/*
 *  Read png files.
 */

#include "config.h"

#if HAVE_LIBPNG

#include "pngread.h"
#include "png.h"
#include <stdio.h>
#include <stdlib.h>

static double get_gamma_exp( void );
static int pngreadstr( FILE *fp,
		       int *w, int *h, int *nc,
		       png_structp png_ptr,
		       png_infop info_ptr,
		       unsigned char **pixels,
		       unsigned char ***rows );


unsigned char *pngread (FILE *fp, int *w, int *h, int *nc)
{
  png_structp png_ptr;
  png_infop info_ptr;
  unsigned char *pixels = 0, **rows = 0;

  /* Create and initialize the png_struct with the desired error handler
    * functions.  If you want to use the default stderr and longjump method,
    * you can supply NULL for the last three parameters.  We also supply the
    * the compiler header file version, so that we know if the application
    * was compiled with a compatible version of the library.  REQUIRED
    */
  png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0);
 
  if (png_ptr == NULL) return 0;
 
   /* Allocate/initialize the memory for image information.  REQUIRED. */
  info_ptr = png_create_info_struct(png_ptr);
  if (info_ptr == NULL)
    {
      png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
      return 0;
    }

  /* png_ptr and info_ptr are freed in pngreadstr */
  if (! pngreadstr( fp, w, h, nc, png_ptr, info_ptr, &pixels, &rows ))
    {
      /* Free all of the memory associated with the png_ptr and info_ptr */
      png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);

      if (pixels) free(pixels);
      if (rows) free(rows);
      return 0;
    }

  if (rows) free(rows);
  return pixels;
}

/* This is broken out into a separate function so the setjmp
 * can't clobber pixels and rows.
 */

static int pngreadstr( FILE *fp,
		       int *w, int *h, int *nc,
		       png_structp png_ptr,
		       png_infop info_ptr,
		       unsigned char **ppixels,
		       unsigned char ***prows )
{
  png_uint_32 width, height;
  int bit_depth, color_type, interlace_type;
  int bytes_per_row, row;
  int gray_palette;
  unsigned char *pixels, **rows;


  /* Set error handling if you are using the setjmp/longjmp method (this is
    * the normal method of doing things with libpng).  REQUIRED unless you
    * set up your own error handlers in the png_create_read_struct() earlier.
    */
  if (setjmp(png_ptr->jmpbuf))
    {
      /* If we get here, we had a problem reading the file */
      return 0;
    }
 
  /* Set up the input control if you are using standard C streams */
  png_init_io(png_ptr, fp);

  /* The call to png_read_info() gives us all of the information from the
   * PNG file before the first IDAT (image data chunk).  REQUIRED
   */
  png_read_info(png_ptr, info_ptr);
 
  png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
	       &interlace_type, NULL, NULL);
 
  *nc = png_get_channels(png_ptr, info_ptr);
  /*printf("color_type %d, nc = %d ", color_type, *nc);*/

/**** Set up the data transformations you want.  Note that these are all
 **** optional.  Only call them if you want/need them.  Many of the
 **** transformations only work on specific types of images, and many
 **** are mutually exclusive.
 ****/
 
  /* tell libpng to strip 16 bit/color files down to 8 bits/color */
  png_set_strip_16(png_ptr);

  /* Extract multiple pixels with bit depths of 1, 2, and 4 from a single
   * byte into separate bytes (useful for paletted and grayscale images).
   */
  png_set_packing(png_ptr);

  /* Expand paletted colors into true RGB triplets */
  if (color_type == PNG_COLOR_TYPE_PALETTE)
    {
      /* Even gray paletted images will get expanded here */
      png_set_expand(png_ptr);
      *nc = 3;
    }
 
  /* Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel */
  if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
    png_set_expand(png_ptr);
 
  /* Expand paletted or RGB images with transparency to full alpha channels
   * so the data will be available as RGBA quartets.
   */
  if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
    {
      png_set_expand(png_ptr);
      ++(*nc);
    }

  gray_palette = 0;
  if (color_type == PNG_COLOR_TYPE_PALETTE)
    {
      int n, num_palette;
      png_colorp palette;
      if (png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette))
	{
	  gray_palette = 1;
	  for (n=0; n<num_palette; ++n)
	    if (palette[n].red != palette[n].green ||
		palette[n].blue != palette[n].green)
	      {
		gray_palette = 0;
		break;
	      }
	}
    }

  /* set gamma */
  {
    double file_gamma, default_exponent = get_gamma_exp();
    if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
      png_set_gamma(png_ptr, default_exponent, file_gamma);
    else
      png_set_gamma(png_ptr, default_exponent, 0.45455);
  }

  /* Get updated info */
  png_read_update_info(png_ptr, info_ptr);
  png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
	       &interlace_type, NULL, NULL);
 
  /* Allocate the memory to hold the image using the fields of info_ptr. */
  bytes_per_row = *nc * width;

  *ppixels = (unsigned char*) malloc(bytes_per_row * height);
  *prows = (unsigned char**) malloc(height * sizeof(char *));
  if (*ppixels == 0 || *prows == 0)
    {
      /* Free all of the memory associated with the png_ptr and info_ptr */
      png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);
      return 0;
    }

  pixels = *ppixels;
  rows = *prows;
  for (row=0; row<height; ++row)
    rows[row] = &pixels[row * bytes_per_row];

  /* Now it's time to read the image.  One of these methods is REQUIRED */
  /* Read the entire image in one go */
  png_read_image(png_ptr, rows);
 
  /* read rest of file, and get additional chunks in info_ptr - REQUIRED */
  png_read_end(png_ptr, info_ptr);
 
  /* clean up after the read, and free any memory allocated - REQUIRED */
  png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);

  /* Reduce gray palette images down to intensity or intensity/alpha */
  if (gray_palette)
    {
      int n, np = width * height;
      if (*nc == 3)
	{
	  for (n=1; n<np; ++n)
	    pixels[n] = pixels[3*n];
	  *nc = 1;
	}
      else if (*nc == 4)
	{
	  for (n=0; n<np; ++n) {
	    pixels[2*n] = pixels[4*n];
	    pixels[2*n+1] = pixels[4*n+3];
	  }
	  *nc = 2;
	}
    }

  *w = width;
  *h = height;
  return 1;
}

/* From Greg Roelofs */

static double get_gamma_exp()
{
  static double default_exponent = 2.2;
  static int set = 0;

  if (! set)
    {

#if defined(NeXT)
      default_exponent = 1.0;   /* 2.2/next_gamma for 3rd-party utils */

#elif defined(sgi)
      default_exponent = 1.3;   /* default == 2.2 / 1.7 */
      /* there doesn't seem to be any documented function to get the
   * "gamma" value, so we do it the hard way */
      FILE *infile;
      if (infile = fopen("/etc/config/system.glGammaVal", "r")) {
	double sgi_gamma;
	char fooline[80];
	fgets(fooline, sizeof(fooline), infile);
	fclose(infile);
	sgi_gamma = atof(fooline);
	if (sgi_gamma > 0.0)
	  default_exponent = 2.2 / sgi_gamma;
      }

#elif defined(Macintosh)
      default_exponent = 1.5;   /* default == (1.8/2.61) * 2.2 */
      /*
	if (mac_gamma = some_mac_function_that_returns_gamma())
	default_exponent = (mac_gamma/2.61) * 2.2;
	*/

#endif

      set = 1;
    }

  return default_exponent;
}

#endif /* HAVE_LIBPNG */