# Understanding the Treasure Hunt sample ## Code walkthrough This walkthrough shows you how the iOS sample Treasure Hunt handles the following tasks: - Implement a [`UIViewController`](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewController_Class/) to host [`GVRCardboardView`](https://developers.google.com/vr/ios/reference/interface_g_v_r_cardboard_view). - Define a renderer to implement the [`GVRCardboardViewDelegate`](https://developers.google.com/vr/ios/reference/protocol_g_v_r_cardboard_view_delegate-p) protocol. - Add a render loop using the [`CADisplayLink`](https://developer.apple.com/library/prerelease/ios/documentation/QuartzCore/Reference/CADisplayLink_ClassRef/index.html) object. - Handle inputs. ### Implement a UIViewController to host GVRCardboardView The TreasureHunt app implements a [`UIViewController`](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewController_Class/), the `TreasureHuntViewController` class. This UIViewController class has an instance of [`GVRCardboardView`](https://developers.google.com/vr/ios/reference/interface_g_v_r_cardboard_view) class. An instance of the `TreasureHuntRenderer` class is created and set as a [`GVRCardboardViewDelegate`](https://developers.google.com/vr/ios/reference/protocol_g_v_r_cardboard_view_delegate-p) for the `GVRCardboardView`. In addition, the app provides a render loop, the `TreasureHuntRenderLoop` class, that drives the [`-render`](https://developers.google.com/vr/ios/reference/interface_g_v_r_cardboard_view#method-detail) 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`](https://developers.google.com/vr/ios/reference/interface_g_v_r_cardboard_view) provides a drawing surface for your rendering. It coordinates the drawing with your rendering code through the [`GVRCardboardViewDelegate`](https://developers.google.com/vr/ios/reference/protocol_g_v_r_cardboard_view_delegate-p) protocol. To achieve this, the `TreasureHuntRenderer` class implements `GVRCardboardViewDelegate`: #import "GVRCardboardView.h" /** TreasureHunt renderer. */ @interface TreasureHuntRenderer : NSObject @end ### Implement the GVRCardboardViewDelegate protocol To draw the GL content onto [`GVRCardboardView`](https://developers.google.com/vr/ios/reference/interface_g_v_r_cardboard_view), `TreasureHuntRenderer` implements the [`GVRCardboardViewDelegate`](https://developers.google.com/vr/ios/reference/protocol_g_v_r_cardboard_view_delegate-p) protocol: @protocol GVRCardboardViewDelegate - (void)cardboardView:(GVRCardboardView *)cardboardView didFireEvent:(GVRUserEvent)event; - (void)cardboardView:(GVRCardboardView *)cardboardView willStartDrawing:(GVRHeadTransform *)headTransform; - (void)cardboardView:(GVRCardboardView *)cardboardView prepareDrawFrame:(GVRHeadTransform *)headTransform; - (void)cardboardView:(GVRCardboardView *)cardboardView drawEye:(GVREye)eye withHeadTransform:(GVRHeadTransform *)headTransform; - (void)cardboardView:(GVRCardboardView *)cardboardView shouldPauseDrawing:(BOOL)pause; @end Implementations for the `willStartDrawing`, `prepareDrawFrame`, and `drawEye` methods are described below. #### Implement willStartDrawing To perform one-time GL state initialization, implement [`-cardboardView:willStartDrawing:`](https://developers.google.com/vr/ios/reference/protocol_g_v_r_cardboard_view_delegate-p#method-detail). Use this opportunity to load shaders, initialize scene geometry, and bind to GL parameters. We also initialize an instance of the [`GVRCardboardAudioEngine`](https://developers.google.com/vr/ios/reference/interface_g_v_r_audio_engine) 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: kRenderingModeBinauralHighQuality]; [_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:`](https://developers.google.com/vr/ios/reference/protocol_g_v_r_cardboard_view_delegate-p#method-detail). 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 = GLKQuaternionMakeWithMatrix4(GLKMatrix4Transpose( [headTransform headPoseInStartSpace])); [_cardboard_audio_engine setHeadRotation:head_rotation.q[0] y:head_rotation.q[1] z:head_rotation.q[2] w:head_rotation.q[3]]; // Update the audio engine. [_cardboard_audio_engine update]; // Clear the GL viewport. glClearColor(0.0f, 0.0f, 0.0f, 1.0f); glEnable(GL_DEPTH_TEST); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glEnable(GL_SCISSOR_TEST); } #### Implement drawEye The [`drawEye`](https://developers.google.com/vr/ios/reference/protocol_g_v_r_cardboard_view_delegate-p#method-detail) 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 drawEye:(GVREye)eye withHeadTransform:(GVRHeadTransform *)headTransform { // Set the viewport. CGRect viewport = [headTransform viewportForEye:eye]; glViewport(viewport.origin.x, viewport.origin.y, viewport.size.width, viewport.size.height); glScissor(viewport.origin.x, viewport.origin.y, viewport.size.width, viewport.size.height); // 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(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`](https://developers.google.com/vr/ios/reference/interface_g_v_r_cardboard_view) renders the scene to the display. ### Add a render loop using CADisplayLink The rendering needs to be driven by a render loop using [`CADisplayLink`](https://developer.apple.com/library/prerelease/ios/documentation/QuartzCore/Reference/CADisplayLink_ClassRef/index.html). The TreasureHunt app provides a sample render loop: `TreasureHuntRenderLoop`. This needs to call the [`-render`](https://developers.google.com/vr/ios/reference/interface_g_v_r_cardboard_view#method-detail) method of the [`GVRCardboardView`](https://developers.google.com/vr/ios/reference/interface_g_v_r_cardboard_view) class. This is handled in the [`-viewWillAppear:`](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewController_Class/#//apple_ref/occ/instm/UIViewController/viewWillAppear:) and [`- viewDidDisappear:`](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewController_Class/#//apple_ref/occ/instm/UIViewController/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:`](https://developers.google.com/vr/ios/reference/protocol_g_v_r_cardboard_view_delegate-p#method-detail) 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. break; case kGVRUserEventTrigger: NSLog(@"User performed trigger action"); // Check whether the object is found. if (_is_cube_focused) { // Vibrate the device on success. AudioServicesPlaySystemSound(kSystemSoundID_Vibrate); // Generate the next cube. [self spawnCube]; } break; } }