FIX force vmin/vmax to 0/1 whenever an array is passed as alpha (#461)

* FIX force vmin/vmax to 0/1 whenever an array is passed as alpha

* Add warning if alpha values are outside [0, 1]

cortex/dataset/viewRGB.py

@@ -1,5 +1,6 @@
 import numpy as np
 import colorsys
+import warnings
 
 from .views import Dataview, Volume, Vertex
 from .braindata import VolumeData, VertexData, _hash
@@ -256,7 +257,14 @@ def alpha(self):
             alpha = np.ones(self.red.volume.shape)
             alpha = Volume(alpha, self.red.subject, self.red.xfmname, vmin=0, vmax=1)
         if not isinstance(alpha, Volume):
-            alpha = Volume(alpha, self.red.subject, self.red.xfmname)
+            if alpha.min() < 0 or alpha.max() > 1:
+                warnings.warn(
+                    "Some alpha values are outside the range of [0, 1]. "
+                    "Consider passing a Volume object as alpha with explicit vmin, vmax "
+                    "keyword arguments.",
+                    Warning
+                )
+            alpha = Volume(alpha, self.red.subject, self.red.xfmname, vmin=0, vmax=1)
 
         rgb = np.array([self.red.volume, self.green.volume, self.blue.volume])
         mask = np.isnan(rgb).any(axis=0)
@@ -523,7 +531,14 @@ def alpha(self):
             alpha = np.ones(self.red.vertices.shape[1])
             alpha = Vertex(alpha, self.red.subject, vmin=0, vmax=1)
         if not isinstance(alpha, Vertex):
-            alpha = Vertex(alpha, self.red.subject)
+            if alpha.min() < 0 or alpha.max() > 1:
+                warnings.warn(
+                    "Some alpha values are outside the range of [0, 1]. "
+                    "Consider passing a Vertex object as alpha with explicit vmin, vmax "
+                    "keyword arguments.",
+                    Warning
+                )
+            alpha = Vertex(alpha, self.red.subject, vmin=0, vmax=1)
 
         rgb = np.array([self.red.data, self.green.data, self.blue.data])
         mask = np.isnan(rgb).any(axis=0)