Factored out Line.get_start and Line.get_end to be more general Mobject methods

manimlib/mobject/geometry.py

@@ -327,37 +327,17 @@ class Line(VMobject):
         else:
             return self.get_length()
 
-    def get_start_and_end(self):
-        return self.get_start(), self.get_end()
-
     def get_vector(self):
         return self.get_end() - self.get_start()
 
     def get_unit_vector(self):
-        vect = self.get_vector()
-        norm = get_norm(vect)
-        if norm == 0:
-            # TODO, is this the behavior I want?
-            return np.array(ORIGIN)
-        return vect / norm
-
-    def get_start(self):
-        return np.array(self.points[0])
-
-    def get_end(self):
-        return np.array(self.points[-1])
-
-    def get_slope(self):
-        start, end = self.get_start_and_end()
-        rise, run = [
-            float(end[i] - start[i])
-            for i in [1, 0]
-        ]
-        return np.inf if run == 0 else rise / run
+        return normalize(self.get_vector())
 
     def get_angle(self):
-        start, end = self.get_start_and_end()
-        return angle_of_vector(end - start)
+        return angle_of_vector(self.get_vector())
+
+    def get_slope(self):
+        return np.tan(self.get_angle())
 
     def set_angle(self, angle):
         self.rotate(

manimlib/mobject/mobject.py

@@ -535,8 +535,20 @@ class Mobject(Container):
         self.scale_in_place((length + buff) / length)
         return self
 
+    def get_start(self):
+        self.throw_error_if_no_points()
+        return np.array(self.points[0])
+
+    def get_end(self):
+        self.throw_error_if_no_points()
+        return np.array(self.points[-1])
+
+    def get_start_and_end(self):
+        return self.get_start(), self.get_end()
+
     def put_start_and_end_on(self, start, end):
-        curr_vect = self.points[-1] - self.points[0]
+        curr_start, curr_end = self.get_start_and_end()
+        curr_vect = curr_end - curr_start
         if np.all(curr_vect == 0):
             raise Exception("Cannot position endpoints of closed loop")
         target_vect = end - start
@@ -545,7 +557,7 @@ class Mobject(Container):
             angle_of_vector(target_vect) -
             angle_of_vector(curr_vect)
         )
-        self.shift(start - self.points[0])
+        self.shift(start - self.get_start())
         return self
 
     # Background rectangle
@@ -1032,6 +1044,17 @@ class Mobject(Container):
             sm1.interpolate_color(sm1, sm2, 1)
         return self
 
+    # Errors
+    def has_no_points(self):
+        return len(self.points) == 0
+
+    def throw_error_if_no_points(self):
+        if self.has_no_points():
+            message = "Cannot call Mobject.{}" +\
+                      "for a Mobject with no points"
+            caller_name = sys._getframe(1).f_code.co_name
+            raise Exception(message.format(caller_name))
+
 
 class Group(Mobject):
     def __init__(self, *mobjects, **kwargs):

manimlib/mobject/types/vectorized_mobject.py

@@ -472,9 +472,6 @@ class VMobject(Mobject):
             self.points[0], self.points[-1]
         )
 
-    def has_no_points(self):
-        return len(self.points) == 0
-
     def add_points_as_corners(self, points):
         for point in points:
             self.add_line_to(point)
@@ -791,14 +788,6 @@ class VMobject(Mobject):
             ))
         return self
 
-    # Errors
-    def throw_error_if_no_points(self):
-        if self.has_no_points():
-            message = "Cannot call VMobject.{}" +\
-                      "for a VMobject with no points"
-            caller_name = sys._getframe(1).f_code.co_name
-            raise Exception(message.format(caller_name))
-
 
 class VGroup(VMobject):
     def __init__(self, *vmobjects, **kwargs):