From 9c63070718d8b9ec3e019e538e3cfa367fcd6fea Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Wed, 4 Jan 2012 17:08:03 +1100
Subject: [PATCH] Add various interpolation routines for perlin

---
 Makefile.am |  2 ++
 lerp.cpp    | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 lerp.hpp    | 30 ++++++++++++++++++++++++++++++
 3 files changed, 81 insertions(+)
 create mode 100644 lerp.cpp
 create mode 100644 lerp.hpp

diff --git a/Makefile.am b/Makefile.am
index d4d5174a..362fa271 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -44,6 +44,8 @@ UTIL_FILES   =		\
     ip.hpp		\
     json.cpp		\
     json.hpp		\
+    lerp.cpp		\
+    lerp.hpp		\
     maths.cpp		\
     maths.hpp		\
     maths/matrix.cpp	\
diff --git a/lerp.cpp b/lerp.cpp
new file mode 100644
index 00000000..0e629f12
--- /dev/null
+++ b/lerp.cpp
@@ -0,0 +1,49 @@
+/*
+ * This file is part of libgim.
+ *
+ * libgim is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later
+ * version.
+ *
+ * libgim is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with libgim.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Copyright 2011 Danny Robson <danny@blubinc.net>
+ */
+
+#include "lerp.hpp"
+
+#include "debug.hpp"
+#include "maths.hpp"
+
+#include <cmath>
+
+
+double
+lerp::sigmoid (double val) {
+    return -1.0 + 2.0 / (1.0 + exp (-2.0 * val));
+}
+
+
+double
+lerp::linear (double a, double b, double weight) {
+    check (weight >= 0 && weight <= 1.0);
+    return (1.0 - weight) * a + weight * b;
+}
+
+
+double
+lerp::cosine (double a, double b, double weight) {
+    check (weight >= 0 && weight <= 1.0);
+    double ft = weight * PI;
+    double f  = (1.0 - cos (ft)) * 0.5;
+
+    return a * (1.0 - f) + b * f;
+}
+
diff --git a/lerp.hpp b/lerp.hpp
new file mode 100644
index 00000000..145e8bc4
--- /dev/null
+++ b/lerp.hpp
@@ -0,0 +1,30 @@
+/*
+ * This file is part of libgim.
+ *
+ * libgim is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later
+ * version.
+ *
+ * libgim is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with libgim.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Copyright 2011 Danny Robson <danny@blubinc.net>
+ */
+
+#ifndef __UTIL_LERP_HPP
+#define __UTIL_LERP_HPP
+
+namespace lerp {
+    double sigmoid (double val);
+
+    double linear (double a, double b, double weight);
+    double cosine (double a, double b, double weight);
+}
+
+#endif