From 2afd89dbf3664d8c1564cc7627e3085a53e3a842 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?R=C3=A9mi=20Oudin?= <oudin@crans.org>
Date: Tue, 13 Feb 2018 23:38:24 +0100
Subject: [PATCH] Fractional Brownian Motion

---
 PerlinNoise.cpp | 17 ++++++++++++++++-
 PerlinNoise.hpp |  2 ++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/PerlinNoise.cpp b/PerlinNoise.cpp
index b649bf9..059d86d 100644
--- a/PerlinNoise.cpp
+++ b/PerlinNoise.cpp
@@ -44,7 +44,7 @@ PerlinNoise::PerlinNoise(unsigned int seed) : ImplicitSurface(Point(0,0,0)) {
 }
 
 double PerlinNoise::operator() (double x, double y, double z) const {
-    return z - noise(x, 0, y);
+    return z - fBm(x, 0, y, 2, 0.3, 2.0);
 }
 
 double PerlinNoise::noise(double _x, double _y, double _z) const {
@@ -111,6 +111,21 @@ double PerlinNoise::grad(int hash, double x, double y, double z)  const {
 	return ((h & 1) == 0 ? u : -u) + ((h & 2) == 0 ? v : -v);
 }
 
+double PerlinNoise::fBm(double x, double y, double z, int octaves, double
+        lacunarity, double gain) const {
+    double amplitude = 1.0;
+    double frequency = 1.0;
+    double sum = 0.0;
+    for(int i = 0; i < octaves; ++i)
+    {
+//        sum += amplitude * (1-abs(noise(x * frequency, y * frequency, z * frequency)));
+        sum += amplitude * noise(x * frequency, y * frequency, z * frequency);
+        amplitude *= gain;
+        frequency *= lacunarity;
+    }
+    return sum;
+}
+
 Point PerlinNoise::normal_vector(double x, double y) {
     double n_x_y = noise(x, y, 0);
     double n_dx_y = noise(x + 0.01, y, 0);
diff --git a/PerlinNoise.hpp b/PerlinNoise.hpp
index 00e613c..47bc41b 100644
--- a/PerlinNoise.hpp
+++ b/PerlinNoise.hpp
@@ -16,6 +16,8 @@ class PerlinNoise : public ImplicitSurface {
         double operator() (double _x, double _y, double _z) const;
         double noise(double x, double y) const;
         Point normal_vector(double x, double y);
+        double fBm(double x, double y, double z, int octaves, double
+                lacunarity, double gain) const;
 
         virtual Point location_hint() const;
         Point location_hint(double x, double z) const;