From 4afcac5b36009005bebf4ac1ff27b76649bf3939 Mon Sep 17 00:00:00 2001
From: out-of-pixel <s64705@htw-dresden.de>
Date: Sat, 29 Jun 2013 17:39:03 +0200
Subject: [PATCH] add function angle() returns the angle between a vector and
 the default rotation

---
 vector.lua | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/vector.lua b/vector.lua
index 9b028f5..3c9ed6b 100644
--- a/vector.lua
+++ b/vector.lua
@@ -135,6 +135,16 @@ function vector:rotated(phi)
 	return new(c * self.x - s * self.y, s * self.x + c * self.y)
 end
 
+function vector:angle()
+    local a = new(1,0)
+    local angle = math.acos((a*self)/(a:len()*self:len()))
+    if self.y < 0 then
+      return -angle
+    else
+      return angle
+     end
+end
+
 function vector:perpendicular()
 	return new(-self.y, self.x)
 end