polygon/triangle in clockwise order

Recommended Posts

Hello all. Do anyone know a good way to sort and check if a polygon/triangle is in a clockwise order? /Luger

Share on other sites
Depends on what you mean. There's no such thing as a polygon that is inheritly "clockwise" in order. It depends on the angle from which you view it at. That's how backface culling works in most graphics API's.

Share on other sites
I know, just had a small error in my code, and everything works now.... =)

Share on other sites
First, note that a triangle ABC can only be classified as clockwise or counterclockwise as viewed from a given position P not in the plane of the triangle.

So, given ABC and P, you can do this:

Vector normal = Cross(B - A, C - A);bool counterclockwise = Dot(normal, P - A) > 0;

What P is depends on your application. It might be the camera position, the world origin, a vertex of some other triangle, or something else entirely.

If your triangle is not in 3D but in 2D, you can simplify the test accordingly (knowing that z = 0).

Create an account

Register a new account

• Forum Statistics

• Total Topics
627741
• Total Posts
2978887

• 10
• 10
• 21
• 14
• 14