====== Synchronizing the state of items ======

The position, rotation and scale of items are automatically synchronized by SubItem.
In this page, we will explain how to synchronize other elements, such as on/off of a switch or a counter.

As an example, we will switch the on/off state of a switch with onUse (pressing on the grip button while grabbing a SubItem).
When the switch is off, change the color of the material 0 to white, when on, change the color of the material 0 to red.

----

===== Method 1: use _ALL_ functions ======

Use _ALL_ functions to run commands on all users simultaneously.

<code lua>
isRed = false -- not local
 
function onUse()
    isRed = not isRed -- flip the true, false
    if isRed then
        vci.assets._ALL_SetMaterialColorFromIndex(0, Color.__new(1, 0, 0, 1)) -- Red
    else
        vci.assets._ALL_SetMaterialColorFromIndex(0, Color.__new(1, 1, 1, 1)) -- white
    end
end</code>

It seems simple, but it doesn't work in the following situations

  * The color doesn't change on the user who joined the room in the middle of the session.
  * When another user grabbed the item and pressed the grip button (The variable holding the state of the color is in the original user; thus it won't be transferred with the ownership)

===== Method 2: Run the command on all users though Item Sync Variable =====

Use the [[en/vci/script/reference/exportstate|vci.state]].

<code lua>
if vci.assets.isMine then
    -- Initialize with the item spawn, only in the user who spawned it
    vci.state.Set('isRed', false) -- Initial value. `nil` is set if nothing is done to it
end
 
function onUse()
  local isRed = vci.state.Get('isRed') -- Acquire true or false local
  vci.state.Set('isRed', not isRed) -- Just change the state, not the actual color
end
 
function updateAll() -- Use updateAll because this needs to be run on every users.
    local isRed = vci.state.Get('isRed') -- Acquire the state. The item sync variable will be the same in all users (synced) local
    if isRed then
        vci.assets.SetMaterialColorFromIndex(0, Color.__new(1, 0, 0, 1)) -- Red
    else
        vci.assets.SetMaterialColorFromIndex(0, Color.__new(1, 1, 1, 1)) -- white
    end
end</code>

===== Which method to use =====

  * _ALL_ can be used for one-shot, one-way usages like playing a short sound.
  * The item sync variable can be used for everything else