Add the possibility to pass the color as a float if the user wants to…

… specify just the alpha channel in meshcat_visualizer.py

bindings/python/visualize/meshcat_visualizer.py

@@ -159,7 +159,7 @@ def __primitive_geometry_exists(self, geometry_name: str):
         return geometry_name in self.primitive_geometries_names
 
     def __add_model_geometry_to_viewer(
-        self, model_geometry: idyn.ModelSolidShapes, model_name: str, color: list
+        self, model_geometry: idyn.ModelSolidShapes, model_name: str, color
     ):
         import meshcat
 
@@ -226,8 +226,23 @@ def __add_model_geometry_to_viewer(
                     # Set material color from URDF, converting for triplet of doubles to a single int.
                     if color is None:
                         mesh_color = solid_shape.getMaterial().color()
+                    elif isinstance(color, float):
+                        mesh_color = solid_shape.getMaterial().color()
+                        mesh_color[3] = color
+                    elif isinstance(color, list):
+                        if len(color) == 4:
+                            mesh_color = color
+                        elif len(color) == 3:
+                            mesh_color = color
+                            mesh_color.append(1.0)
+                        else:
+                            mesh_color = [1.0, 1.0, 1.0, 1.0]
+                            msg = "Non compatible color type. Please pass a list if you want to specify the rgb and the alpha or just a float to specify the alpha channel."
+                            warnings.warn(msg, category=UserWarning, stacklevel=2)
                     else:
-                        mesh_color = color
+                        mesh_color = [1.0, 1.0, 1.0, 1.0]
+                        msg = "Non compatible color type. Please pass a list if you want to specify the rgb and the alpha or just a float to specify the alpha channel."
+                        warnings.warn(msg, category=UserWarning, stacklevel=2)
 
                     material.color = (
                         int(mesh_color[0] * 255) * 256 ** 2