Normals determine whether a given triangle face is lit.

法线会判断指定的三角形表面是否会被照亮。

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During the operation, teams of doctors grafted a triangle of tissue including a nose, lips and chin onto the face of the 38-year-old divorced mother of two teenaged daughters, who had been attacked by a Labrador and whose name has not been disclosed.

CNN: Face transplant woman thanks team

His face was smeared with sandalwood, and he wore a loose-fitting silk shirt through which a dark triangle of chest hair stuck out.

NEWYORKER: The Elephant