Change the luminance algorithm so that we don't miss images in unexpected formats. Fixes #2967

Shared/Extensions/IconImage.swift

@@ -63,47 +63,81 @@ final class IconImage {
 fileprivate enum ImageLuminanceType {
 	case regular, bright, dark
 }
+
 extension CGImage {
 
 	func isBright() -> Bool {
-		guard let imageData = self.dataProvider?.data, let luminanceType = getLuminanceType(from: imageData) else {
+		guard let luminanceType = getLuminanceType() else {
 			return false
 		}
 		return luminanceType == .bright
 	}
 	
 	func isDark() -> Bool {
-		guard let imageData = self.dataProvider?.data, let luminanceType = getLuminanceType(from: imageData) else {
+		guard let luminanceType = getLuminanceType() else {
 			return false
 		}
 		return luminanceType == .dark
 	}
 	
-	fileprivate func getLuminanceType(from data: CFData) -> ImageLuminanceType? {
-		guard let ptr = CFDataGetBytePtr(data) else {
-			return nil
-		}
-
-		let length = CFDataGetLength(data)
-		var pixelCount = 0
+	fileprivate func getLuminanceType() -> ImageLuminanceType? {
+		
+		// This has been rewritten with information from https://christianselig.com/2021/04/efficient-average-color/
+		
+		// First, resize the image. We do this for two reasons, 1) less pixels to deal with means faster
+		// calculation and a resized image still has the "gist" of the colors, and 2) the image we're dealing
+		// with may come in any of a variety of color formats (CMYK, ARGB, RGBA, etc.) which complicates things,
+		// and redrawing it normalizes that into a base color format we can deal with.
+		// 40x40 is a good size to resize to still preserve quite a bit of detail but not have too many pixels
+		// to deal with. Aspect ratio is irrelevant for just finding average color.
+		let size = CGSize(width: 40, height: 40)
+		
+		let width = Int(size.width)
+		let height = Int(size.height)
+		let totalPixels = width * height
+		
+		let colorSpace = CGColorSpaceCreateDeviceRGB()
+		
+		// ARGB format
+		let bitmapInfo: UInt32 = CGBitmapInfo.byteOrder32Little.rawValue | CGImageAlphaInfo.premultipliedFirst.rawValue
+		
+		// 8 bits for each color channel, we're doing ARGB so 32 bits (4 bytes) total, and thus if the image is n pixels wide,
+		// and has 4 bytes per pixel, the total bytes per row is 4n. That gives us 2^8 = 256 color variations for each RGB channel
+		// or 256 * 256 * 256 = ~16.7M color options in total. That seems like a lot, but lots of HDR movies are in 10 bit, which
+		// is (2^10)^3 = 1 billion color options!
+		guard let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: 8, bytesPerRow: width * 4, space: colorSpace, bitmapInfo: bitmapInfo) else { return nil }
+		
+		// Draw our resized image
+		context.draw(self, in: CGRect(origin: .zero, size: size))
+		
+		guard let pixelBuffer = context.data else { return nil }
+		
+		// Bind the pixel buffer's memory location to a pointer we can use/access
+		let pointer = pixelBuffer.bindMemory(to: UInt32.self, capacity: width * height)
+		
 		var totalLuminance = 0.0
 		
-		for i in stride(from: 0, to: length, by: 4) {
-			
-			let r = ptr[i]
-			let g = ptr[i + 1]
-			let b = ptr[i + 2]
-			let a = ptr[i + 3]
-			let luminance = (0.299 * Double(r) + 0.587 * Double(g) + 0.114 * Double(b))
-			
-			if Double(a) > 0 {
+		// Column of pixels in image
+		for x in 0 ..< width {
+			// Row of pixels in image
+			for y in 0 ..< height {
+				// To get the pixel location just think of the image as a grid of pixels, but stored as one long row
+				// rather than columns and rows, so for instance to map the pixel from the grid in the 15th row and 3
+				// columns in to our "long row", we'd offset ourselves 15 times the width in pixels of the image, and
+				// then offset by the amount of columns
+				let pixel = pointer[(y * width) + x]
+				
+				let r = red(for: pixel)
+				let g = green(for: pixel)
+				let b = blue(for: pixel)
+				
+				let luminance = (0.299 * Double(r) + 0.587 * Double(g) + 0.114 * Double(b))
+				
 				totalLuminance += luminance
-				pixelCount += 1
 			}
-			
 		}
 		
-		let avgLuminance = totalLuminance / Double(pixelCount)
+		let avgLuminance = totalLuminance / Double(totalPixels)
 		if totalLuminance == 0 || avgLuminance < 40 {
 			return .dark
 		} else if avgLuminance > 180 {
@@ -113,6 +147,18 @@ extension CGImage {
 		}
 	}
 	
+	private func red(for pixelData: UInt32) -> UInt8 {
+		return UInt8((pixelData >> 16) & 255)
+	}
+	
+	private func green(for pixelData: UInt32) -> UInt8 {
+		return UInt8((pixelData >> 8) & 255)
+	}
+	
+	private func blue(for pixelData: UInt32) -> UInt8 {
+		return UInt8((pixelData >> 0) & 255)
+	}
+	
 }