added interface for walkers

some new helper methods
added interpolater for paths

math/Interpolator.h

@@ -0,0 +1,52 @@
+#ifndef INTERPOLATOR_H
+#define INTERPOLATOR_H
+
+#include "../Assertions.h"
+
+/**
+ * interpolate between two adjacent values based on their key
+ */
+template <typename Key, typename Value> class Interpolator {
+
+public:
+
+	/** value at key */
+	struct Entry {
+		Key key;
+		Value value;
+		Entry(const Key key, const Value& pos) : key(key), value(value) {;}
+	};
+
+protected:
+
+	/** all added entries, SORTED by their key */
+	std::vector<Entry> entries;
+
+public:
+
+	/** add a new value with its key. entries must be added in sorted order! */
+	void add(const Key key, const Value& value) {
+		Assert::isTrue (entries.empty() || entries.back().key < key, "entries must be ordered!");
+		entries.push_back(Entry(key, value));
+	}
+
+	/** get the interpolated value for the given key */
+	Value get(const Key key) const {
+		const int idx1 = getIdx(key);
+		const int idx2 = idx1+1;
+		const float percent = (key - entries[idx1].key) / (float) (entries[idx2].key - entries[idx1].key);
+		return entries[idx1].value + (entries[idx2].value - entries[idx1].value) * percent;
+	}
+
+	/** get the nearest index for the given key */
+	int getIdx(const Key key) const {
+		// TODO: use O(log(n)) search here!
+		for (size_t i = 0; i < entries.size(); ++i) {
+			if (entries[i].key > key) {return i-1;}
+		}
+		throw "should not happen";
+	}
+
+};
+
+#endif // INTERPOLATOR_H