# Compute the normal of `face` and append it as 3 floats to `seq`
	#
	# Resulting normals are not normalized.
	fun compute_and_append_normal(seq: Sequence[Float], face: ObjFace)
	do
		var i1 = face.vertices[0].vertex_point_index
		var i2 = face.vertices[1].vertex_point_index
		var i3 = face.vertices[2].vertex_point_index

		var v1 = obj_def.vertex_points[i1-1]
		var v2 = obj_def.vertex_points[i2-1]
		var v3 = obj_def.vertex_points[i3-1]

		var vx = v2.x - v1.x
		var vy = v2.y - v1.y
		var vz = v2.z - v1.z
		var wx = v3.x - v1.x
		var wy = v3.y - v1.y
		var wz = v3.z - v1.z

		var nx = (vy*wz) - (vz*wy)
		var ny = (vz*wx) - (vx*wz)
		var nz = (vx*wy) - (vy*wx)

		# Append to `seq`
		seq.add nx
		seq.add ny
		seq.add nz
	end