Ensure brush strokes include the entire gesture.

SignalMessaging/Views/ImageEditor/ImageEditorBrushViewController.swift

@@ -127,7 +127,7 @@ public class ImageEditorBrushViewController: OWSViewController {
     private var currentStrokeSamples = [ImageEditorStrokeItem.StrokeSample]()
 
     @objc
-    public func handleBrushGesture(_ gestureRecognizer: UIGestureRecognizer) {
+    public func handleBrushGesture(_ gestureRecognizer: ImageEditorPanGestureRecognizer) {
         AssertIsOnMainThread()
 
         let removeCurrentStroke = {
@@ -137,10 +137,9 @@ public class ImageEditorBrushViewController: OWSViewController {
             self.currentStroke = nil
             self.currentStrokeSamples.removeAll()
         }
-        let tryToAppendStrokeSample = {
+        let tryToAppendStrokeSample = { (locationInView: CGPoint) in
             let view = self.canvasView.gestureReferenceView
             let viewBounds = view.bounds
-            let locationInView = gestureRecognizer.location(in: view)
             let newSample = ImageEditorCanvasView.locationImageUnit(forLocationInView: locationInView,
                                                               viewBounds: viewBounds,
                                                               model: self.model,
@@ -162,14 +161,22 @@ public class ImageEditorBrushViewController: OWSViewController {
         case .began:
             removeCurrentStroke()
 
-            tryToAppendStrokeSample()
+            // Apply the location history of the gesture so that the stroke reflects
+            // the touch's movement before the gesture recognized.
+            for location in gestureRecognizer.locations {
+                tryToAppendStrokeSample(location)
+            }
+
+            let locationInView = gestureRecognizer.location(in: canvasView.gestureReferenceView)
+            tryToAppendStrokeSample(locationInView)
 
             let stroke = ImageEditorStrokeItem(color: strokeColor, unitSamples: currentStrokeSamples, unitStrokeWidth: unitStrokeWidth)
             model.append(item: stroke)
             currentStroke = stroke
 
         case .changed, .ended:
-            tryToAppendStrokeSample()
+            let locationInView = gestureRecognizer.location(in: canvasView.gestureReferenceView)
+            tryToAppendStrokeSample(locationInView)
 
             guard let lastStroke = self.currentStroke else {
                 owsFailDebug("Missing last stroke.")

SignalMessaging/Views/ImageEditor/ImageEditorPanGestureRecognizer.swift

@@ -13,7 +13,12 @@ public class ImageEditorPanGestureRecognizer: UIPanGestureRecognizer {
 
     public weak var referenceView: UIView?
 
-    public var locationStart: CGPoint?
+    // Capture the location history of this gesture.
+    public var locations = [CGPoint]()
+
+    public var locationStart: CGPoint? {
+        return locations.first
+    }
 
     // MARK: - Touch Handling
 
@@ -25,12 +30,23 @@ public class ImageEditorPanGestureRecognizer: UIPanGestureRecognizer {
             owsFailDebug("Missing view")
             return
         }
-        locationStart = self.location(in: referenceView)
+        locations.append(location(in: referenceView))
+    }
+
+    @objc
+    public override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
+        super.touchesMoved(touches, with: event)
+
+        guard let referenceView = referenceView else {
+            owsFailDebug("Missing view")
+            return
+        }
+        locations.append(location(in: referenceView))
     }
 
     public override func reset() {
         super.reset()
 
-        locationStart = nil
+        locations.removeAll()
     }
 }