n/f/hetero: add default offset estimation

noise/fractal/hetero.hpp

@@ -37,6 +37,14 @@ namespace util { namespace noise { namespace fractal {
         static constexpr T DEFAULT_GAIN = 1 / DEFAULT_LACUNARITY;
         static constexpr T DEFAULT_OFFSET = T(0.7);
 
+        hetero (seed_t,
+                unsigned octaves,
+                T H,
+                T frequency,
+                T lacunarity,
+                T amplitude,
+                T gain);
+
         hetero (seed_t,
                 unsigned octaves,
                 T H,

noise/fractal/hetero.ipp

@@ -22,6 +22,26 @@
 namespace util { namespace noise { namespace fractal {
     ///////////////////////////////////////////////////////////////////////////
     template <typename T, typename B>
+    hetero<T,B>::hetero(seed_t _seed,
+                        unsigned _octaves,
+                        T _H,
+                        T _frequency,
+                        T _lacunarity,
+                        T _amplitude,
+                        T _gain):
+        hetero<T,B> (_seed,
+                     _octaves,
+                     _H,
+                     _frequency,
+                     _lacunarity,
+                     _amplitude,
+                     _gain,
+                     -this->basis ().bounds ().min + this->basis ().bounds ().magnitude () / T{2})
+    { ; }
+
+
+    //-------------------------------------------------------------------------
+    template <typename T, typename B>
     hetero<T,B>::hetero(seed_t _seed,
                         unsigned _octaves,
                         T _H,