TextBox improvements.

anntzer · anntzer · commit b833a2b471b2 · 2020-04-13T18:26:05.000+02:00
Cleanup textbox example: 1) handling the initial text through the normal
`submit` callback seems simpler; 2) use "normal" autoscaling methods,
which correctly apply margins and would also work if other artists were
involved.  This revealed that `TextBox.set_val` throws an exception due
to no cached renderer if the figure has never been rendered before.
Given that TextBox is going to trigger a bunch of redraws anyways for
user edits, we may as well trigger a first draw if needed to cache a
renderer first.
diff --git a/examples/widgets/textbox.py b/examples/widgets/textbox.py
@@ -16,12 +16,13 @@
 import numpy as np
 import matplotlib.pyplot as plt
 from matplotlib.widgets import TextBox
+
+
 fig, ax = plt.subplots()
-plt.subplots_adjust(bottom=0.2)
+fig.subplots_adjust(bottom=0.2)
+
 t = np.arange(-2.0, 2.0, 0.001)
-s = t ** 2
-initial_text = "t ** 2"
-l, = plt.plot(t, s, lw=2)  # make a plot for the math expression "t ** 2"
+l, = ax.plot(t, np.zeros_like(t), lw=2)
 
 
 def submit(expression):
@@ -33,12 +34,15 @@ def submit(expression):
     """
     ydata = eval(expression)
     l.set_ydata(ydata)
-    ax.set_ylim(np.min(ydata), np.max(ydata))
+    ax.relim()
+    ax.autoscale_view()
     plt.draw()
 
-axbox = plt.axes([0.1, 0.05, 0.8, 0.075])
-text_box = TextBox(axbox, 'Evaluate', initial=initial_text)
+
+axbox = fig.add_axes([0.1, 0.05, 0.8, 0.075])
+text_box = TextBox(axbox, "Evaluate")
 text_box.on_submit(submit)
+text_box.set_val("t ** 2")  # Trigger `submit` with the initial string.
 
 plt.show()
 
diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
@@ -767,6 +767,12 @@ def _rendercursor(self):
         # and save its dimensions, draw the real text, then put the cursor
         # at the saved dimensions
 
+        # This causes a single extra draw if the figure has never been rendered
+        # yet, which should be fine as we're going to repeatedly re-render the
+        # figure later anyways.
+        if self.ax.figure._cachedRenderer is None:
+            self.ax.figure.canvas.draw()
+
         text = self.text_disp.get_text()  # Save value before overwriting it.
         widthtext = text[:self.cursor_index]
         self.text_disp.set_text(widthtext or ",")
