fixed couple styles ui bugs

1) it was failing adding a new IfcSurfaceStyle if surface_style_class != Shading/Render as surface_style was not defined

2) It was never creating render material as IfcSurfaceStyleRendering class is a child of IfcSurfaceStyleShading and if statement never got to the is_a("IfcSurfaceStyleRendering") check

src/blenderbim/blenderbim/bim/module/style/operator.py

@@ -501,6 +501,9 @@ class AddPresentationStyle(bpy.types.Operator, tool.Ifc.Operator):
         props = bpy.context.scene.BIMStylesProperties
         if props.style_type == "IfcSurfaceStyle":
             style = ifcopenshell.api.run("style.add_style", tool.Ifc.get(), name=props.style_name)
+
+            # setup surface style element
+            surface_style = None
             if props.surface_style_class in ("IfcSurfaceStyleShading", "IfcSurfaceStyleRendering"):
                 surface_style = ifcopenshell.api.run(
                     "style.add_surface_style",
@@ -518,13 +521,17 @@ class AddPresentationStyle(bpy.types.Operator, tool.Ifc.Operator):
                 )
                 if props.surface_style_class == "IfcSurfaceStyleRendering":
                     surface_style.ReflectanceMethod = "NOTDEFINED"
+
+            # setup blender material
             material = bpy.data.materials.new(style.Name)
             tool.Ifc.link(style, material)
             material.use_fake_user = True
-            if surface_style.is_a("IfcSurfaceStyleShading"):
+            if surface_style:
-                tool.Loader.create_surface_style_shading(material, surface_style)
+                if surface_style.is_a("IfcSurfaceStyleRendering"):
-            elif surface_style.is_a("IfcSurfaceStyleRendering"):
+                    tool.Loader.create_surface_style_rendering(material, surface_style)
-                tool.Loader.create_surface_style_rendering(material, surface_style)
+                elif surface_style.is_a("IfcSurfaceStyleShading"):
+                    tool.Loader.create_surface_style_shading(material, surface_style)
+
         props.is_adding = False
         core.load_styles(tool.Style, style_type=props.style_type)
 

src/blenderbim/blenderbim/bim/module/style/ui.py

@@ -65,6 +65,8 @@ class BIM_PT_styles(Panel):
             row.prop(self.props, "style_name", text="Name")
             if self.props.style_type == "IfcSurfaceStyle":
                 row = box.row()
+                # NOTE: user must choose 1 of the style elements to create IfcSurfaceStyle
+                # otherwise it won't be a valid IFC
                 row.prop(self.props, "surface_style_class", text="Class")
                 if self.props.surface_style_class in ("IfcSurfaceStyleShading", "IfcSurfaceStyleRendering"):
                     row = box.row()