Create a RangeSlider widget (#18829)

ianhi · web-flow · commit 79ae33af56a9 · 2020-12-28T22:07:59.000+01:00
* create RangeSlider widget

* Update comments and docstring for RangeSlider + SliderBase

* test vertical orientation of RangeSlider

Also add a test of the polygon points to make sure that the slider is being rendered correctly.
diff --git a/doc/users/next_whats_new/range_slider.rst b/doc/users/next_whats_new/range_slider.rst
@@ -0,0 +1,4 @@
+New RangeSlider widget
+----------------------
+`.widgets.RangeSlider` allows for creating a slider that defines
+a range rather than a single value.
diff --git a/examples/widgets/range_slider.py b/examples/widgets/range_slider.py
@@ -0,0 +1,68 @@
+"""
+======================================
+Thresholding an Image with RangeSlider
+======================================
+
+Using the RangeSlider widget to control the thresholding of an image.
+
+The RangeSlider widget can be used similarly to the `.widgets.Slider`
+widget. The major difference is that RangeSlider's ``val`` attribute
+is a tuple of floats ``(lower val, upper val)`` rather than a single float.
+"""
+
+import numpy as np
+import matplotlib.pyplot as plt
+from matplotlib.widgets import RangeSlider
+
+# generate a fake image
+np.random.seed(19680801)
+N = 128
+img = np.random.randn(N, N)
+
+fig, axs = plt.subplots(1, 2, figsize=(10, 5))
+plt.subplots_adjust(bottom=0.25)
+
+im = axs[0].imshow(img)
+axs[1].hist(img.flatten(), bins='auto')
+axs[1].set_title('Histogram of pixel intensities')
+
+# Create the RangeSlider
+slider_ax = plt.axes([0.20, 0.1, 0.60, 0.03])
+slider = RangeSlider(slider_ax, "Threshold", img.min(), img.max())
+
+# Create the Vertical lines on the histogram
+lower_limit_line = axs[1].axvline(slider.val[0], color='k')
+upper_limit_line = axs[1].axvline(slider.val[1], color='k')
+
+
+def update(val):
+    # The val passed to a callback by the RangeSlider will
+    # be a tuple of (min, max)
+
+    # Update the image's colormap
+    im.norm.vmin = val[0]
+    im.norm.vmax = val[1]
+
+    # Update the position of the vertical lines
+    lower_limit_line.set_xdata([val[0], val[0]])
+    upper_limit_line.set_xdata([val[1], val[1]])
+
+    # Redraw the figure to ensure it updates
+    fig.canvas.draw_idle()
+
+
+slider.on_changed(update)
+plt.show()
+
+#############################################################################
+#
+# ------------
+#
+# References
+# """"""""""
+#
+# The use of the following functions, methods, classes and modules is shown
+# in this example:
+
+import matplotlib
+matplotlib.widgets.RangeSlider
diff --git a/lib/matplotlib/tests/test_widgets.py b/lib/matplotlib/tests/test_widgets.py
@@ -298,6 +298,33 @@ def test_slider_horizontal_vertical():
     assert_allclose(box.bounds, [0, 0, 1, 10/24])
 
 
+@pytest.mark.parametrize("orientation", ["horizontal", "vertical"])
+def test_range_slider(orientation):
+    if orientation == "vertical":
+        idx = [1, 0, 3, 2]
+    else:
+        idx = [0, 1, 2, 3]
+
+    fig, ax = plt.subplots()
+
+    slider = widgets.RangeSlider(
+        ax=ax, label="", valmin=0.0, valmax=1.0, orientation=orientation
+    )
+    box = slider.poly.get_extents().transformed(ax.transAxes.inverted())
+    assert_allclose(box.get_points().flatten()[idx], [0.25, 0, 0.75, 1])
+
+    slider.set_val((0.2, 0.6))
+    assert_allclose(slider.val, (0.2, 0.6))
+    box = slider.poly.get_extents().transformed(ax.transAxes.inverted())
+    assert_allclose(box.get_points().flatten()[idx], [0.2, 0, 0.6, 1])
+
+    slider.set_val((0.2, 0.1))
+    assert_allclose(slider.val, (0.1, 0.2))
+
+    slider.set_val((-1, 10))
+    assert_allclose(slider.val, (0, 1))
+
+
 def check_polygon_selector(event_sequence, expected_result, selections_count):
     """
     Helper function to test Polygon Selector.
diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
