add interactive colorbar example to gallery (matplotlib#20471)

* add interactive colorbar example to gallery

Author: richardsheridan

examples/userdemo/colormap_interactive_adjustment.py

@@ -0,0 +1,90 @@
+"""
+========================================
+Interactive Adjustment of Colormap Range
+========================================
+
+Demonstration of using colorbar, picker, and event functionality to make an
+interactively adjustable colorbar widget.
+
+Left clicks and drags inside the colorbar axes adjust the high range of the
+color scheme. Likewise, right clicks and drags adjust the low range. The
+connected AxesImage immediately updates to reflect the change.
+"""
+
+import numpy as np
+import matplotlib.pyplot as plt
+from matplotlib.backend_bases import MouseButton
+
+###############################################################################
+# Callback definitions
+
+
+def on_pick(event):
+    adjust_colorbar(event.mouseevent)
+
+
+def on_move(mouseevent):
+    if mouseevent.inaxes is colorbar.ax:
+        adjust_colorbar(mouseevent)
+
+
+def adjust_colorbar(mouseevent):
+    if mouseevent.button == MouseButton.LEFT:
+        colorbar.norm.vmax = max(mouseevent.ydata, colorbar.norm.vmin)
+    elif mouseevent.button == MouseButton.RIGHT:
+        colorbar.norm.vmin = min(mouseevent.ydata, colorbar.norm.vmax)
+    else:
+        # discard all others
+        return
+
+    canvas.draw_idle()
+
+
+###############################################################################
+# Generate figure with Axesimage and Colorbar
+
+fig, ax = plt.subplots()
+canvas = fig.canvas
+
+delta = 0.1
+x = np.arange(-3.0, 4.001, delta)
+y = np.arange(-4.0, 3.001, delta)
+X, Y = np.meshgrid(x, y)
+Z1 = np.exp(-X**2 - Y**2)
+Z2 = np.exp(-(X - 1)**2 - (Y - 1)**2)
+Z = (0.9*Z1 - 0.5*Z2) * 2
+
+cmap = plt.get_cmap('viridis').with_extremes(
+    over='xkcd:orange', under='xkcd:dark red')
+axesimage = plt.imshow(Z, cmap=cmap)
+colorbar = plt.colorbar(axesimage, ax=ax, use_gridspec=True)
+
+###############################################################################
+# Note that axesimage and colorbar share a Normalize object
+# so they will stay in sync
+
+assert colorbar.norm is axesimage.norm
+colorbar.norm.vmax = 1.5
+axesimage.norm.vmin = -0.75
+
+###############################################################################
+# Hook Colorbar up to canvas events
+
+# `set_navigate` helps you see what value you are about to set the range
+# to, and enables zoom and pan in the colorbar which can be helpful for
+# narrow or wide data ranges
+colorbar.ax.set_navigate(True)
+
+# React to all motion with left or right mouse buttons held
+canvas.mpl_connect("motion_notify_event", on_move)
+
+# React only to left and right clicks
+colorbar.ax.set_picker(True)
+canvas.mpl_connect("pick_event", on_pick)
+
+###############################################################################
+# Display
+#
+# The colormap will now respond to left and right clicks in the Colorbar axes
+
+plt.show()