feat: show outline of windows hidden for privacy reasons (closes #5172)

src/api-wrappers/HelperExtensions.swift

@@ -198,6 +198,15 @@ extension NSImage {
     static func initCopy(_ name: String) -> NSImage {
         return NSImage(named: name)!.copy() as! NSImage
     }
+
+    func tinted(_ color: NSColor) -> NSImage {
+        NSImage(size: size, flipped: false) { rect in
+            color.set()
+            rect.fill()
+            self.draw(in: rect, from: NSRect(origin: .zero, size: self.size), operation: .destinationIn, fraction: 1.0)
+            return true
+        }
+    }
 }
 
 extension CGImage {
@@ -214,6 +223,23 @@ extension CGImage {
     func size() -> NSSize {
         return NSSize(width: width, height: height)
     }
+
+    func iFullyTransparent() -> Bool {
+        guard ![.none, .noneSkipFirst, .noneSkipLast].contains(alphaInfo),
+              let provider = dataProvider, let data = provider.data, let ptr = CFDataGetBytePtr(data)
+        else { return false }
+        // Assumes: kCGImageAlphaPremultipliedFirst | kCGImageByteOrder32Little
+        // Layout: [B, G, R, A]
+        let length = CFDataGetLength(data)
+        var i = 3
+        while i < length {
+            if ptr[i] != 0 {
+                return false
+            }
+            i += 4
+        }
+        return true
+    }
 }
 
 extension CVPixelBuffer {

src/ui/generic-components/LightImageView.swift

@@ -3,6 +3,9 @@ import Cocoa
 /// this is a lightweight view which displays an image using its CALayer
 /// it is an alternative to NSImageView, which doesn't have internal complexities and performance costs
 class LightImageView: NSView {
+    private var outlineLayer: CAShapeLayer!
+    private var handRaisedLayer: CALayer!
+
     required init?(coder: NSCoder) {
         fatalError("Class only supports programmatic initialization")
     }
@@ -25,12 +28,67 @@ class LightImageView: NSView {
             "contentsScale": NSNull()
         ]
         layerContentsRedrawPolicy = .never
+        setupOutlineLayer()
+        setupHandRaisedLayer()
     }
 
+    private func setupOutlineLayer() {
+        outlineLayer = CAShapeLayer()
+        outlineLayer.name = "outline"
+        outlineLayer.fillColor = nil
+        outlineLayer.lineWidth = 1.0
+        outlineLayer.lineDashPattern = [4, 3]
+        outlineLayer.lineCap = .round
+        outlineLayer.lineJoin = .round
+        outlineLayer.isHidden = true
+        layer!.addSublayer(outlineLayer)
+    }
+
+    private func setupHandRaisedLayer() {
+        guard #available(macOS 11.0, *) else { return }
+        handRaisedLayer = CALayer()
+        handRaisedLayer.contentsGravity = .resizeAspect
+        handRaisedLayer.isHidden = true
+        layer!.addSublayer(handRaisedLayer)
+    }
+
+
+    private func updateOutlineLayer(_ fullyTransparent: Bool) {
+        outlineLayer.isHidden = !fullyTransparent
+        guard fullyTransparent else { return }
+        let inset: CGFloat = 0.5
+        let radius: CGFloat = 8.0
+        let bounds = outlineLayer.superlayer!.bounds
+        outlineLayer.frame = bounds
+        let rect = bounds.insetBy(dx: inset, dy: inset)
+        let path = CGPath(roundedRect: rect, cornerWidth: radius, cornerHeight: radius, transform: nil)
+        outlineLayer.path = path
+        outlineLayer.strokeColor = Appearance.fontColor.cgColor
+    }
+
+    private func updateHandRaisedLayer(_ fullyTransparent: Bool) {
+        guard #available(macOS 11.0, *) else { return }
+        handRaisedLayer.isHidden = !fullyTransparent
+        guard fullyTransparent else { return }
+        // we want the icon to be large but not too large, and readable at small sizes
+        let minSize = min(Appearance.iconSize, bounds.width * 0.9, bounds.height * 0.9)
+        let maxSize = Appearance.iconSize * 3
+        let ratio = min(bounds.width / ThumbnailView.maxThumbnailWidth(), bounds.height / ThumbnailView.maxThumbnailHeight())
+        let pointSize = max(minSize, maxSize * ratio)
+        let config = NSImage.SymbolConfiguration(pointSize: pointSize, weight: .regular)
+        guard let image = NSImage(systemSymbolName: "hand.raised.fill", accessibilityDescription: nil)?.withSymbolConfiguration(config) else { return }
+        handRaisedLayer.contents = image.tinted(Appearance.fontColor)
+        handRaisedLayer.bounds = CGRect(x: 0, y: 0, width: pointSize, height: pointSize)
+        handRaisedLayer.position = CGPoint(x: bounds.midX, y: bounds.midY)
+    }
+
+
     func updateContents(_ caLayerContents: CALayerContents, _ size: NSSize) {
+        var fullyTransparent = false
         switch caLayerContents {
         case .cgImage(let image?):
             layer!.contents = image
+            fullyTransparent = image.iFullyTransparent()
         case .pixelBuffer(let pixelBuffer?):
             layer!.contents = CVPixelBufferGetIOSurface(pixelBuffer)?.takeUnretainedValue()
         default: break
@@ -38,6 +96,8 @@ class LightImageView: NSView {
         if frame.size != size {
             frame.size = size
         }
+        updateOutlineLayer(fullyTransparent)
+        updateHandRaisedLayer(fullyTransparent)
     }
 
     func releaseImage() {