Create example of slider snapping to values

ianhi · ianhi · commit ee8f9d0e7ada · 2020-11-07T22:47:51.000-05:00
diff --git a/examples/widgets/slider_snap_demo.py b/examples/widgets/slider_snap_demo.py
@@ -0,0 +1,67 @@
+"""
+==========================
+Slider Value Snapping Demo
+==========================
+
+You can snap slider values to a discrete values using 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
+
+t = np.arange(0.0, 1.0, 0.001)
+a0 = 5
+f0 = 3
+s = a0 * np.sin(2 * np.pi * f0 * t)
+
+fig, ax = plt.subplots()
+plt.subplots_adjust(bottom=0.25)
+l, = plt.plot(t, s, lw=2)
+
+slider_bkd_color = 'lightgoldenrodyellow'
+ax_freq = plt.axes([0.25, 0.1, 0.65, 0.03], facecolor=slider_bkd_color)
+ax_amp = plt.axes([0.25, 0.15, 0.65, 0.03], facecolor=slider_bkd_color)
+
+# define the values to use for snapping
+allowed_amplitudes = np.concatenate([np.linspace(.1, 5, 100), [6, 7, 8, 9]])
+
+# create the sliders
+samp = Slider(
+    ax_amp, "Amp", 0.1, 9.0,
+    valinit=a0, valstep=allowed_amplitudes,
+    color="green"
+)
+
+sfreq = Slider(
+    ax_freq, "Freq", 0, 10*np.pi,
+    valinit=2*np.pi, valstep=np.pi,
+    initcolor=None
+)
+# initcolor is set to None to remove the line marking the valinit position
+
+
+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)
+
+ax_reset = plt.axes([0.8, 0.025, 0.1, 0.04])
+button = Button(ax_reset, 'Reset', color=slider_bkd_color, hovercolor='0.975')
+
+
+def reset(event):
+    sfreq.reset()
+    samp.reset()
+button.on_clicked(reset)
+
+
+plt.show()
