# Compute the normals of `faces` in a flat `Array[Float]`
	fun normals(faces: Array[ObjFace]): Array[Float] do
		var obj_def = obj_def

		var normals = new Array[Float]
		for face in faces do
			# 1st triangle
			var count = 0
			for e in face.vertices do
				var i = e.normal_index
				if i == null then
					compute_and_append_normal(normals, face)
				else
					var v = obj_def.normals[i-1]
					normals.add v.x
					normals.add v.y
					normals.add v.z
				end

				if count == 2 then break
				count += 1
			end

			# If square, 2nd triangle
			#
			# This may not support all vertices ordering.
			if face.vertices.length > 3 then
				for e in [face.vertices[0], face.vertices[2], face.vertices[3]] do
					var i = e.normal_index
					if i == null then
						compute_and_append_normal(normals, face)
					else
						var v = obj_def.normals[i-1]
						normals.add v.x
						normals.add v.y
						normals.add v.z
					end
				end
			end
		end
		return normals
	end