Fix sometimes broken masking of text view link preview animations

Tusker.xcodeproj/project.pbxproj

@@ -178,6 +178,7 @@
 		D68E525B24A3D77E0054355A /* TuskerRootViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D68E525A24A3D77E0054355A /* TuskerRootViewController.swift */; };
 		D68E525D24A3E8F00054355A /* SearchViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D68E525C24A3E8F00054355A /* SearchViewController.swift */; };
 		D68FEC4F232C5BC300C84F23 /* SegmentedPageViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D68FEC4E232C5BC300C84F23 /* SegmentedPageViewController.swift */; };
+		D690797324A4EF9700023A34 /* UIBezierPath+Helpers.swift in Sources */ = {isa = PBXBuildFile; fileRef = D690797224A4EF9700023A34 /* UIBezierPath+Helpers.swift */; };
 		D693DE5723FE1A6A0061E07D /* EnhancedNavigationViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D693DE5623FE1A6A0061E07D /* EnhancedNavigationViewController.swift */; };
 		D693DE5923FE24310061E07D /* InteractivePushTransition.swift in Sources */ = {isa = PBXBuildFile; fileRef = D693DE5823FE24300061E07D /* InteractivePushTransition.swift */; };
 		D6945C2F23AC47C3005C403C /* SavedDataManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6945C2E23AC47C3005C403C /* SavedDataManager.swift */; };
@@ -490,6 +491,7 @@
 		D68E525A24A3D77E0054355A /* TuskerRootViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TuskerRootViewController.swift; sourceTree = "<group>"; };
 		D68E525C24A3E8F00054355A /* SearchViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SearchViewController.swift; sourceTree = "<group>"; };
 		D68FEC4E232C5BC300C84F23 /* SegmentedPageViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SegmentedPageViewController.swift; sourceTree = "<group>"; };
+		D690797224A4EF9700023A34 /* UIBezierPath+Helpers.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "UIBezierPath+Helpers.swift"; sourceTree = "<group>"; };
 		D693DE5623FE1A6A0061E07D /* EnhancedNavigationViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = EnhancedNavigationViewController.swift; sourceTree = "<group>"; };
 		D693DE5823FE24300061E07D /* InteractivePushTransition.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = InteractivePushTransition.swift; sourceTree = "<group>"; };
 		D6945C2E23AC47C3005C403C /* SavedDataManager.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SavedDataManager.swift; sourceTree = "<group>"; };
@@ -1073,6 +1075,7 @@
 				D6EBF01623C55E0D00AE061B /* UISceneSession+MastodonController.swift */,
 				D6969E9D240C81B9002843CE /* NSTextAttachment+Emoji.swift */,
 				D67895BB24671E6D00D4CD9E /* PKDrawing+Render.swift */,
+				D690797224A4EF9700023A34 /* UIBezierPath+Helpers.swift */,
 			);
 			path = Extensions;
 			sourceTree = "<group>";
@@ -1870,6 +1873,7 @@
 				D667E5E721349D4C0057A976 /* ProfileTableViewController.swift in Sources */,
 				D6D4DDD0212518A000E1C4BB /* AppDelegate.swift in Sources */,
 				D6B053A423BD2C8100A066FA /* AssetCollectionsListViewController.swift in Sources */,
+				D690797324A4EF9700023A34 /* UIBezierPath+Helpers.swift in Sources */,
 				D693DE5723FE1A6A0061E07D /* EnhancedNavigationViewController.swift in Sources */,
 				D6163F2C21AA0AF1008DAC41 /* MyProfileTableViewController.swift in Sources */,
 			);

