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Hello,

How can I calculate the normal vector giving a vertex on a 2D plane in OpenGL. ?

All what I read was all about 3D and cross product of two vectors. the only thing that I have is that vertex and I want to construct a vector coming out of it.

any help?

Thanks

Edited by jowana: n/a

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Last Post by jowana
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The problem isn't with OpenGL - it is just an interface to display stuff on the screen. Calculating the vector is the main problem. That is simple calculus or vector algebra. Refresh your math and go from there!

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the reason for drawing this vector is to be the start of my rotation,
thats why I chose openGL becuase i need to apply some graphics after that.

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giving a vertex on a 2D plane

What information do you have about the plane? (equations, points, etc?)

This does a nice job of explaining things.

Edited by jonsca: n/a

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To get the normal out of a vertex on the edge of a 2D polygon, you take the vector that goes from the point just before to the point just after, and then you rotate that vector by 90 degrees ccw (right-hand rule). You can do that by swaping (x,y) with (-y,x). That's all! (it's actually the same as taking the cross-product, in 3D, with a vector pointing directly out of the 2D plane).

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