main_view.m

@interface MainView : NSView
@end

@implementation MainView
{
	id<MTLDevice> device;
	id<MTLCommandQueue> commandQueue;
	CADisplayLink *displayLink;
	id<MTLRenderPipelineState> pipelineState;

	IOSurfaceRef framebufferSurface;
	id<MTLTexture> framebuffer;
}

- (instancetype)initWithFrame:(NSRect)frame
{
	self = [super initWithFrame:frame];
	self.wantsLayer = YES;

	device = MTLCreateSystemDefaultDevice();
	commandQueue = [device newCommandQueue];

	NSBundle *bundle = [NSBundle mainBundle];
	NSURL *libraryURL = [bundle URLForResource:@"shaders" withExtension:@"metallib"];
	id<MTLLibrary> library = [device newLibraryWithURL:libraryURL error:nil];

	MTLRenderPipelineDescriptor *descriptor = [[MTLRenderPipelineDescriptor alloc] init];
	descriptor.colorAttachments[0].pixelFormat = MTLPixelFormatBGRA8Unorm;
	descriptor.vertexFunction = [library newFunctionWithName:@"VertexFunction"];
	descriptor.fragmentFunction = [library newFunctionWithName:@"FragmentFunction"];
	pipelineState = [device newRenderPipelineStateWithDescriptor:descriptor error:nil];

	displayLink = [self displayLinkWithTarget:self selector:@selector(render)];
	[displayLink addToRunLoop:NSRunLoop.mainRunLoop forMode:NSRunLoopCommonModes];

	return self;
}

- (void)render
{
	if (framebuffer == 0)
	{
		return;
	}

	id<MTLCommandBuffer> commandBuffer = [commandQueue commandBuffer];

	MTLRenderPassDescriptor *descriptor = [MTLRenderPassDescriptor renderPassDescriptor];
	descriptor.colorAttachments[0].texture = framebuffer;
	descriptor.colorAttachments[0].storeAction = MTLStoreActionStore;
	descriptor.colorAttachments[0].loadAction = MTLLoadActionClear;
	descriptor.colorAttachments[0].clearColor = MTLClearColorMake(0.5, 0.5, 0.5, 1);

	id<MTLRenderCommandEncoder> encoder =
	        [commandBuffer renderCommandEncoderWithDescriptor:descriptor];

	[encoder setRenderPipelineState:pipelineState];
	[encoder drawPrimitives:MTLPrimitiveTypeTriangle vertexStart:0 vertexCount:3];
	[encoder endEncoding];

	[commandBuffer commit];
	[commandBuffer waitUntilCompleted];
	self.layer.contents = (__bridge id)framebufferSurface;
}

- (void)viewDidChangeBackingProperties
{
	[super viewDidChangeBackingProperties];
	[self updateFramebuffer];
}

- (void)setFrameSize:(NSSize)size
{
	[super setFrameSize:size];
	[self updateFramebuffer];
}

- (void)updateFramebuffer
{
	NSSize size = [self convertSizeToBacking:self.frame.size];

	if (framebufferSurface != 0)
	{
		CFRelease(framebufferSurface);
	}

	NSDictionary *properties = @{
		(__bridge NSString *)kIOSurfaceWidth : @(size.width),
		(__bridge NSString *)kIOSurfaceHeight : @(size.height),
		(__bridge NSString *)kIOSurfaceBytesPerElement : @4,
		(__bridge NSString *)kIOSurfacePixelFormat : @(kCVPixelFormatType_32BGRA),
	};
	framebufferSurface = IOSurfaceCreate((__bridge CFDictionaryRef)properties);

	MTLTextureDescriptor *descriptor = [[MTLTextureDescriptor alloc] init];
	descriptor.width = (NSUInteger)size.width;
	descriptor.height = (NSUInteger)size.height;
	descriptor.usage = MTLTextureUsageRenderTarget;
	descriptor.pixelFormat = MTLPixelFormatBGRA8Unorm;
	framebuffer = [device newTextureWithDescriptor:descriptor
	                                     iosurface:framebufferSurface
	                                         plane:0];
}

@end