float sdf_circle(in vec3 p, in float radius) {
  return length(p) - radius;
}

float sdf_plane(in vec3 p, in vec3 normal, in float offset) {
  return dot(p, normal) + offset;
}

float sdf_box(in vec3 p, in vec3 dimens, in float rounding) {
  vec3 q = abs(p) - dimens + rounding;
  return length(max(q, 0.0)) + min(max(q.x, max(q.y, q.z)), 0.0) - rounding;
}

float sd_ellipsoid(vec3 p, vec3 r) {
  float k0 = length(p / r);
  float k1 = length(p / (r * r));
  return k0 * (k0 - 1.0) / k1;
}