.. _4 Pico OpenXR Development:

4 Pico OpenXR Development
===============================

4.1	Overview
---------------------------------
In addition to the documentation from the Khronos Group, this section contains information needed to develop OpenXR applications for Pico devices. When setting up an OpenXR project, add the following meta-data to AndroidManifest.xml:

.. code-block:: java

 <meta-data android:name="pvr.app.type" android:value="vr" />


As OpenXR 1.0 did not include a standard Android loader, Pico has provided a custom Android loader. The loader library can be found in   **/OpenXR/Libs/Android/** in this SDK package.

On Android, the loader must be initialized with platform-specific parameters before it can be loaded. These parameters can be specified with the KHR extension  ``XR_KHR_loader_init_android``.

The KHR extension  ``XR_KHR_Loader_Init_Android`` is currently defined in **/OpenXR/Include/openxr_platform.h**. Applications are required to first get the function pointer for ``xrInitializeLoaderKHR`` via ``xrGetInstanceProcAddress`` with a null instance pointer, and then call ``xrInitializeLoaderKHR`` with the ``XrLoaderInitInfoAndroidKHR`` struct defined in ``XR_KHR_loader_init_android``.

For how the runtime is loaded, the application is required to specify its JVM and Activity. This information is provided at ``xrCreateInstance`` time via  ``XR_KHR_android_create_instance``. However, OpenXR allows specific entry points to be called before ``xrCreateInstance``. In these cases, the application will be required to call ``xrInitializeLoaderKHR`` first to provide valid JVM and Activity of the application.

4.2	Getting Started
---------------------------------

This section will guide you to get started with hello_xr, a simple cross-platform OpenXR sample in the Khronos Group’s OpenXR-SDK-Source Github repository located at **/OpenXR/Sample/HelloXR**.

The following modifications must be made to the sample in order to load the OpenXR runtime on Pico systems:

(1) Link to the OpenXR loader library in this package at **/OpenXR/Libs/Android**.

(2) In **/java/com/khronos/hello_xr/MainActivity.java**, load the openxr_loader library before loading the application shared library:

.. code-block:: java

 System.loadLibrary("openxr_loader");

(3) Add the following meta-data to AndroidManifest.xml:

.. code-block:: java

 <meta-data android:name="pvr.app.type" android:value="vr" />

(4) Before running hello_xr, make sure to specify the graphic plugin to use with one of the following adb commands:

.. code-block:: java

 adb shell setprop debug.xr.graphicsPlugin OpenGLES
 adb shell setprop debug.xr.graphicsPlugin Vulkan

(5) To reset the HMD sensor, you need to call Pico’s extension function ``xrResetSensorPICO``. Before doing this, you need to turn on the related extensions at ``xrCreateInstance`` as follows.

.. code-block:: java

 extensions.push_back(XR_PICO_CONFIGS_EXT_EXTENSION_NAME);
 extensions.push_back(XR_PICO_RESET_SENSOR_EXTENSION_NAME);

Next, execute the following to get the extension function.

.. code-block:: java

 xrGetInstanceProcAddr(m_instance,"xrGetConfigPICO",
 reinterpret_cast<PFN_xrVoidFunction *>(&pfnXrGetConfigPICO));
 xrGetInstanceProcAddr(m_instance,"xrResetSensorPICO",
 reinterpret_cast<PFN_xrVoidFunction *>(&pfnXrResetSensorPICO));

Then, use the extension ``pfnXrGetConfigPICO`` to get ``ENABLE_6DOF`` , and then call ``pfnXrResetSensorPICO`` to reset the HMD pose.
For detailed information, please refer to HelloXR Sample, in which you can reset the HMD pose by pressing the A button of controller.

(6) Setting **eyeLevel** and **floorLevel** requires to call Pico’s extension function ``xrSetConfigPICO``. To do this, you need to turn on the related extensions in ``XRCreateInstance`` as follows:

.. code-block:: java

 extensions.push_back(XR_PICO_CONFIGS_EXT_EXTENSION_NAME);

Next, excute the following to get the extension function:

.. code-block:: java

 xrGetInstanceProcAddr(m_instance,"xrSetConfigPICO", reinterpret_cast<PFN_xrVoidFunction *>(&pfnXrSetConfigPICO));

Then, set **eyeLevel/floorLevel** using the extension ``pfnXrSetConfigPICO`` after successfully creating an **xrSession**.

Set **eyeLevel**: 

.. code-block:: java

 pfnXrSetConfigPICO(m_session,TRACKING_ORIGIN,"0");

Set **floorLevel**:

.. code-block:: java

 pfnXrSetConfigPICO(m_session,TRACKING_ORIGIN,"1");