Create example of slider snapping to values

ianhi · ianhi · commit 822c3c75109b · 2020-10-30T15:37:56.000-04:00
diff --git a/examples/widgets/slider_snap_demo.py b/examples/widgets/slider_snap_demo.py
@@ -0,0 +1,58 @@
+"""
+==========================
+Slider Value Snapping Demo
+==========================
+
+You can snap slider values to a discrete values using either the ``valstep``
+argument. 
+
+In this example the Freq slider is constrained to be multiples of pi, and the
+Amp slider uses an array as the ``valstep`` argument to more densely sample
+the first part of its range.
+"""
+import numpy as np
+import matplotlib.pyplot as plt
+from matplotlib.widgets import Slider, Button
+
+fig, ax = plt.subplots()
+plt.subplots_adjust(bottom=0.25)
+t = np.arange(0.0, 1.0, 0.001)
+a0 = 5
+f0 = 3
+s = a0 * np.sin(2 * np.pi * f0 * t)
+l, = plt.plot(t, s, lw=2)
+
+axcolor = 'lightgoldenrodyellow'
+axfreq = plt.axes([0.25, 0.1, 0.65, 0.03], facecolor=axcolor)
+axamp = plt.axes([0.25, 0.15, 0.65, 0.03], facecolor=axcolor)
+
+# define the values to use for snapping
+delta_f = np.pi
+allowed_amplitudes = np.concatenate([np.linspace(.1, 5, 100), [7, 8, 9, 10]])
+
+# create the sliders
+samp = Slider(axamp, 'Amp', 0.1, 10.0, valinit=a0, valstep=allowed_amplitudes)
+sfreq = Slider(axfreq, 'Freq', 0, 10*np.pi, valinit=f0, valstep=np.pi)
+
+
+def update(val):
+    amp = samp.val
+    freq = sfreq.val
+    l.set_ydata(amp*np.sin(2*np.pi*freq*t))
+    fig.canvas.draw_idle()
+
+
+sfreq.on_changed(update)
+samp.on_changed(update)
+
+resetax = plt.axes([0.8, 0.025, 0.1, 0.04])
+button = Button(resetax, 'Reset', color=axcolor, hovercolor='0.975')
+
+
+def reset(event):
+    sfreq.reset()
+    samp.reset()
+button.on_clicked(reset)
+
+
+plt.show()
