text: /*
   * Copyright (c) 2014, Julien Bernard
   *
   * Permission to use, copy, modify, and/or distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
   * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
   * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   */
  #include <mm/slope.h>
  
  #include <cmath>
  
  namespace mm {
  
    heightmap slope::operator()(const heightmap& src) {
      heightmap map(size_only, src);
  
      for (heightmap::size_type x = 0; x < src.width(); ++x) {
        for (heightmap::size_type y = 0; y < src.height(); ++y) {
          const double altitude_here = src(x, y);
          double altitude_difference_max = 0.0;
  
          src.visit8neighbours(x, y, [altitude_here, &altitude_difference_max](position pos, double altitude_there) {
            double altitude_difference = std::abs(altitude_here - altitude_there);
            if (altitude_difference > altitude_difference_max) {
              altitude_difference_max = altitude_difference;
            }
          });
  
          map(x, y) = altitude_difference_max;
        }
      }
  
      return map;
    }
  
  }
  