相邻三角形Three.js的面积

Question

I am trying to find the area of triangles adjacent to a particular vertex in a mesh in Three.js.

I know that faces in three.js represent how vertices in a mesh are connected, but I haven't found an efficient way to find the set of indices of all triangles adjacent to a specific vertex.

The code below is the best I could come up with, but given a large mesh with over 16,000 vertices (non-duplicated) and over 5,000 faces, the loop is running > 80m times which takes way too long.

Also, my if function that checks whether the a, b, or c position in a face matches that of the vertex currently in the loop does not work at all.

var objectFace = object.geometry.faces;
var objectVertex = object.geometry.vertices;

    for( var m = 0; m < objectVertex.length; m++ ) {
        for( var q = 0; q < objectFace.length; q++ ) {

            fArray = objectFace[q];

            if ( fArray.a = m || fArray.b = m || fArray.c = m ) {
            var va = fArray.a;
            var vb = fArray.b;
            var vc = fArray.c;

            var v1 = objectVertex[va];
            var v2 = objectVertex[vb];
            var v3 = objectVertex[vc];

            var vec1 = [( v2.x - v1.x ), ( v2.y - v1.y ), ( v2.z - v1.z )];
            var vec2 = [( v3.x - v1.x ), ( v3.y - v1.y ), ( v3.z - v1.z )];

            //calculate area of triangle with Heron's equation
            //store area values in array

        }
    };
};

I then calculate the area by crossing the two vectors and plugging them in to Heron's equation.

Any help is greatly appreciated.

*ps I know my JS skills are not very good but this is the best I could come up with.

Answer 1

It seems that you're trying to do this for all vertices. So instead of looping trough every vertex, every face, and then sorting out the non-incident faces, you could just loop over the faces and accumulate the results for the according vertices:

[Pseudo code]
for each face
    a := calculate face area
    areas[facce.first vertex] += a
    areas[facce.second vertex] += a
    areas[facce.third vertex] += a
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