normal
abstract MutableQuadView normal(int vertexIndex, float x, float y, float z)
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Adds a vertex normal. Models that have per-vertexnormals should include them to get correct lighting when it matters.Computed face normal is used when no vertex normal is provided.
Renderer implementations should honor vertex normals fordiffuse lighting - modifying vertex color(s) or packing normals in the vertexbuffer as appropriate for the rendering method/vertex format in effect.
Same as normal but accepts vector type.