Simple integration of Dart/Flutter and Python

julia.py

# https://matplotlib.org/matplotblog/posts/animated-fractals/
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation
import time

x_start, y_start = -2, -2  # an interesting region starts here
width, height = 4, 4  # for 4 units up and right
density_per_unit = 80  # how many pixles per unit

# real and imaginary axis
re = np.linspace(x_start, x_start + width, width * density_per_unit )
im = np.linspace(y_start, y_start + height, height * density_per_unit)


threshold = 10  # max allowed iterations
frames = 100000  # number of frames in the animation

# we represent c as c = r*cos(a) + i*r*sin(a) = r*e^{i*a}
r = 0.7885
a = np.linspace(0, 2*np.pi, round(frames/1000))

fig = plt.figure(figsize=(5, 5))  # instantiate a figure to draw
ax = plt.axes()  # create an axes object

def julia_quadratic(zx, zy, cx, cy, threshold):
    """Calculates whether the number z[0] = zx + i*zy with a constant c = x + i*y
    belongs to the Julia set. In order to belong, the sequence 
    z[i + 1] = z[i]**2 + c, must not diverge after 'threshold' number of steps.
    The sequence diverges if the absolute value of z[i+1] is greater than 4.
    
    :param float zx: the x component of z[0]
    :param float zy: the y component of z[0]
    :param float cx: the x component of the constant c
    :param float cy: the y component of the constant c
    :param int threshold: the number of iterations to considered it converged
    """
    # initial conditions
    z = complex(zx, zy)
    c = complex(cx, cy)
    
    for i in range(threshold):
        z = z**2 + c
        if abs(z) > 4.:  # it diverged
            return i
        
    return threshold - 1  # it didn't diverge

def animate(iter):
    start_time = time.time()  # start timing
    
    ax.clear()  # clear axes object
    ax.set_xticks([], [])  # clear x-axis ticks
    ax.set_yticks([], [])  # clear y-axis ticks

    iter = iter % 100
    
    X = np.empty((len(re), len(im)))  # the initial array-like image
    cx, cy = r * np.cos(a[iter]), r * np.sin(a[iter])  # the initial c number

    with open("io.txt", "w") as file:
        file.write(str(iter))
    
    # iterations for the given threshold
    for i in range(len(re)):
        for j in range(len(im)):
            X[i, j] = julia_quadratic(re[i], im[j], cx, cy, threshold)
    
    img = ax.imshow(X.T, interpolation="bicubic", cmap='magma')
    
    elapsed_time = time.time() - start_time
    print(f"\r{iter} : {round(elapsed_time * 1000, 2)} ms", end='', flush=True)
    
    return [img]

anim = animation.FuncAnimation(fig, animate, frames=frames, interval=50, blit=True)
plt.show()

main.dart

import 'dart:async';
import 'dart:io';

void main(List<String> args) async {
  var p = await Process.start('python3', ['julia.py']);

  _getUpdates(p);
}

void _getUpdates(Process p) {
  var stopped = false;

  p.exitCode.then((value) => stopped = true);

  Timer.periodic(Duration(milliseconds: 500), (timer) {
    var file = File('io.txt');
    if (!file.existsSync()) {
      return;
    }

    if (stopped) {
      print('DONE');
      timer.cancel();
      return;
    }

    var lines = file.readAsLinesSync();

    if (lines.isNotEmpty) {
      stdout.write('\rFrames rendered: ${lines.first} ');
    }
  });
}