Piece of Utility code to make CGImage from MTLTexture under (BGRA8Unorm)

MTLTexture+Z.swift

//
//	MTLTexture+Z.swift
//	ZKit
//
//	The MIT License (MIT)
//
//	Copyright (c) 2016 Electricwoods LLC, Kaz Yoshikawa.
//
//	Permission is hereby granted, free of charge, to any person obtaining a copy 
//	of this software and associated documentation files (the "Software"), to deal 
//	in the Software without restriction, including without limitation the rights 
//	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 
//	copies of the Software, and to permit persons to whom the Software is 
//	furnished to do so, subject to the following conditions:
//
//	The above copyright notice and this permission notice shall be included in 
//	all copies or substantial portions of the Software.
//
//	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
//	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
//	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
//	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
//	WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//	THE SOFTWARE.
//


import Foundation
import CoreGraphics
import MetalKit
import GLKit
import Accelerate



extension MTLTexture {

	#if os(iOS)
	typealias XImage = UIImage
	#elseif os(macOS)
	typealias XImage = NSImage
	#endif

	var cgImage: CGImage? {

		assert(self.pixelFormat == .bgra8Unorm)
	
		// read texture as byte array
		let rowBytes = self.width * 4
		let length = rowBytes * self.height
		let bgraBytes = [UInt8](repeating: 0, count: length)
		let region = MTLRegionMake2D(0, 0, self.width, self.height)
		self.getBytes(UnsafeMutableRawPointer(mutating: bgraBytes), bytesPerRow: rowBytes, from: region, mipmapLevel: 0)

		// use Accelerate framework to convert from BGRA to RGBA
		var bgraBuffer = vImage_Buffer(data: UnsafeMutableRawPointer(mutating: bgraBytes),
					height: vImagePixelCount(self.height), width: vImagePixelCount(self.width), rowBytes: rowBytes)
		let rgbaBytes = [UInt8](repeating: 0, count: length)
		var rgbaBuffer = vImage_Buffer(data: UnsafeMutableRawPointer(mutating: rgbaBytes),
					height: vImagePixelCount(self.height), width: vImagePixelCount(self.width), rowBytes: rowBytes)
		let map: [UInt8] = [2, 1, 0, 3]
		vImagePermuteChannels_ARGB8888(&bgraBuffer, &rgbaBuffer, map, 0)

		// flipping image virtically
		let flippedBytes = bgraBytes // share the buffer
		var flippedBuffer = vImage_Buffer(data: UnsafeMutableRawPointer(mutating: flippedBytes),
					height: vImagePixelCount(self.height), width: vImagePixelCount(self.width), rowBytes: rowBytes)
		vImageVerticalReflect_ARGB8888(&rgbaBuffer, &flippedBuffer, 0)

		// create CGImage with RGBA
		let colorScape = CGColorSpaceCreateDeviceRGB()
		let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue)
		guard let data = CFDataCreate(nil, flippedBytes, length) else { return nil }
		guard let dataProvider = CGDataProvider(data: data) else { return nil }
		let cgImage = CGImage(width: self.width, height: self.height, bitsPerComponent: 8, bitsPerPixel: 32, bytesPerRow: rowBytes,
					space: colorScape, bitmapInfo: bitmapInfo, provider: dataProvider,
					decode: nil, shouldInterpolate: true, intent: .defaultIntent)
		return cgImage
	}

	var image: XImage? {
		guard let cgImage = self.cgImage else { return nil }
		#if os(iOS)
		return UIImage(cgImage: cgImage)
		#elseif os(macOS)
		return NSImage(cgImage: cgImage, size: CGSize(width: cgImage.width, height: cgImage.height))
		#endif
	}

}

legendary

old but gold 🙇