VertexNormals

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`VertexNormals`

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is an option for graphics primitives which specifies the normal directions to assign to 3D vertices.

Details

VertexNormals can be used with Polygon, Line, Point, and GraphicsComplex.
VertexNormals->{n₁,n₂,…} specifies that vertex i should have effective normal n_i for purposes of shading by simulated lighting.
The n_i are vectors of the form {v_x,v_y,v_z}. Only the directions of these vectors ever matter; the vectors are in effect automatically normalized to unit length.
VertexNormals->None specifies that no explicit vertex normals are being given, and normal directions should be deduced from the actual coordinates specified for vertices. For point and line-like primitives, no shading based on simulated lighting should be done.
VertexNormals->Automatic is equivalent to VertexNormals->None, except that vertex normals given in any enclosing GraphicsComplex will be used.

Examples

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Basic Examples (1)Summary of the most common use cases

A triangle with all normals pointing in the direction :

In[1]:=1

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https://wolfram.com/xid/0pu89ij2cj-cvwg32

Out[1]=1

Using a different normal for one of the triangle's vertices changes the effects of lighting:

In[2]:=2

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https://wolfram.com/xid/0pu89ij2cj-dxgk6r

Out[2]=2

Specify vertex normals for 3D lines:

In[3]:=3

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https://wolfram.com/xid/0pu89ij2cj-gff7zx

Out[3]=3

Specify vertex normals for 3D points:

In[4]:=4

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https://wolfram.com/xid/0pu89ij2cj-ie9mji

Out[4]=4

Scope (2)Survey of the scope of standard use cases

Define vertices and face indices of a cylindrical model:

In[1]:=1

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https://wolfram.com/xid/0pu89ij2cj-m6rzfb

In[2]:=2

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https://wolfram.com/xid/0pu89ij2cj-fg4xff

Without surface normals, the shading is constant or flat for each polygon face:

In[3]:=3

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https://wolfram.com/xid/0pu89ij2cj-nmhii

Out[3]=3

With surface normals, the shading is interpolated or smooth across each polygon face:

In[4]:=4

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https://wolfram.com/xid/0pu89ij2cj-fovzwk

Out[4]=4

Plot functions automatically generate surface normals:

In[1]:=1

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https://wolfram.com/xid/0pu89ij2cj-dzjgj7

Out[1]=1

Without surface normals, you get flat or faceted shading:

In[2]:=2

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https://wolfram.com/xid/0pu89ij2cj-g4gxq4

Out[2]=2

Applications (3)Sample problems that can be solved with this function

A function that visualizes the surface normals using lines:

In[1]:=1

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https://wolfram.com/xid/0pu89ij2cj-6hg7b

Visualize the normals for some surfaces:

In[2]:=2

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https://wolfram.com/xid/0pu89ij2cj-cqvo3z

Out[2]=2

In[3]:=3

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https://wolfram.com/xid/0pu89ij2cj-e7s71c

Out[3]=3

Vary the effective normals used on the surface:

In[1]:=1

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https://wolfram.com/xid/0pu89ij2cj-bf0msq

Out[1]=1

A shaded mesh line object with data from ExampleData:

In[1]:=1

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https://wolfram.com/xid/0pu89ij2cj-eay1rk

Out[1]=1

Possible Issues (1)Common pitfalls and unexpected behavior

Normals in opposite directions may cause unwanted banding effects in some 3D renderers:

In[1]:=1

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https://wolfram.com/xid/0pu89ij2cj-e5jjqz

Out[1]=1

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