NormalsFunction

is an option for Plot3D and related functions that specifies a function to apply to determine the effective surface normals at every point.

Details

	None	determine normals from explicit polygon vertices
	Automatic	determine normals from overall surface properties
	f	determine normals by applying a function f

With NormalsFunction->f, the arguments supplied to f are as follows:
Plot3D x, y, z

ParametricPlot3D x, y, z, u, v

ContourPlot3D x, y, z, w

RegionPlot3D x, y, z
The function f must return a vector of the form {v_x,v_y,v_z}. Only the direction of this vector matters; the vector is in effect automatically normalized to unit length.

Use automatic methods to compute surface normals:

Make the effective normals to the surface vary locally:

Use flat shading for all polygons:

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