((row_pointers[j] = (png_bytep) gdMalloc (width)) == NULL)
		{
		  fprintf (stderr, "gd-png error: unable to allocate rows\n");
		  for (i = 0; i < j; ++i)
		    gdFree (row_pointers[i]);
		  return;
		}
	      for (i = 0; i < width; ++i)
		row_pointers[j][i] = mapping[im->pixels[j][i]];
	    }

	  png_write_image (png_ptr, row_pointers);
	  png_write_end (png_ptr, info_ptr);

	  for (j = 0; j < height; ++j)
	    gdFree (row_pointers[j]);
	  gdFree (row_pointers);
	}
      else
	{
	  png_write_image (png_ptr, im->pixels);
	  png_write_end (png_ptr, info_ptr);
	}
    }
  /* 1.6.3: maybe we should give that memory BACK! TBB */
  png_destroy_write_struct (&png_ptr, &info_ptr);
}


#endif /* HAVE_LIBPNG */