#import "ViewController.h"
    #import
    #import
    #define LIGHT_DIRECTION 0, 1, -0.5
    #define AMBIENT_LIGHT 0.5
    @interface ViewController ()
    @property (nonatomic, weak) IBOutlet UIView *containerView;
    @property (nonatomic, strong) IBOutletCollection(UIView) NSArray *faces;
    @end
    @implementation ViewController
    - (void)applyLightingToFace:(CALayer *)face
    {
        //add lighting layer
        CALayer *layer = [CALayer layer];
        layer.frame = face.bounds;
        [face addSublayer:layer];
        //convert the face transform to matrix
        //(GLKMatrix4 has the same structure as CATransform3D)
        CATransform3D transform = face.transform;
        GLKMatrix4 matrix4 = *(GLKMatrix4 *)&transform;
        GLKMatrix3 matrix3 = GLKMatrix4GetMatrix3(matrix4);
        //get face normal
        GLKVector3 normal = GLKVector3Make(0, 0, 1);
        normal = GLKMatrix3MultiplyVector3(matrix3, normal);
        normal = GLKVector3Normalize(normal);
        //get dot product with light direction
        GLKVector3 light = GLKVector3Normalize(GLKVector3Make(LIGHT_DIRECTION));
        float dotProduct = GLKVector3DotProduct(light, normal);
        //set lighting layer opacity
        CGFloat shadow = 1 + dotProduct - AMBIENT_LIGHT;
        UIColor *color = [UIColor colorWithWhite:0 alpha:shadow];
        layer.backgroundColor = color.CGColor;
    }
    - (void)addFace:(NSInteger)index withTransform:(CATransform3D)transform
    {
        //get the face view and add it to the container
        UIView *face = self.faces[index];
        [self.containerView addSubview:face];
        //center the face view within the container
        CGSize containerSize = self.containerView.bounds.size;
        face.center = CGPointMake(containerSize.width / 2.0, containerSize.height / 2.0);
        // apply the transform
        face.layer.transform = transform;
        //apply lighting
        [self applyLightingToFace:face.layer];
    }
    - (void)viewDidLoad
    {
        [super viewDidLoad];
        //set up the container sublayer transform
        CATransform3D perspective = CATransform3DIdentity;
        perspective.m34 = -1.0 / 500.0;
        perspective = CATransform3DRotate(perspective, -M_PI_4, 1, 0, 0);
        perspective = CATransform3DRotate(perspective, -M_PI_4, 0, 1, 0);
        self.containerView.layer.sublayerTransform = perspective;
        //add cube face 1
        CATransform3D transform = CATransform3DMakeTranslation(0, 0, 100);
        [self addFace:0 withTransform:transform];
        //add cube face 2
        transform = CATransform3DMakeTranslation(100, 0, 0);
        transform = CATransform3DRotate(transform, M_PI_2, 0, 1, 0);
        [self addFace:1 withTransform:transform];
        //add cube face 3
        transform = CATransform3DMakeTranslation(0, -100, 0);
        transform = CATransform3DRotate(transform, M_PI_2, 1, 0, 0);
        [self addFace:2 withTransform:transform];
        //add cube face 4
        transform = CATransform3DMakeTranslation(0, 100, 0);
        transform = CATransform3DRotate(transform, -M_PI_2, 1, 0, 0);
        [self addFace:3 withTransform:transform];
        //add cube face 5
        transform = CATransform3DMakeTranslation(-100, 0, 0);
        transform = CATransform3DRotate(transform, -M_PI_2, 0, 1, 0);
        [self addFace:4 withTransform:transform];
        //add cube face 6
        transform = CATransform3DMakeTranslation(0, 0, -100);
        transform = CATransform3DRotate(transform, M_PI, 0, 1, 0);
        [self addFace:5 withTransform:transform];
    }
    @end