allow not drawing the line marking initial slider position

ianhi · ianhi · commit 70ff4cd66e87 · 2020-10-30T15:39:45.000-04:00
diff --git a/examples/widgets/slider_snap_demo.py b/examples/widgets/slider_snap_demo.py
@@ -31,8 +31,12 @@
 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)
+samp = Slider(axamp, "Amp", 0.1, 10.0, valinit=a0, valstep=allowed_amplitudes)
+
+# set initcolor to None to remove the line marking the valinit position
+sfreq = Slider(
+    axfreq, "Freq", 0, 10 * np.pi, valinit=f0, valstep=np.pi, initcolor=None
+)
 
 
 def update(val):
diff --git a/lib/matplotlib/widgets.py b/lib/matplotlib/widgets.py
@@ -255,7 +255,7 @@ class Slider(AxesWidget):
     def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt=None,
                  closedmin=True, closedmax=True, slidermin=None,
                  slidermax=None, dragging=True, valstep=None,
-                 orientation='horizontal', **kwargs):
+                 orientation='horizontal', initcolor='r', **kwargs):
         """
         Parameters
         ----------
@@ -302,6 +302,10 @@ def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt=None,
         orientation : {'horizontal', 'vertical'}, default: 'horizontal'
             The orientation of the slider.
 
+        initcolor : color or None, default: 'r'
+            The color of the line drawn at the *valinit* position. If None
+            then no line marking the inital position will be drawn.
+
         Notes
         -----
         Additional kwargs are passed on to ``self.poly`` which is the
@@ -353,10 +357,12 @@ def __init__(self, ax, label, valmin, valmax, valinit=0.5, valfmt=None,
         self.valinit = valinit
         if orientation == 'vertical':
             self.poly = ax.axhspan(valmin, valinit, 0, 1, **kwargs)
-            self.hline = ax.axhline(valinit, 0, 1, color='r', lw=1)
+            if initcolor is not None:
+                self.hline = ax.axhline(valinit, 0, 1, color=initcolor, lw=1)
         else:
             self.poly = ax.axvspan(valmin, valinit, 0, 1, **kwargs)
-            self.vline = ax.axvline(valinit, 0, 1, color='r', lw=1)
+            if initcolor is not None:
+                self.vline = ax.axvline(valinit, 0, 1, color=initcolor, lw=1)
 
         if orientation == 'vertical':
             ax.set_ylim((valmin, valmax))
