export function calcRotationMatrix(vec, rad) {
  // Equation used from:
  // https://people.eecs.berkeley.edu/~ug/slide/pipeline/assignments/as5/rotation.html
  let A = glMatrix.mat3.fromValues(
    0,
    -vec[2],
    vec[1],
    vec[2],
    0,
    -vec[0],
    -vec[1],
    vec[0],
    0,
  );

  let I = glMatrix.mat3.create();

  // Matrix Exponential
  let Mpow = glMatrix.mat3.create();
  glMatrix.mat3.mul(Mpow, A, A);

  let M1 = glMatrix.mat3.create();
  let M2 = glMatrix.mat3.create();

  // Scalar Multiplications
  glMatrix.mat3.multiplyScalar(M1, A, Math.sin(rad));
  glMatrix.mat3.multiplyScalar(M2, Mpow, 1 - Math.cos(rad));

  // Matrix Addition
  let M3 = glMatrix.mat3.create();
  let Q = glMatrix.mat3.create();
  glMatrix.mat3.add(M3, I, M1);
  glMatrix.mat3.add(Q, M3, M2);

  return Q;
}