diff --git a/cura/LayerDataBuilder.py b/cura/LayerDataBuilder.py
index dcc3991833..1de2302f77 100644
--- a/cura/LayerDataBuilder.py
+++ b/cura/LayerDataBuilder.py
@@ -48,8 +48,10 @@ class LayerDataBuilder(MeshBuilder):
 
         self._layers[layer].setThickness(thickness)
 
-    #   material color map: [r, g, b, a] for each extruder row.
-    #   line_type_brightness: compatibility layer view uses line type brightness of 0.5
+    ##  Return the layer data as LayerData.
+    #
+    #   \param material_color_map: [r, g, b, a] for each extruder row.
+    #   \param line_type_brightness: compatibility layer view uses line type brightness of 0.5
     def build(self, material_color_map, line_type_brightness = 1.0):
         vertex_count = 0
         index_count = 0
@@ -75,9 +77,12 @@ class LayerDataBuilder(MeshBuilder):
         self.addColors(colors)
         self.addIndices(indices.flatten())
 
+        # Note: we're using numpy indexing here.
+        # See also: https://docs.scipy.org/doc/numpy/reference/arrays.indexing.html
         material_colors = numpy.zeros((line_dimensions.shape[0], 4), dtype=numpy.float32)
         for extruder_nr in range(material_color_map.shape[0]):
             material_colors[extruders == extruder_nr] = material_color_map[extruder_nr]
+        # Set material_colors with indices where line_types (also numpy array) == MoveCombingType
         material_colors[line_types == LayerPolygon.MoveCombingType] = colors[line_types == LayerPolygon.MoveCombingType]
         material_colors[line_types == LayerPolygon.MoveRetractionType] = colors[line_types == LayerPolygon.MoveRetractionType]
 
diff --git a/cura/LayerPolygon.py b/cura/LayerPolygon.py
index 90bc123548..577de9e40b 100644
--- a/cura/LayerPolygon.py
+++ b/cura/LayerPolygon.py
@@ -19,10 +19,13 @@ class LayerPolygon:
     
     __jump_map = numpy.logical_or(numpy.logical_or(numpy.arange(11) == NoneType, numpy.arange(11) == MoveCombingType), numpy.arange(11) == MoveRetractionType)
     
-    ##  LayerPolygon
-    #   line_thicknesses: array with type as index and thickness as value
-    def __init__(self, mesh, extruder, line_types, data, line_widths, line_thicknesses):
-        self._mesh = mesh
+    ##  LayerPolygon, used in ProcessSlicedLayersJob
+    #   \param extruder
+    #   \param line_types array with line_types
+    #   \param data new_points
+    #   \param line_widths array with line widths
+    #   \param line_thicknesses: array with type as index and thickness as value
+    def __init__(self, extruder, line_types, data, line_widths, line_thicknesses):
         self._extruder = extruder
         self._types = line_types
         self._data = data
diff --git a/plugins/CuraEngineBackend/ProcessSlicedLayersJob.py b/plugins/CuraEngineBackend/ProcessSlicedLayersJob.py
index 7648307de5..0f46cc96bf 100644
--- a/plugins/CuraEngineBackend/ProcessSlicedLayersJob.py
+++ b/plugins/CuraEngineBackend/ProcessSlicedLayersJob.py
@@ -139,7 +139,7 @@ class ProcessSlicedLayersJob(Job):
                     new_points[:, 1] = points[:, 2]
                     new_points[:, 2] = -points[:, 1]
 
-                this_poly = LayerPolygon.LayerPolygon(layer_data, extruder, line_types, new_points, line_widths, line_thicknesses)
+                this_poly = LayerPolygon.LayerPolygon(extruder, line_types, new_points, line_widths, line_thicknesses)
                 this_poly.buildCache()
 
                 this_layer.polygons.append(this_poly)