From 0d0e56fd830488d9bc6fd7fdc8d2e1a3fd9a7668 Mon Sep 17 00:00:00 2001
From: Grant Sanderson <grantsanderson7@gmail.com>
Date: Thu, 31 Dec 2015 09:24:02 -0800
Subject: [PATCH] Arrow can take one arg

---
 topics/geometry.py | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/topics/geometry.py b/topics/geometry.py
index 1668a467..f5c5030a 100644
--- a/topics/geometry.py
+++ b/topics/geometry.py
@@ -38,7 +38,7 @@ class Cross(Mobject1D):
 
 class Line(Mobject1D):
     DEFAULT_CONFIG = {
-        "buffer" : 0
+        "buff" : 0
     }
     def __init__(self, start, end, **kwargs):
         digest_config(self, kwargs)
@@ -64,8 +64,8 @@ class Line(Mobject1D):
         ]
         start_to_end = self.end - self.start
         start_to_end /= np.linalg.norm(start_to_end)
-        self.start = self.start + self.buffer*start_to_end
-        self.end = self.end - self.buffer*start_to_end
+        self.start = self.start + self.buff*start_to_end
+        self.end = self.end - self.buff*start_to_end
 
     def generate_points(self):
         self.add_line(self.start, self.end)
@@ -84,9 +84,16 @@ class Arrow(Line):
     DEFAULT_CONFIG = {
         "color"      : YELLOW_C,
         "tip_length" : 0.25,
-        "buffer"     : 0.3,
+        "buff"       : 0.3,
     }
     def __init__(self, *args, **kwargs):
+        if len(args) == 1:
+            target = args[0]
+            if isinstance(target, Mobject):
+                point = target.get_center()
+            else:
+                point = target
+            args = (point+UP+LEFT, target)
         Line.__init__(self, *args, **kwargs)
         self.add_tip()