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from manimlib.imports import *
import numpy as np
def div(coordinate):
x,y = coordinate[:2]
return np.array([
x,
y,
0
])
class Loop(Scene):
def get_pending(self,path,proportion,dx=0.01):
if proportion < 1:
coord_i = path.point_from_proportion(proportion)
coord_f = path.point_from_proportion(proportion+dx)
else:
coord_i = path.point_from_proportion(proportion-dx)
coord_f = path.point_from_proportion(proportion)
line = Line(coord_i,coord_f)
angle = line.get_angle()
return angle
def construct(self):
boundary = VMobject(stroke_color = "#F4EDED")
boundary.set_points_smoothly([np.array([-2, 1.8,0]),np.array([-1.6, 0.5,0]),np.array([-3.2, -1.2,0]),np.array([2.6, -1.5,0]),np.array([1, 0,0]),np.array([3.5,2.3, 0]), np.array([-2,1.8, 0])])
#c = TexMobject(r"C").next_to(surf,RIGHT+UP).set_color("#F4EDED")
text = TexMobject(r"\oint \vec F \cdot \vec dr", r" = 0").shift(3*DOWN).set_stroke(width = 1.5)
vec_field = VectorField(div)
start_angle = self.get_pending(boundary, 0)
pointer = Triangle(fill_opacity = 1).set_height(0.25).set_color(WHITE)
pointer.set_fill(WHITE)
pointer.move_to(boundary.get_start())
pointer.rotate(- PI / 2)
pointer.save_state()
pointer.rotate(start_angle, about_point=pointer.get_center())
self.play(ShowCreation(boundary), ShowCreation(vec_field))
self.wait()
self.play(Write(text[0]))
def update_rotate_move(mob,alpha):
pointer.restore()
angle = self.get_pending(boundary,alpha)
pointer.move_to(boundary.point_from_proportion(alpha))
pointer.rotate(angle, about_point=pointer.get_center())
self.play(
#self.camera_frame.scale,.25,
UpdateFromAlphaFunc(pointer,update_rotate_move),
run_time=3,
)
self.play(ShowCreation(text[1]))
self.play(Indicate(text))
self.wait()
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