U3D差集判断是否在左边或右边

默认用法，不支持旋转：

var cross = Vector3.Cross(lhsObject.transform.position, rhsObject.transform.position);
if (cross.y > 0) //side
if(cross.y < 0)//another side

用forward,从而支持旋转：

void OnCollisionEnter(Collision other) {
     Vector3 direction = other.contacts[0].point - transform.position;
     var cross = Vector3.Cross(transform.forward, direction);
     if (cross.y < 0) print ("Left");
         else print("right");
 }

 function OnCollisionEnter(other:Collision){
     var direction:Vector3 = other.contacts[0].point - transform.position;
     var cross :Vector3 = Vector3.Cross(transform.forward, direction);
     if (cross.y < 0) print ("Left");
         else print("right");
 }

论坛上还看见一个demo，加深对差集的理解：(得到一个forward方向，取得up,right,left)

// original vector:
  var forward: Vector3 = Vector3(0.5, 0.7, 0.8);
  // up direction:
  var up: Vector3 = Vector3(0.0, 1.0, 0.0);
  // find right vector:
  var right = Vector3.Cross(forward.normalized, up.normalized);
  var left = -right;