Feature/scroll drag events

CHANGELOG.md

@@ -142,6 +142,7 @@ All notable changes to this project will be documented in this file. Take a look
 * Support for displaying Divina (image-based publications like CBZ) in the fixed-layout EPUB navigator.
 * Bitmap images in the EPUB reading order are now supported as a fixed layout resource.
 * Added `offsetFirstPage` preference for fixed-layout EPUBs to control whether the first page is displayed alone or alongside the second page when spreads are enabled.
+* Added `func navigator(_ navigator: any VisualNavigator, didDragBy delta: CGFloat)` and `func navigator(_ navigator: any VisualNavigator, didEndDraggingWithVelocity velocity: CGFloat)` to `VisualNavigatorDelegate`.
 
 #### Streamer
 

Sources/Navigator/EPUB/EPUBNavigatorViewController.swift

@@ -1232,6 +1232,18 @@ extension EPUBNavigatorViewController: EPUBSpreadViewDelegate {
         }
     }
 
+    func spreadView(_ spreadView: EPUBSpreadView, didDragBy delta: CGFloat) {
+        if paginationView?.currentView == spreadView {
+            delegate?.navigator(self, didDragBy: delta)
+        }
+    }
+
+    func spreadView(_ spreadView: EPUBSpreadView, didEndDraggingWithVelocity velocity: CGFloat) {
+        if paginationView?.currentView == spreadView {
+            delegate?.navigator(self, didEndDraggingWithVelocity: velocity)
+        }
+    }
+
     func spreadView(_ spreadView: EPUBSpreadView, present viewController: UIViewController) {
         present(viewController, animated: true)
     }

Sources/Navigator/EPUB/EPUBReflowableSpreadView.swift

@@ -370,6 +370,8 @@ final class EPUBReflowableSpreadView: EPUBSpreadView {
     private var progression: ClosedRange<Double>?
     /// To check if a progression change was cancelled or not.
     private var previousProgression: ClosedRange<Double>?
+    /// Previous scroll offset while the user is dragging.
+    private var previousDragOffset: CGPoint?
 
     /// Called by the javascript code to notify that scrolling ended.
     private func progressionDidChange(_ body: Any) {
@@ -432,8 +434,48 @@ final class EPUBReflowableSpreadView: EPUBSpreadView {
 
     // MARK: - UIScrollViewDelegate
 
+    override func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
+        super.scrollViewWillBeginDragging(scrollView)
+        previousDragOffset = scrollView.contentOffset
+    }
+
     override func scrollViewDidScroll(_ scrollView: UIScrollView) {
         super.scrollViewDidScroll(scrollView)
         setNeedsNotifyPagesDidChange()
+
+        let currentOffset = scrollView.contentOffset
+        if scrollView.isDragging, let previousOffset = previousDragOffset {
+            let delta = progressionDelta(from: previousOffset, to: currentOffset)
+            if delta != 0 {
+                delegate?.spreadView(self, didDragBy: delta)
+            }
+        }
+        previousDragOffset = currentOffset
+    }
+
+    func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
+        delegate?.spreadView(self, didEndDraggingWithVelocity: progressionVelocity(from: velocity))
+        previousDragOffset = nil
+    }
+
+    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
+        previousDragOffset = nil
+    }
+
+    private func progressionDelta(from previousOffset: CGPoint, to currentOffset: CGPoint) -> CGFloat {
+        if viewModel.scroll, !viewModel.verticalText {
+            return currentOffset.y - previousOffset.y
+        }
+
+        let delta = currentOffset.x - previousOffset.x
+        return viewModel.readingProgression == .rtl ? -delta : delta
+    }
+
+    private func progressionVelocity(from velocity: CGPoint) -> CGFloat {
+        if viewModel.scroll, !viewModel.verticalText {
+            return velocity.y
+        }
+
+        return viewModel.readingProgression == .rtl ? -velocity.x : velocity.x
     }
 }

Sources/Navigator/EPUB/EPUBSpreadView.swift

@@ -29,6 +29,12 @@ protocol EPUBSpreadViewDelegate: AnyObject {
     /// Called when the pages visible in the spread changed.
     func spreadViewPagesDidChange(_ spreadView: EPUBSpreadView)
 
+    /// Called continuously while the user drags the content.
+    func spreadView(_ spreadView: EPUBSpreadView, didDragBy delta: CGFloat)
+
+    /// Called when the user lifts their finger after dragging.
+    func spreadView(_ spreadView: EPUBSpreadView, didEndDraggingWithVelocity velocity: CGFloat)
+
     /// Called when the spread view needs to present a view controller.
     func spreadView(_ spreadView: EPUBSpreadView, present viewController: UIViewController)
 

Sources/Navigator/VisualNavigator.swift

@@ -117,6 +117,21 @@ public struct VisualNavigatorPresentation {
     /// Return `true` to navigate to the link, or `false` if you intend to
     /// present the link yourself
     func navigator(_ navigator: VisualNavigator, shouldNavigateToLink link: Link) -> Bool
+
+    /// Called continuously while the user drags the content.
+    ///
+    /// `delta` is the distance in points along the scroll axis since the last
+    /// call. Positive values indicate forward progression through the content.
+    ///
+    /// Not called during momentum deceleration after the user lifts their
+    /// finger.
+    func navigator(_ navigator: any VisualNavigator, didDragBy delta: CGFloat)
+
+    /// Called when the user lifts their finger after dragging.
+    ///
+    /// `velocity` is in points per second along the scroll axis. Positive
+    /// values indicate forward momentum.
+    func navigator(_ navigator: any VisualNavigator, didEndDraggingWithVelocity velocity: CGFloat)
 }
 
 public extension VisualNavigatorDelegate {
@@ -143,4 +158,12 @@ public extension VisualNavigatorDelegate {
     func navigator(_ navigator: VisualNavigator, shouldNavigateToLink link: Link) -> Bool {
         true
     }
+
+    func navigator(_ navigator: any VisualNavigator, didDragBy delta: CGFloat) {
+        // Optional
+    }
+
+    func navigator(_ navigator: any VisualNavigator, didEndDraggingWithVelocity velocity: CGFloat) {
+        // Optional
+    }
 }