Detect a flat surface on a complex mesh?

Question

I am trying to write a script that can detect, wether or not a given object has a flat surface somewhere on it's mesh or not.

For instance, a sphere would be a negative, where as a cube would be a positive, as this has at least one flat surface. Furthermore, a capsule would be a negative, where as a cylinder would be a positive, as the two sides of this are flat.

How do I go about doing this?

Thanks in advance.

Answer 1

Best Answer

Answer by Bunny83 · Jun 18, 2014 at 06:03 PM

Actually all surfaces are technically flat as all geometry is made up with triangles. However if you mean at least 1 flat-shaded surface, then you just have to compare the 3 vertex normals of each triangle. If they are equal, it's flatshaded. Something like this:

 // C#
 bool HasFlatshadedSurface(Mesh m)
 {
     Vector3[] normals = m.normals;
     int[] indices = m.triangles;
     int triangleCount = indices.Count / 3;
     for(int i = 0; i < triangleCount; i++)
     {
         Vector3 n1 = normals[indices[i*3    ]];
         Vector3 n2 = normals[indices[i*3 + 1]];
         Vector3 n3 = normals[indices[i*3 + 2]];
         if (n1 == n2 and n1 == n3)
             return true;
     }
     return false;
 }

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Vicas · Jun 19, 2014 at 06:08 AM 0

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That makes sense. I should probably have said that the surface also had to be horizontal, but from your code I can take it from there, the normals just have to be the same direction as some Vector.up I figure.

Navy_Seals · Oct 14, 2021 at 10:08 AM 0

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@Bunny83 Suppose if I want to know whether the area of the mesh is flat or not at which point I am raycasting with a square or rectangle boundary on it. How do I achieve this? Any suggestions?

Detect a flat surface on a complex mesh?

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