[FIXED] Ticks not updating with slider and only positve quadrand of a plot visible in matplotlib

Issue

I am trying to draw a simplified top-down perspective of a wing. I am using sliders to change the wingspan (b) and wing surface (S).

I am using matplotlib.patch.Polygon to draw it symmetrically from the 0,0 point. But only the positive quarter is visible and plot limits are not updating with sliders. x and y max ticks are stuck at 1 and 1. The goal is to see the whole wing in the center of the plot with ticks updating.

The code below is a modified showcase from: https://matplotlib.org/stable/gallery/widgets/slider_demo.html

code:

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

%matplotlib widget
# Define initial parameters
init_S = 50
init_b = 50

# Create the figure and the polygon that we will manipulate
fig, ax = plt.subplots()
ax.add_patch(Rectangle((-init_b/2, -(init_S/init_b)/2), init_b, init_S/init_b, alpha=0.4))
ax.set_xlabel('Wingspan [m]')
ax.set_xlabel('Chord [m]')

# adjust the main plot to make room for the sliders
fig.subplots_adjust(left=0.25, bottom=0.25)

# Make a horizontal slider to control the wingspan
axb = fig.add_axes([0.25, 0.1, 0.65, 0.03])
b_slider = Slider(axb, r"Wingspan [$m$]", 0.1, 50, init_b, orientation="horizontal")

# Make a vertically oriented slider to control the surface 
axsurf = fig.add_axes([0.1, 0.25, 0.0225, 0.63])
S_slider = Slider(axsurf, r"Surface [$m^2$]", 0.1, 50, init_S, orientation = "vertical")

# The function to be called anytime a slider's value changes
def update(val):
    ax.cla() # clear plot before update
    ax.add_patch(Rectangle((-b_slider.val/2, -(S_slider.val/b_slider.val)/2), b_slider.val, S_slider.val/b_slider.val, alpha=0.4))
    plt.autoscale()
    fig.canvas.draw_idle()

# register the update function with each slider
b_slider.on_changed(update)
S_slider.on_changed(update)

# Create a `matplotlib.widgets.Button` to reset the sliders to initial values.
resetax = fig.add_axes([0.8, 0.025, 0.1, 0.04])
button = Button(resetax, 'Reset', hovercolor='0.975')

def reset(event):
    S_slider.reset()
    b_slider.reset()
button.on_clicked(reset)

plt.autoscale()
plt.show()

Solution

Perhaps the simplest way to do so is to define a Polygon and plot it within an update function, then use interact from ipywidgets to make the sliders, where you can set the limits, steps and initial values of variables:

import matplotlib.pyplot as plt
from shapely.geometry import Polygon
from ipywidgets import *

def update(b, S):

    a = S/b
    polygon = Polygon([[-b/2, -a/2],
                       [b/2, -a/2],
                       [b/2, a/2],
                       [-b/2, a/2]])

    fig, ax = plt.subplots()
    ax.fill(*polygon.exterior.xy, alpha=0.4)
    ax.axis('equal')
    ax.set_xlabel('$x$ [m]')
    ax.set_ylabel('$y$ [m]')
    ax.set_title(f'wingspan = {b} m,   surface area = {S} m$^2$')
    plt.show()

interact(update,
         b=widgets.IntSlider(min=0, max=20, step=1, value=10),
         S=widgets.IntSlider(min=0, max=400, step=10, value=50))

Answered By - Jeff