sdfTetrahedron

fn sdfTetrahedron(position: vec3<f32>, size: f32) -> f32 {
  var p = position;
  let s = size;
  
  // Set initial values
  let signVal = sign(p.x + p.y + p.z);
  p.x = abs(p.x);
  p.y = abs(p.y);
  p.z = abs(p.z);
  
  // Calculate the distance
  if (p.x < p.y) {
    let t = p.x;
    p.x = p.y;
    p.y = t;
  }
  if (p.x < p.z) {
    let t = p.x;
    p.x = p.z;
    p.z = t;
  }
  if (p.y < p.z) {
    let t = p.y;
    p.y = p.z;
    p.z = t;
  }
  
  let k = clamp((p.x + p.z - p.y) * 0.5, 0.0, p.z);
  return signVal * (length(vec3<f32>(p.x, p.y - s, p.z - k)) - s);
}