How fill a loaded STL mesh ( NOT SIMPLE SHAPES LIKE CUBE ETC) with random particles and animate with this geometry bound in three.js

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Okay, here it is. Works like I said: counts the number of intersected faces, and if it’s odd, then a point is inside of a mesh (geometry):

  function fillWithPoints(geometry, count) {
    
    var ray = new THREE.Ray()
    
    var size = new THREE.Vector3();
    geometry.computeBoundingBox();
    let bbox = geometry.boundingBox;
    
    let points = [];
    
    var dir = new THREE.Vector3(1, 1, 1).normalize();
    for (let i = 0; i < count; i++) {
      let p = setRandomVector(bbox.min, bbox.max);
      points.push(p);
    }
    
    function setRandomVector(min, max){
      let v = new THREE.Vector3(
        THREE.Math.randFloat(min.x, max.x),
        THREE.Math.randFloat(min.y, max.y),
        THREE.Math.randFloat(min.z, max.z)
      );
      if (!isInside(v)){return setRandomVector(min, max);}
      return v;
    }
    
    function isInside(v){
      
      ray.set(v, dir);
      let counter = 0;
      
      let pos = geometry.attributes.position;
      let faces = pos.count / 3;
      let vA = new THREE.Vector3(), vB = new THREE.Vector3(), vC = new THREE.Vector3();

      for(let i = 0; i < faces; i++){
        vA.fromBufferAttribute(pos, i * 3 + 0);
        vB.fromBufferAttribute(pos, i * 3 + 1);
        vC.fromBufferAttribute(pos, i * 3 + 2);
        if (ray.intersectTriangle(vA, vB, vC)) counter++;
      }
      
      return counter % 2 == 1;
    }
    
    return new THREE.BufferGeometry().setFromPoints(points);
  }
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