1 files changed, 34 insertions, 0 deletions

diff --git a/src/macos/Sources/PardesView.swift b/src/macos/Sources/PardesView.swift
index 5df1fd73..ba3677e7 100644
--- a/src/macos/Sources/PardesView.swift
+++ b/src/macos/Sources/PardesView.swift
@@ -1842,6 +1842,20 @@ final class PardesView: NSView {
         fed()
     }
 
+    /// Fingers down and fingers up on a precise scroll. Entry points of their
+    /// own for the same reason rotateEnd is one: NSEvent phases have no public
+    /// constructor, and a fling nothing can synthesize is a fling nothing can
+    /// assert.
+    func scrollBegin() {
+        pardes_scroll_begin()
+        fed()
+    }
+
+    func scrollEnd() {
+        pardes_scroll_end()
+        fed()
+    }
+
     func rotate(degrees: CGFloat) {
         guard degrees != 0 else { return }
         pardes_rotate(Float(degrees))
@@ -2086,12 +2100,32 @@ final class PardesView: NSView {
             return
         }
         if event.hasPreciseScrollingDeltas {
+            // Phases first: a finger back on the pad has to catch a coast before
+            // its own travel is spent, or the first millimetre of the new swipe
+            // would be added to the old fling instead of replacing it.
+            //
+            // Momentum events carry `phase == .none` and a momentumPhase
+            // instead, so neither branch here fires for them — they are just
+            // more travel, and libpardes lets them take the gesture over. That
+            // is deliberate: AppKit's fling is the one the rest of the system
+            // uses, and a second fling of our own underneath it would scroll
+            // everything at double speed. `pardes_scroll_end` exists for the
+            // devices AppKit does NOT fling for.
+            if event.phase == .began { scrollBegin() }
             // The core scrolls a cell at a time, so libpardes accumulates the
             // sub-cell travel and spends it as wheel presses — which is why the
             // cell has to travel with the delta.
             scroll(rows: -event.scrollingDeltaY / cellHeight,
                    cols: -event.scrollingDeltaX / cellWidth,
                    at: at)
+            switch event.phase {
+            case .ended: scrollEnd()
+            // A gesture the system took away should not be thrown. scrollBegin
+            // is the catching half of the pair — coast stopped, bank and
+            // velocity cleared — which is exactly what a cancellation means.
+            case .cancelled: scrollBegin()
+            default: break
+            }
         } else {
             // AppKit's sign is the opposite of the DOM's: positive deltaY means the
             // content moved down, which is a scroll back through history.