Interactive circle transformation via matrix multiplication

interactive_circle_transformation.py

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.widgets import Slider

fig, ax = plt.subplots()

fig.tight_layout()
ax.set_aspect('equal', adjustable='box')
ax.set_frame_on(False)

# Cirlce matrix with 2x100 shape
theta = np.linspace(0, 3 * np.pi, 120)
radius = 32

# Plot the circle
def plot_circle(c, style='.'):
    ax.plot(c[:, 0], c[:, 1], style)

c = np.stack((radius * np.cos(theta), radius*np.sin(theta))).T
plot_circle(c)

# Set min and max slider vals
val_min = -32
val_max = 32

# Make room for slider
plt.subplots_adjust(bottom=0.35)

# Make sliders
ax_x1 = plt.axes([0.25, 0.2, 0.65, 0.03])
x1_slider = Slider(
    ax=ax_x1,
    label="x1",
    valmin=val_min,
    valmax=val_max,
    valinit=1,
)

ax_y1 = plt.axes([0.25, 0.15, 0.65, 0.03])
y1_slider = Slider(
    ax=ax_y1,
    label="y1",
    valmin=val_min,
    valmax=val_max,
    valinit=0,
)

ax_x2 = plt.axes([0.25, 0.1, 0.65, 0.03])
x2_slider = Slider(
    ax=ax_x2,
    label="x2",
    valmin=val_min,
    valmax=val_max,
    valinit=0,
)

ax_y2 = plt.axes([0.25, 0.05, 0.65, 0.03])
y2_slider = Slider(
    ax=ax_y2,
    label="y2",
    valmin=val_min,
    valmax=val_max,
    valinit=1,
)

def on_changed(val):
    T = np.array([
        [x1_slider.val, y1_slider.val],
        [x2_slider.val, y2_slider.val],
    ])

    c = np.stack((radius * np.cos(theta), radius*np.sin(theta))).T
    cT = c@T

    ax.clear()
    plot_circle(c, '-')
    plot_circle(cT, 'g+')


x1_slider.on_changed(on_changed)
y1_slider.on_changed(on_changed)

x2_slider.on_changed(on_changed)
y2_slider.on_changed(on_changed)

plt.legend()
plt.show()