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# Finding the Normal of a Face

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OK, I know that this has been answered before in these forums, but I cant seem to find an answer as to how you find the normal of a face when you have the three vertices, and the winding order(counter clockwise or clockwise) of the face. Thanks

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You create to vectors like this.

Vector1 = Vertex2 - Vertex1
Vector2 = Vertex3 - Vertex1

Then the normal of the face is just the
crossproduct between these two.

VecNormal = Dot(Vector1, Vector2)

Oh, and I think you should normalize both
Vector1 and Vector2 before you calculate
the dotproduct.

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Yeah, although I wouldn''t normalise the vectors before taking the cross product. You would normalise the face''s normal after taking the cross product, so doing two of them beforehand is unneeded calculation.

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Thanks CrazySwede and Beer Hunter.

Edited by - cooltomk on August 7, 2001 12:34:55 PM

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Also, there''s a tutorial on my page about back-face culling, which includes showing you how to calculate face normals.

http://www.sbdev.pwp.blueyonder.co.uk/tutorials/tut4.htm

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