flexibility to return with alpha channel and/or as string

python/damask/_colormap.py

@@ -193,25 +193,39 @@ class Colormap(mpl.colors.ListedColormap):
 
 
     def at(self,
-           fraction : float) -> np.ndarray:
+           fraction : Union[float,Sequence[float]],
+           with_alpha : bool = False,
+           as_string : bool = False) -> np.ndarray:
         """
         Interpolate color at fraction.
 
         Parameters
         ----------
-        fraction : float
-            Fractional coordinate to evaluate Colormap at.
+        fraction : float or sequence of float
+            Fractional coordinate(s) to evaluate Colormap at.
+        with_alpha : bool
+            Provide opacity as fourth value.
+        as_string : bool
+            Encode color as 'rgb(r,g,b)' or 'rgba(r,g,b,a)'.
 
         Returns
         -------
-        color : np.ndarray, shape(3)
-            RGB values of interpolated color.
+        color : np.ndarray, shape(3 or 4), or string
+            RGB(A) values of interpolated color.
 
         """
-        return interp.interp1d(np.linspace(0,1,self.N),
-                               self.colors,
-                               axis=0,
-                               assume_sorted=True)(fraction)
+        def _stringify(color):
+            d = color.shape[-1]
+            c = np.array([f'rgba({c[0]},{c[1]},{c[2]},{c[3]})' if d==4
+                     else f'rgb({c[0]},{c[1]},{c[2]})' for c in np.atleast_2d(color)])
+            return c if len(c)>1 else c[0]
+
+
+        color = interp.interp1d(np.linspace(0,1,self.N),
+                                self.colors,
+                                axis=0,
+                                assume_sorted=True)(fraction)[...,:4 if with_alpha else 3]
+        return _stringify(color) if as_string else color
 
 
     def shade(self,

python/tests/test_Colormap.py

@@ -139,12 +139,23 @@ class TestColormap:
         c += c
         assert (np.allclose(c.colors[:len(c.colors)//2],c.colors[len(c.colors)//2:]))
 
-    @pytest.mark.parametrize('N,cmap',[
-                                       (8,'gray'),
-                                       (17,'gray'),
-                                      ])
-    def test_at(self, N, cmap):
-        assert np.allclose(Colormap.from_predefined(cmap,N=N).at(0.5)[:3],0.5,rtol=0.005)
+    @pytest.mark.parametrize('N,cmap,at,with_alpha,result',[
+           (8,'gray',0.5,False,[0.5,0.5,0.5]),
+           (17,'gray',0.5,False,[0.5,0.5,0.5]),
+           (17,'gray',[0.5,0.75],False,[[0.5,0.5,0.5],[0.75,0.75,0.75]]),
+           ])
+    def test_at_value(self, N, cmap, at, with_alpha, result):
+        assert np.allclose(Colormap.from_predefined(cmap,N=N).at(at,with_alpha=with_alpha),
+                           result,
+                           rtol=0.005)
+
+    @pytest.mark.parametrize('N,cmap,at,with_alpha,result',[
+           (8,'gray',0.5,False,'rgb(0.5,0.5,0.5)'),
+           (8,'gray',0.5,True,'rgba(0.5,0.5,0.5,1.0)'),
+           (8,'gray',[0.5,0.25],True,['rgba(0.5,0.5,0.5,1.0)','rgba(0.25,0.25,0.25,1.0)']),
+           ])
+    def test_at_string(self, N, cmap, at, with_alpha, result):
+        assert np.all(Colormap.from_predefined(cmap,N=N).at(at,with_alpha=with_alpha,as_string=True) == result)
 
     @pytest.mark.parametrize('bounds',[None,[2,10]])
     def test_shade(self,ref_path,update,bounds):