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Creating polygon from normal

Started by Xero_Tolerance May 3, 2004 at 6:27 PM 0 replies 550+ views

Original Post

May 3, 2004 at 6:27 PM

Basically I''m trying to work on a lighting system. I have it all setup but with a few problems. Basically the problem is I have a normal from a polygon and the intersection point. How would I make a square of size X that lies on the same plane as the normal originated from and make sure the intersection point is the center of the square. Any help would be much appreciated, thanks.

JohnBolton

132

JohnBolton

May 4, 2004 at 2:55 AM

The first problem is that there are an infinite number of squares that meet your requirements. You need to somehow cut it down to one. If N is the normal, P is the intersection, L is the light direction, and P_1,2,3,4 are the corners of the square, you can do it like this as long as L != N and L != -N:

U = N cross L
Normalize U
V = N cross U
P₁ = P + ( -U + -V ) * X / 2
P₂ = P + ( -U +  V ) * X / 2
P₃ = P + (  U + -V ) * X / 2
P₄ = P + (  U +  V ) * X / 2

Actually, you can replace L with any vector as long as it is not in the same or the opposite direction of N.

John Bolton
Page 44 Studios
Current project: NHL Faceoff 2005 PS2

[edited by - JohnBolton on May 4, 2004 3:59:00 AM]

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