feat: two finger swipe to change brightness

ImageViewer/ViewController.swift

@@ -50,7 +50,7 @@ struct LocalState: Codable {
     var backgroundColor: String = "black"
 }
 
-class ViewController: UIViewController, UIGestureRecognizerDelegate {
+final class ViewController: UIViewController, UIGestureRecognizerDelegate {
     let metadataFilename = "metadata.fb"
 
     var homeView = UIView()
@@ -62,6 +62,9 @@ class ViewController: UIViewController, UIGestureRecognizerDelegate {
 
     var pendingAlert: UIAlertController?
 
+    var initialBrightness: CGFloat = 0
+    let dragRangeForFullBrightness: CGFloat = 300
+
     var imageView = UIImageView()
     var mode = PageTurnMode.leftToRight
     var metadataList: [URL: Metadata] = [:]
@@ -794,6 +797,11 @@ class ViewController: UIViewController, UIGestureRecognizerDelegate {
         swipeRight.direction = .right
         readerView.addGestureRecognizer(swipeRight)
 
+        let pan = UIPanGestureRecognizer(target: self, action: #selector(handlePan(_:)))
+        pan.minimumNumberOfTouches = 2
+        pan.maximumNumberOfTouches = 2
+        readerView.addGestureRecognizer(pan)
+
         setupTapZones()
     }
 
@@ -1303,6 +1311,20 @@ class ViewController: UIViewController, UIGestureRecognizerDelegate {
         }
     }
 
+     @objc private func handlePan(_ gesture: UIPanGestureRecognizer) {
+        switch gesture.state {
+        case .began:
+            initialBrightness = UIScreen.main.brightness
+        case .changed:
+            let translation = gesture.translation(in: view)
+            let delta = -translation.y / dragRangeForFullBrightness
+            let newBrightness = initialBrightness + delta
+            UIScreen.main.brightness = min(max(newBrightness, 0.0), 1.0)
+        default:
+            break
+        }
+    }
+
     func setupImageView() {
         imageView.translatesAutoresizingMaskIntoConstraints = false
         // Scaling is done when the image is loaded to avoid scaling on main thread