Ciimage Display Mtkview VS Glkview Performance

Rendering small CIImage centered in MTKView

This is most curious. If you use the "new" CIRenderDestination API instead of context.render(…) it actually works:

let destination = CIRenderDestination(width: Int(view.drawableSize.width),
                                      height: Int(view.drawableSize.height),
                                      pixelFormat: view.colorPixelFormat,
                                      commandBuffer: buffer,
                                      mtlTextureProvider: { () -> MTLTexture in
                                          return drawable.texture
                                      })
try! self.context.startTask(toRender: centered, to: destination)

I don't know why, but context.render(…) doesn't seem to respect the translation of the image or the given bounds. Maybe someone else knows more...

Confusion About CIContext, OpenGL and Metal (SWIFT). Does CIContext use CPU or GPU by default?

I started making this a comment, but I think since WWDC'18 this works best as an answer. I'll edit as others more an expert than I comment, and am willing to delete the entire answer if that's the proper thing to do.

You are on the right track - utilize the GPU when you can and it's a good fit. CoreImage and Metal, while "low-level" technologies that "usually" use the GPU, can use the CPU if that is desired. CoreGraphics? It renders things using the CPU.

Images. A UIImage and a CGImage are actual images. A CIImage however, isn't. The best way to think of it is a "recipe" for an image.

I typically - for now, I'll explain in a moment - stick to CoreImage, CIFilters, CIImages, and GLKViews when working with filters. Using a GLKView against a CIImage means using OpenGL and a single CIContext and EAGLContext. It offers almost as good performance as using MetalKit or MTKViews.

As for using UIKit and it's UIImage and UIImageView, I only do when needed - saving/sharing/uploading, whatever. Stick to the GPU until then.

....

Here's where it starts getting complicated.

Metal is an Apple proprietary API. Since they own the hardware - including the CPU and GPU - they've optimized it for them. It's "pipeline" is somewhat different than OpenGL. Nothing major, just different.

Until WWDC'18, using GLKit, including GLKView, was fine. But all things OpenGL were depricated, and Apple is moving things to Metal. While the performance gain (for now) isn't that great, you may be best off for something new to use MTKView, Metal, and CIContext`.

Look at the answer @matt gave here for a nice way to use MTKViews.

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