Tusker/Extensions/UIBezierPath+Helpers.swift

@@ -0,0 +1,61 @@
+//
+//  UIBezierPath+Helpers.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 6/25/20.
+//  Copyright © 2020 Shadowfacts. All rights reserved.
+//
+
+import UIKit
+
+// TODO: write unit tests for this
+extension UIBezierPath {
+    
+    /// Create a new UIBezierPath that wraps around the given array of rectangles.
+    /// This is not a convex hull aglorithm. What this does is it takes a set of rectangles
+    /// and draws a line around the outer borders of the combined shape.
+    convenience init(wrappingAround rects: [CGRect]) {
+        precondition(rects.count > 0)
+        let rects = rects.sorted { $0.minY < $1.minY }
+        
+        self.init()
+        
+        // start at the top left corner
+        self.move(to: CGPoint(x: rects.first!.minX, y: rects.first!.minY))
+        
+        // walk down the left side
+        var prevLeft = rects.first!.minX
+        for rect in rects where !rect.minX.isEqual(to: prevLeft) {
+            self.addLine(to: CGPoint(x: prevLeft, y: rect.minY))
+            self.addLine(to: CGPoint(x: rect.minX, y: rect.minY))
+            prevLeft = rect.minX
+        }
+        
+        // ensure at the bottom left if not already
+        let bottomLeft = CGPoint(x: rects.last!.minX, y: rects.last!.maxY)
+        if !self.currentPoint.equalTo(bottomLeft) {
+            self.addLine(to: bottomLeft)
+        }
+        
+        // across the bottom of the last rect
+        self.addLine(to: CGPoint(x: rects.last!.maxX, y: rects.last!.maxY))
+        
+        // walk up the right side
+        var prevRight = rects.last!.maxX
+        for rect in rects.reversed() where !rect.maxX.isEqual(to: prevRight) {
+            self.addLine(to: CGPoint(x: prevRight, y: rect.maxY))
+            self.addLine(to: CGPoint(x: rect.maxX, y: rect.maxY))
+            prevRight = rect.maxX
+        }
+        
+        // ensure at the top right if not already
+        let topRight = CGPoint(x: rects.first!.maxX, y: rects.first!.minY)
+        if !self.currentPoint.equalTo(topRight) {
+            self.addLine(to: topRight)
+        }
+        
+        // across the top of the first rect
+        self.addLine(to: CGPoint(x: rects.first!.minX, y: rects.first!.minY))
+    }
+    
+}

Tusker/Views/ContentTextView.swift

@@ -327,7 +327,13 @@ extension ContentTextView: UIContextMenuInteractionDelegate {
         
         // The preview parameters describe how the preview view is shown inside the prev.
         let parameters = UIPreviewParameters(textLineRects: rectsInCoordinateSpaceOfEnclosingRect as [NSValue])
-        // todo: parameters.visiblePath around text
+        
+        // Mask the snapshot layer to only show the text of the link, and nothing else.
+        // By default, the system-applied mask is too wide and other content may seep in.
+        let path = UIBezierPath(wrappingAround: rectsInCoordinateSpaceOfEnclosingRect)
+        let maskLayer = CAShapeLayer()
+        maskLayer.path = path.cgPath
+        snapshot.layer.mask = maskLayer
         
         // The center point of the the minimum enclosing rect in our coordinate space is the point where the
         // center of the preview should be, since that's also in this view's coordinate space.
@@ -336,7 +342,12 @@ extension ContentTextView: UIContextMenuInteractionDelegate {
         // The preview target describes how the preview is positioned.
         let target = UIPreviewTarget(container: self, center: rectsCenter)
         
-        return UITargetedPreview(view: snapshot, parameters: parameters, target: target)
+        // Create a dummy containerview for the snapshot view, since using a view with a CALayer mask and UIPreviewParameters(textLineRects:)
+        // causes the mask to be ignored. See FB7832297
+        let snapshotContainer = UIView(frame: snapshot.bounds)
+        snapshotContainer.addSubview(snapshot)
+        
+        return UITargetedPreview(view: snapshotContainer, parameters: parameters, target: target)
     }
     
     func contextMenuInteraction(_ interaction: UIContextMenuInteraction, willPerformPreviewActionForMenuWith configuration: UIContextMenuConfiguration, animator: UIContextMenuInteractionCommitAnimating) {