Precise video scrubbing for pointer/pencil

Tusker/Screens/Gallery/VideoControlsViewController.swift

@@ -270,8 +270,13 @@ private class VideoScrubbingControl: UIControl {
     }
     
     override func beginTracking(_ touch: UITouch, with event: UIEvent?) -> Bool {
-        touchStartLocation = touch.location(in: self)
-        scrubbingStartFraction = fractionComplete
+        if touch.type == .pencil || touch.type == .indirectPointer {
+            touchStartLocation = .zero
+            scrubbingStartFraction = 0
+        } else {
+            touchStartLocation = touch.location(in: self)
+            scrubbingStartFraction = fractionComplete
+        }
         
         animator = UIViewPropertyAnimator(duration: 0.1, curve: .linear)
         animator!.addAnimations {
@@ -290,13 +295,20 @@ private class VideoScrubbingControl: UIControl {
         feedbackGenerator!.prepare()
         #endif
         
+        updateScrubbing(for: touch)
+
         return true
     }
     
     override func continueTracking(_ touch: UITouch, with event: UIEvent?) -> Bool {
+        updateScrubbing(for: touch)
+        return true
+    }
+    
+    private func updateScrubbing(for touch: UITouch) {
         guard let touchStartLocation,
               let scrubbingStartFraction else {
-            return false
+            return
         }
         let location = touch.location(in: self)
         let translation = CGPoint(x: location.x - touchStartLocation.x, y: location.y - touchStartLocation.y)
@@ -326,8 +338,6 @@ private class VideoScrubbingControl: UIControl {
             transform = CGAffineTransform(scaleX: 1 + stretchAmount / bounds.width, y: 1 + 0.5 * (1 - stretchFactor))
                 .translatedBy(x: sign(unclampedFractionComplete) * stretchAmount / 2, y: 0)
         }
-        
-        return true
     }
     
     override func endTracking(_ touch: UITouch?, with event: UIEvent?) {