mac/vulkan: log colorspace changes of metal layer

since we have a mapping layer between vulkan and metal (MoltenVK) we
don't actually know which colorspace is used/mapped to.

log colorspace changes to actually see which colorspace was chosen.

osdep/mac/swift_extensions.swift

@@ -136,3 +136,17 @@ extension MTLPixelFormat {
         return "raw pixel format " + String(self.rawValue)
     }
 }
+
+extension CGColorSpace {
+    public var longName: String {
+        let description = String(describing: self)
+        guard let colorSpaceName = self.name as? String,
+              let regex = try? NSRegularExpression(pattern: ".*\\((.*)\\)", options: .caseInsensitive),
+              let result = regex.firstMatch(in: description, options: [], range: NSRange(location: 0, length: description.count)),
+              let range = Range(result.range(at: 1), in: description) else { return description }
+
+        let nameList = description[range].components(separatedBy: "; ").filter { !$0.hasPrefix("kCGColorSpace") }
+        let simpleName = colorSpaceName.replacingOccurrences(of: "kCGColorSpace", with: "")
+        return "\(simpleName) (\(nameList.joined(separator: ", ")))"
+    }
+}

video/out/mac/metal_layer.swift

@@ -41,11 +41,23 @@ class MetalLayer: CAMetalLayer {
         }
     }
 
+    // workaround for nil to none-nil values, oldValue is same as current in those cases
+    var previousColorspace: CGColorSpace?
+    override var colorspace: CGColorSpace? {
+        didSet {
+            if colorspace != previousColorspace {
+                log.verbose("Metal layer colorspace changed: \(colorspace?.longName ?? "nil")")
+            }
+            previousColorspace = colorspace
+        }
+    }
+
     init(common com: MacCommon) {
         common = com
         super.init()
 
         pixelFormat = .rgba16Float
+        previousColorspace = colorspace
         backgroundColor = NSColor.black.cgColor
     }