====== The role and usage of SubItem GroupID ======

A SubItem has GroupID setting.

{{ vci:sdk:groupid_1.png?nolink&530 |}}

NOTE: For details on VCI SubItem component, refer to [[en:vci:component:sdk:subitem| VCI VCI SubItem Component (VCISDK)]].

The GroupID is enabled in a VCI with multiple SubItems when **the value is set to other than 0**.

When a SubItem with a GroupID other than 0 is grabbed and the ownership is transferred, **SubItems with the same GroupID will also have their ownership transferred**.
The default value is GroupID=0, which disables this grouping function.

{{ :en:vci:sdk:subitem:groupid_2_en.png?direct |}}


===== What is this for? =====
The GroupID is used when a VCI has multiple SubItems and you want them to physically interact with each other.

{{ :en:vci:sdk:subitem:groupid_3_en.png?direct |}}

As shown on the figure above, in the world of user B, **the physics is just copied from the calculation result on the world of user A**, therefore the ball does not move.\\
The stick that moved in the world of user A will cause the ball to move and the result of that calculation is copied to the world of user B, which causes a delay.

{{ :en:vci:sdk:subitem:groupid_4_en.png?direct |}}

By hitting the ball (owned by B) with the stick (owned by B), as shown in the figure above, the physics behave correctly.\\
To recap, **GroupID is used for transferring ownership of SubItems that are grouped with a SubItem that is grabbed by a user**.

===== Use cases =====
  * Billiard. When you grab a cue, the ownership of balls also moves to you.
  * Objects connected with Joints. When you grab a part of it, the ownership of all SubItems will be transferred to you