classes ArcBetweenPoints, CurvedArrow, CurvedDoubleArrow

This makes it easier to draw arcs

topics/geometry.py

@@ -96,6 +96,47 @@ class Arc(VMobject):
         
         return self
 
+
+
+class ArcBetweenPoints(Arc):
+
+    def __init__(self, start_point, end_point, angle = TAU/4, **kwargs):
+        if angle == 0:
+            raise Exception("Arc with zero curve angle. Use Line instead.")
+
+        midpoint = 0.5 * (start_point + end_point)
+        distance_vector = end_point - start_point
+        normal_vector = np.array([-distance_vector[1], distance_vector[0],0])
+        distance = np.linalg.norm(normal_vector)
+        normal_vector /= distance
+        radius = distance/2 / np.sin(0.5 * angle)
+        l = distance/2 / np.tan(0.5 * angle)
+        arc_center = midpoint + l * normal_vector
+        w = start_point - arc_center
+        if w[0] != 0:
+            start_angle = np.arctan(w[1]/w[0])
+        else:
+            start_angle = np.pi/2
+
+        Arc.__init__(self, angle,
+            radius = radius,
+            start_angle = start_angle,
+            **kwargs)
+        self.move_arc_center_to(arc_center)
+
+class CurvedArrow(ArcBetweenPoints):
+
+    def __init__(self, start_point, end_point, angle = TAU/4, **kwargs):
+        ArcBetweenPoints.__init__(self, start_point, end_point, angle = TAU/4, **kwargs)
+        self.add_tip()
+
+class CurvedDoubleArrow(ArcBetweenPoints):
+
+    def __init__(self, start_point, end_point, angle = TAU/4, **kwargs):
+        ArcBetweenPoints.__init__(self, start_point, end_point, angle = TAU/4, **kwargs)
+        self.add_tip(at_start = True, at_end = True)
+
+
 class Circle(Arc):
     CONFIG = {
         "color" : RED,