Understanding the Treasure Hunt sample

Code walkthrough

This walkthrough shows you how the iOS sample Treasure Hunt handles the following tasks:

Implement a UIViewController to host GVRCardboardView

The TreasureHunt app implements a UIViewController, the TreasureHuntViewController class. This UIViewController class has an instance of GVRCardboardView class. An instance of the TreasureHuntRenderer class is created and set as a GVRCardboardViewDelegate for the GVRCardboardView. In addition, the app provides a render loop, the TreasureHuntRenderLoop class, that drives the -render method of the GVRCardboardView.

- (void)loadView {
  _treasureHuntRenderer = [[TreasureHuntRenderer alloc] init];
  _treasureHuntRenderer.delegate = self;

  _cardboardView = [[GVRCardboardView alloc] initWithFrame:CGRectZero];
  _cardboardView.delegate = _treasureHuntRenderer;
  _cardboardView.vrModeEnabled = YES;
  self.view = _cardboardView;

Define a renderer to implement the GVRCardboardViewDelegate protocol

GVRCardboardView provides a drawing surface for your rendering. It coordinates the drawing with your rendering code through the GVRCardboardViewDelegate protocol. To achieve this, the TreasureHuntRenderer class implements GVRCardboardViewDelegate:

#import "GVRCardboardView.h"

/** TreasureHunt renderer. */
@interface TreasureHuntRenderer : NSObject<GVRCardboardViewDelegate>


Implement the GVRCardboardViewDelegate protocol

To draw the GL content onto GVRCardboardView, TreasureHuntRenderer implements the GVRCardboardViewDelegate protocol:

@protocol GVRCardboardViewDelegate<NSObject>

- (void)cardboardView:(GVRCardboardView *)cardboardView

- (void)cardboardView:(GVRCardboardView *)cardboardView
     willStartDrawing:(GVRHeadTransform *)headTransform;

- (void)cardboardView:(GVRCardboardView *)cardboardView
     prepareDrawFrame:(GVRHeadTransform *)headTransform;

- (void)cardboardView:(GVRCardboardView *)cardboardView
    withHeadTransform:(GVRHeadTransform *)headTransform;

- (void)cardboardView:(GVRCardboardView *)cardboardView


Implementations for the willStartDrawing, prepareDrawFrame, and drawEye methods are described below.

Implement willStartDrawing

To perform one-time GL state initialization, implement -cardboardView:willStartDrawing:. Use this opportunity to load shaders, initialize scene geometry, and bind to GL parameters. We also initialize an instance of the GVRCardboardAudioEngine class here:

- (void)cardboardView:(GVRCardboardView *)cardboardView
     willStartDrawing:(GVRHeadTransform *)headTransform {
  // Load shaders and bind GL attributes.
  // Load mesh and model geometry.
  // Initialize GVRCardboardAudio engine.
  _cardboard_audio_engine =
  [[GVRCardboardAudioEngine alloc]initWithRenderingMode:
  [_cardboard_audio_engine preloadSoundFile:kSampleFilename];
  [_cardboard_audio_engine start];
  [self spawnCube];

Implement prepareDrawFrame

To set up rendering logic before the individual eyes are rendered, implement -cardboardView:prepareDrawFrame:. Any per-frame operations specific to this rendering should happen here. This is a good place to update your model and clear the GL state for drawing. The app computes the head orientation and updates the audio engine.

- (void)cardboardView:(GVRCardboardView *)cardboardView
     prepareDrawFrame:(GVRHeadTransform *)headTransform {
  GLKMatrix4 head_from_start_matrix = [headTransform headPoseInStartSpace];
  // Update audio listener's head rotation.
  const GLKQuaternion head_rotation =
      [headTransform headPoseInStartSpace]));
  [_cardboard_audio_engine setHeadRotation:head_rotation.q[0]
  // Update the audio engine.
  [_cardboard_audio_engine update];

  // Clear the GL viewport.
  glClearColor(0.0f, 0.0f, 0.0f, 1.0f);

Implement drawEye

The drawEye delegate provides the core of the rendering code, similar to building a regular OpenGL ES application.

The following snippet shows how to implement drawEye to get the view transformation matrix for each eye and the perspective transformation matrix. Note that this method gets called for each eye. If the GVRCardboardView does not have VR mode enabled, then eye is set to the center eye. This is useful for monoscopic rendering, to provide a non-VR view of the 3D scene.

- (void)cardboardView:(GVRCardboardView *)cardboardView
    withHeadTransform:(GVRHeadTransform *)headTransform {
  // Set the viewport.
  CGRect viewport = [headTransform viewportForEye:eye];
  glViewport(viewport.origin.x, viewport.origin.y, viewport.size.width,
  glScissor(viewport.origin.x, viewport.origin.y, viewport.size.width,

  // Get the head matrix.
  const GLKMatrix4 head_from_start_matrix =
      [headTransform headPoseInStartSpace];

  // Get this eye's matrices.
  GLKMatrix4 projection_matrix = [headTransform
      projectionMatrixForEye:eye near:0.1f far:100.0f];
  GLKMatrix4 eye_from_head_matrix =
      [headTransform eyeFromHeadMatrix:eye];

  // Compute the model view projection matrix.
  GLKMatrix4 model_view_projection_matrix =
      GLKMatrix4Multiply(eye_from_head_matrix, head_from_start_matrix));

  // Render from this eye.
  [self renderWithModelViewProjectionMatrix:model_view_projection_matrix.m];

After returning from this call, GVRCardboardView renders the scene to the display.

The rendering needs to be driven by a render loop using CADisplayLink. The TreasureHunt app provides a sample render loop: TreasureHuntRenderLoop. This needs to call the -render method of the GVRCardboardView class. This is handled in the -viewWillAppear: and - viewDidDisappear: methods of the TreasureHuntViewController class:

- (void)viewWillAppear:(BOOL)animated {
  [super viewWillAppear:animated];

  _renderLoop = [[TreasureHuntRenderLoop alloc]
   initWithRenderTarget:_cardboardView selector:@selector(render)];

- (void)viewDidDisappear:(BOOL)animated {
  [super viewDidDisappear:animated];

  [_renderLoop invalidate];
  _renderLoop = nil;

Handling inputs

The Google VR SDK detects events fired when the user presses the viewer button.

To provide custom behavior when these events occur, implement the -cardboardView:didFireEvent: delegate method.

- (void)cardboardView:(GVRCardboardView *)cardboardView
         didFireEvent:(GVRUserEvent)event {
  switch (event) {
    case kGVRUserEventBackButton:
    // If the view controller is in a navigation stack or
    // over another view controller, pop or dismiss the
    // view controller here.
    case kGVRUserEventTrigger:
     NSLog(@"User performed trigger action");
     // Check whether the object is found.
     if (_is_cube_focused) {
       // Vibrate the device on success.
       // Generate the next cube.
       [self spawnCube];