Created
January 17, 2021 23:54
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A manim scene for drawing stuff with epicycles using Fourier shenanigans
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import random | |
import numpy as np | |
import manim as mn | |
from svg.path import parse_path | |
def integrate(func, a, b, *, dx=0.01): | |
return sum(func(x) * dx for x in np.arange(a, b, dx)) | |
class SVGPath(mn.VMobject): | |
def __init__(self, path_str, *, num_points=500, **kwargs): | |
self.path = parse_path(path_str) | |
self.num_points = num_points | |
super().__init__(**kwargs) | |
def point(self, alpha): | |
z = self.path.point(alpha) | |
return np.array([z.real, z.imag, 0]) | |
def generate_points(self): | |
step = 1 / self.num_points | |
points = [self.point(x) for x in np.arange(0, 1, step)] | |
self.start_new_path(points[0]) | |
self.add_points_as_corners(points[1:]) | |
self.add_line_to(self.point(1)) | |
self.flip(mn.RIGHT) | |
self.center() | |
return self | |
class Epicycle(mn.VMobject): | |
def __init__(self, path, coeff_start, coeff_end=None, *, num_points=500, **kwargs): | |
self.num_points = num_points | |
if coeff_end is None: | |
coeff_end = int(np.ceil(coeff_start / 2)) | |
coeff_start = coeff_end - coeff_start | |
self.coeffs = self.gen_fourier_coeffs(path, coeff_start, coeff_end) | |
super().__init__(**kwargs) | |
def generate_points(self): | |
step = 1 / self.num_points | |
points = [self.point(x) for x in np.arange(0, 1, step)] | |
self.start_new_path(points[0]) | |
self.add_points_as_corners(points[1:]) | |
self.add_line_to(points[0]) | |
return self | |
def point(self, alpha): | |
z = sum(radius * np.exp(alpha * speed * mn.TAU * 1j) for speed, radius in self.coeffs.items()) | |
return np.array([z.real, z.imag, 0]) | |
def gen_fourier_coeffs(self, path, start, end): | |
def point(alpha): | |
pt = path.point_from_proportion(alpha) - path.get_center() | |
return complex(pt[0], pt[1]) | |
# speed: radius | |
return {i: integrate(lambda x: point(x) * np.exp(x * -i * mn.TAU * 1j), 0, 1) for i in range(start, end)} | |
def draw_circles(self, alpha, whole_mobject=None, **kwargs): | |
if whole_mobject is None: | |
whole_mobject = self.copy() | |
self.submobjects.clear() | |
self.pointwise_become_partial(whole_mobject, 0, alpha) | |
speeds_and_radii = sorted(self.coeffs.items(), key=lambda x: abs(x[1]), reverse=True) | |
z = 0 | |
for speed, radius in speeds_and_radii: | |
circ = mn.Circle(**kwargs) | |
circ.scale(abs(radius)) | |
circ.move_to([z.real, z.imag, 0]) | |
self.add(circ) | |
z += radius * np.exp(alpha * speed * mn.TAU * 1j) | |
return self | |
def animate_circles(self, **kwargs): | |
class Draw(mn.Animation): | |
def interpolate_submobject(self, submobject, starting_submobject, alpha): | |
submobject.draw_circles(alpha, starting_submobject, **kwargs) | |
return Draw(self) | |
class EpicCycle(mn.Scene): | |
path_str = "M 2.614456,0.04305907 C -0.03519642,-0.05013041 0.29631932,2.7704015 0.38598443,2.8585255 L 1.2958347,1.8249996 1.1244138,1.2725989 1.2958347,1.8249996 2.2979871,0.55982315 1.7046078,1.3795156 2.1397537,1.3438767 1.7046078,1.3795156 -0.00960316,3.482204 0.1090739,3.678218 0.5969637,3.0010812 c 0.0566946,0.085227 -0.0821144,-0.036163 0,0 1.896299,0.8350973 2.1009769,-2.94190352 2.0174923,-2.95802213 z" | |
def construct(self): | |
# Scale because I don't want to edit the SVG because I'm lazy | |
path = SVGPath(self.path_str).scale(1.75) | |
path.set_color(mn.RED).set_opacity(0.5) | |
self.add(path) | |
for num_coeffs in range(5, 105 + 1, 20): | |
ep = Epicycle(path, num_coeffs) | |
ep_copy = ep.copy().draw_circles(0, color=mn.BLUE) | |
text = mn.Tex(f"Cycles: {num_coeffs}").to_edge(mn.UP).shift(mn.LEFT) | |
self.play(mn.FadeIn(mn.VGroup(ep_copy, text)), run_time=0.75) | |
self.remove(ep_copy) | |
self.play(ep.animate_circles(color=mn.BLUE), run_time=10, rate_func=mn.linear) | |
self.play(mn.FadeOut(mn.VGroup(ep, text))) |
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hello, i am looking for a way to hide the blue circles that trace the path. i've tried using .set_opacity(0) at multiples places but it doesnt seem to work. i'd be thankful if you could help me out with it.