.. _5 The Use of Pico OpenXR Play Boundary:

5 The Use of Pico OpenXR Play Boundary
========================================================

The use of the play boundary requires to set a synchronous semaphore **gsIndex** by extension, so that the HMD sensor can correspond to the camera sensor.
 
For this part, Pico provides an extension ``XR_PICO_view_state_ext_enable`` that needs to be turned on when ``xrCreateInstance`` is called. 

By passing the declared instance address of the ``XrViewStatePICOEXT`` to the next pointer of viewState and calling ``xrLocateViews`` , the synchronous semaphore **gsIndex** will be returned. 

Then, at ``xrEndFrame`` , it will be passed in by extension. The sample code is as follows. Please refer to the HelloXR Sample for details.

Getting **gsIndex** :

.. code-block:: java

 int mGsIndex;
 XrViewStatePICOEXT xrViewStatePICOEXT;
 XrViewState viewState{XR_TYPE_VIEW_STATE};
 viewState.next = (void*)&xrViewStatePICOEXT;
 xrLocateViews(mSession, &viewLocateInfo, &viewState, viewCapacityInput, &viewCountOutput, mViews.data());
 mGsIndex = xrViewStatePICOEXT.gsIndex;

Passing in **gsIndex** :

.. code-block:: java

 XrFrameEndInfoEXT xrFrameEndInfoEXT;
 xrFrameEndInfoEXT.useHeadposeExt = 1;
 xrFrameEndInfoEXT.gsIndex = mGsIndex ;
 frameEndInfo.next = (void*)&xrFrameEndInfoEXT;
 xrEndFrame(mSession, &frameEndInfo);
 
Synchronization can be achieved with the above code, and the play boundary can be used normally.

**Note:** At present, when using the play boundary, it is necessary to ensure that the ``layer`` is submitted all the time.