code: function capsuleVsCapsule(contactPoint, contactNormal, capsuleA, capsuleB) {
    findClosestPointsFromSegmentToSegment(tmpVec1, tmpVec2,
        capsuleA.segment, capsuleB.segment);
    vec3.subtract(contactNormal, tmpVec2, tmpVec1);
    vec3.normalize(contactNormal, contactNormal);
    vec3.scaleAndAdd(contactPoint, tmpVec1, contactNormal, capsuleA.radius);
  }
docs: Finds the closest point on the surface of capsule A to capsule B.
  
  @param {vec3} contactPoint Output param.
  @param {vec3} contactNormal Output param.
  @param {Capsule} capsuleA
  @param {Capsule} capsuleB