Implement listener, emitter, and -3dB pan law

lib/Listener.cpp

@@ -0,0 +1,39 @@
+#include "amuse/Listener.hpp"
+
+namespace amuse
+{
+
+static void Cross(Vector3f& out, const Vector3f& a, const Vector3f& b)
+{
+    out[0] = a[1] * b[2] - a[2] * b[1];
+    out[1] = a[2] * b[0] - a[0] * b[2];
+    out[2] = a[0] * b[1] - a[1] * b[0];
+}
+
+static float Normalize(Vector3f& out)
+{
+    float dist = Length(out);
+    if (dist == 0.f)
+        return 0.f;
+    out[0] /= dist;
+    out[1] /= dist;
+    out[2] /= dist;
+    return dist;
+}
+
+void Listener::setVectors(const float* pos, const float* dir, const float* heading, const float* up)
+{
+    for (int i=0 ; i<3 ; ++i)
+    {
+        m_pos[i] = pos[i];
+        m_dir[i] = dir[i];
+        m_heading[i] = heading[i];
+        m_up[i] = up[i];
+    }
+    Normalize(m_heading);
+    Normalize(m_up);
+    Cross(m_right, m_heading, m_up);
+    Normalize(m_right);
+}
+
+}