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konstantin magnus

Replicating circular points around normals

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Posted (edited)

I am currently using cross products and matrix transformations to replicate points in circles that are oriented by normals.


Are there any more straight forward ways to achieve this with VEX?

int points = chi('points');
float scale = 0.02;

vector up = {0, 1, 0};

for(int i = 0; i < points; i++){
    vector dir = normalize( cross(@N, up) );
    float amount = (i / float(points)) * $PI * 2;
    matrix m = ident();
    rotate(m, amount, @N);
    dir *= m;
    dir *= scale;
    int pt = addpoint(0, @P + dir);


Edited by konstantin magnus

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You can simplify it a bit using sample_circle_uniform and dihedral functions:

for(int i = 0; i < points; i++){
  float u = i / float(points);
  vector p = sample_circle_uniform(set(u, ch("r")));
  matrix m = dihedral({0,1,0}, @N);
  addpoint(0, @P + set(p.x, 0, p.y) * m);


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So you 

  • create "flat" circle coordinates based on u with sample_circle_uniform() and scale them immediately by adding a second vector component to "u" as a radius argument,
  • calculate a rotation matrix based on the difference between an up vector and the point´s normal with dihedral(), and
  • transpose the 2D circle coordinates to a vector3, multiplying it by the rotation matrix and adding that to the current point position.

Now that´s clever!

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