UIView subclass that renders a SceneKit scene using SCNRenderer

View.m

#import <UIKit/UIKit.h>
#import <SceneKit/SceneKit.h>
#import <OpenGLES/ES2/gl.h>
#import <OpenGLES/ES2/glext.h>

@interface View : UIView

@property (strong, nonatomic) SCNScene *scene;

- (void)renderFrame;

@end

@implementation View {
    EAGLContext *context;
    GLuint framebuffer;
    GLuint colorRenderbuffer;
    GLint width;
    GLint height;

    SCNRenderer *renderer;
}

+ (Class)layerClass
{
    return [CAEAGLLayer class];
}

- (BOOL)initializeOpenGL
{
    context = [[EAGLContext alloc] initWithAPI: kEAGLRenderingAPIOpenGLES2];
    [EAGLContext setCurrentContext: context];

    CAEAGLLayer *layer = (id)self.layer;
    layer.contentsScale = [UIScreen mainScreen].scale;
    layer.opaque = YES;

    glGenFramebuffers( 1, &framebuffer );
    glBindFramebuffer( GL_FRAMEBUFFER, framebuffer );
    
    glGenRenderbuffers(1, &colorRenderbuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
    if (![context renderbufferStorage:GL_RENDERBUFFER fromDrawable: layer]) return NO;
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRenderbuffer);
    
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &width);
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &height);
    
    GLuint depthRenderbuffer;
    glGenRenderbuffers(1, &depthRenderbuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, width, height);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);
    
    return glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE;
}

- (void)prepareToRender
{
    [self initializeOpenGL];

    renderer = [SCNRenderer rendererWithContext: (__bridge void *)context options: nil];
    renderer.scene = self.scene;
}

- (void)renderFrame
{
    if (!context) {
        [self prepareToRender];
    }
    
    [EAGLContext setCurrentContext: context];

    glBindFramebuffer( GL_FRAMEBUFFER, framebuffer );
    glBindRenderbuffer( GL_RENDERBUFFER, colorRenderbuffer );

    glViewport(0, 0, width, height );
    glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);

    [renderer render];

    const GLenum discards[]  = {GL_DEPTH_ATTACHMENT};
    glDiscardFramebufferEXT(GL_FRAMEBUFFER,1,discards);

    [context presentRenderbuffer:GL_RENDERBUFFER];
}

@end