.. _bpy.types.NormalEditModifier:

********************
Normal Edit Modifier
********************

The *Normal Edit* modifier affects (or generates) custom normals. It uses a few simple parametric methods
to compute them (quite useful in game development and architecture areas), and mixes back those generated normals
with existing ones.


Options
=======

.. figure:: /images/modeling_modifiers_modify_normal-edit_panel.png
   :align: right

   Normal Edit Modifier.

Mode
   Radial
      Aligns normals with the ``(origin, vertex_coordinates)`` vector, in other words all normals seems to radiate
      from the given center point, as if they were emitted from an ellipsoid surface.
   Directional
      Makes all normals point (converge) towards a given target object.

Target Object
   Uses this object's origin as reference point when generating normals.

   Optional in *Radial* mode, mandatory in *Directional* one.

Parallel Normals
   Makes all normals parallel to the line between both objects' origins,
   instead of converging towards target's origin.

   Only relevant in *Directional* mode.

Offset
   Gives modified object's origin an offset before using it to generate normals.

   Only relevant in *Radial* mode if no *Target Object* is set,
   and in *Directional* mode when *Parallel Normals* is set.


Mix Mode
--------

Mix Mode
   How to affect existing normals with newly generated ones.

   Note that the *Multiply* option is **not** a cross product, but a mere component-by-component multiplication.
Mix Factor
   How much of the generated normals get mixed into existing ones.
Vertex Group
   Allows per-item fine control of the mix factor. The vertex group influence can be reverted by using the small
   "arrow" button to the right.
Max Angle
   Forbids new generated normals to have an angle to the original normal above that given threshold.
   This is useful to prevent extreme changes, that can even lead to inverting the front/back sides of a face,
   and consequently to ugly shading artifacts.
Lock Polygon Normals (padlock icon)
   Prevents flipping (reversing front/back sides) of polygons which normal does not match anymore
   the side to which point its corners' custom normals. Can also help avoiding shading issues.


Usage
=====

This modifier can be used to quickly generate radial normals for low-poly tree foliage or
"fix" shading of toon-like rendering by partially bending default normals...

The only mandatory prerequisite to use it is to enable the *Auto Smooth* option in Mesh properties, *Normals* panel.

.. tip::

   More complex normal manipulations can be achieved by copying normals from one mesh to another,
   see the :doc:`Data Transfer Modifier </modeling/modifiers/modify/data_transfer>`.
   Some shading effects can also make use of
   the :doc:`Weighted Normals modifier </modeling/modifiers/modify/weighted_normal>`.


Example
=======

.. figure:: /images/modeling_modifiers_modify_normal-edit_example.jpg
   :width: 680px

   Examples of editing custom normals to point towards a given direction,
   see `example blend-file <http://download.blender.org/ftp/mont29/persistent_data/sapling_CN.blend>`__.

The left tree mesh has unmodified normals, while on the right one a *Normal Edit* modifier is used to bend them
towards the camera. This shading trick is often used in games to fake scattering in trees and other vegetation.