// Setup the Java references.
ovrJava java;
java.Vm = javaVm;
java.Env = jniEnv;
java.ActivityObject = activityObject;

// Initialize the API.
const ovrInitParms initParms = vrapi_DefaultInitParms( &java );
if ( vrapi_Initialize( &initParms ) != VRAPI_INITIALIZE_SUCCESS )
{
    FAIL( "Failed to initialize VrApi!" );
    abort();
}

// Create an EGLContext for the application.
EGLContext eglContext = ;   // application's context

// Get the suggested resolution to create eye texture swap chains.
const int suggestedEyeTextureWidth = vrapi_GetSystemPropertyInt( &java, VRAPI_SYS_PROP_SUGGESTED_EYE_TEXTURE_WIDTH );
const int suggestedEyeTextureHeight = vrapi_GetSystemPropertyInt( &java, VRAPI_SYS_PROP_SUGGESTED_EYE_TEXTURE_HEIGHT );

// Allocate a texture swap chain for each eye with the application's EGLContext current.
ovrTextureSwapChain * colorTextureSwapChain[VRAPI_FRAME_LAYER_EYE_MAX];
for ( int eye = 0; eye < VRAPI_FRAME_LAYER_EYE_MAX; eye++ )
{
    colorTextureSwapChain[eye] = vrapi_CreateTextureSwapChain3( VRAPI_TEXTURE_TYPE_2D, GL_RGBA8,
                                                                suggestedEyeTextureWidth,
                                                                suggestedEyeTextureHeight,
                                                                1, 3 );
}

// Android Activity/Surface life cycle loop.
while ( !exit )
{
    // Acquire ANativeWindow from Android Surface.

    ANativeWindow * nativeWindow = ;    // ANativeWindow for the Android Surface
    bool resumed = ;                    // set to true in onResume() and set to false in onPause()

    while ( resumed && nativeWindow != NULL )
    {
        // Enter VR mode once the Android Activity is in the resumed state with a valid ANativeWindow.
        ovrModeParms modeParms = vrapi_DefaultModeParms( &java );
        modeParms.Flags |= VRAPI_MODE_FLAG_NATIVE_WINDOW;
        modeParms.Display = eglDisplay;
        modeParms.WindowSurface = nativeWindow;
        modeParms.ShareContext = eglContext;
        ovrMobile * ovr = vrapi_EnterVrMode( &modeParms );

        // Set the tracking transform to use, by default this is eye level.
        vrapi_SetTrackingTransform( ovr, vrapi_GetTrackingTransform( ovr, VRAPI_TRACKING_TRANSFORM_SYSTEM_CENTER_EYE_LEVEL ) );

        // Frame loop, possibly running on another thread.
        for ( long long frameIndex = 1; resumed && nativeWindow != NULL; frameIndex++ )
        {
            // Get the HMD pose, predicted for the middle of the time period during which
            // the new eye images will be displayed. The number of frames predicted ahead
            // depends on the pipeline depth of the engine and the synthesis rate.
            // The better the prediction, the less black will be pulled in at the edges.
            const double predictedDisplayTime = vrapi_GetPredictedDisplayTime( ovr, frameIndex );
            const ovrTracking2 tracking = vrapi_GetPredictedTracking2( ovr, predictedDisplayTime );

            // Advance the simulation based on the predicted display time.

            // Render eye images and setup the 'ovrSubmitFrameDesc2' using 'ovrTracking2' data.

            ovrLayerProjection2 layer = vrapi_DefaultLayerProjection2();
            layer.HeadPose = tracking.HeadPose;
            for ( int eye = 0; eye < VRAPI_FRAME_LAYER_EYE_MAX; eye++ )
            {
                const int colorTextureSwapChainIndex = frameIndex % vrapi_GetTextureSwapChainLength( colorTextureSwapChain[eye] );
                const unsigned int textureId = vrapi_GetTextureSwapChainHandle( colorTextureSwapChain[eye], colorTextureSwapChainIndex );

                // Render to 'textureId' using the 'ProjectionMatrix' from 'ovrTracking2'.

                layer.Textures[eye].ColorSwapChain = colorTextureSwapChain[eye];
                layer.Textures[eye].SwapChainIndex = colorTextureSwapChainIndex;
                layer.Textures[eye].TexCoordsFromTanAngles = ovrMatrix4f_TanAngleMatrixFromProjection( &tracking.Eye[eye].ProjectionMatrix );
            }

            const ovrLayerHeader2 * layers[] =
            {
                &layer.Header
            };

            ovrSubmitFrameDescription2 frameDesc = { 0 };
            frameDesc.FrameIndex = frameIndex;
            frameDesc.DisplayTime = predictedDisplayTime;
            frameDesc.LayerCount = 1;
            frameDesc.Layers = layers;

            // Hand over the eye images to the time warp.
            vrapi_SubmitFrame2( ovr, &frameDesc );
        }
    }

    // Must leave VR mode when the Android Activity is paused or the Android Surface is destroyed or changed.
    vrapi_LeaveVrMode( ovr );
}

// Destroy the texture swap chains.
// Make sure to delete the swapchains before the application's EGLContext is destroyed.
for ( int eye = 0; eye < VRAPI_FRAME_LAYER_EYE_MAX; eye++ )
{
    vrapi_DestroyTextureSwapChain( colorTextureSwapChain[eye] );
}

// Shut down the API.
vrapi_Shutdown();