Bring gestures, animations and rendering closer to UIKit on iOS by michaelknoch · Pull Request #443 · flowkey/UIKit-cross-platform

michaelknoch · 2026-10-27T15:39:21Z

Type of change: Feature, bug fixes

Motivation (current vs expected behavior)

Brings gesture recognition, animations and layer rendering closer to UIKit on iOS, and adds APIs that were missing.

Gestures follow iOS's state machine: multiple touches, require(toFail:), long press, gestureRecognizerShouldBegin, scroll view deceleration callbacks
New APIs: CAShapeLayer with dashed line paths, UIBezierPath lines, UIView.window and rect conversion (nil is the window), willMove(toSuperview:), UIEvent.touches(for:), location(ofTouch:in:), UILabel.intrinsicContentSize, transform, rect and inset helpers, UIColor(white:alpha:), UIImage.withTintColor, CATransaction timing functions, CALayer.maskedCorners, NSNumber on Android
UIView.center is the layer position
A nested UIView.animate restores the outer animation
contentsCenter draws contents as a nine-slice
Tinted images are rebuilt from PNG data, so they come back after Android loses the GL context
allowsGroupOpacity, on by default as on iOS, composites a translucent subtree once, so overlapping sublayers don't show through each other

Please check if the PR fulfills these requirements

Self-review: I am confident this is the simplest and clearest way to achieve the expected behaviour
There are no dependencies on other PRs or I have linked dependencies through Zenhub
The commit messages are clean and understandable
Tests for the changes have been added (for bug fixes / features)

…leration callbacks - Recognizers get touches before the view, send their action on began, every changed, ended and cancelled, and keep their final state until the touch sequence ends - A recognizer that recognizes cancels the view's touches with touchesCancelled, also when it recognizes as the touch ends - require(toFail:), shouldReceive, gestureRecognizerShouldBegin and simultaneous recognition behave as on iOS - Pans begin after 10pt with a velocity averaged over the last tenth of a second; taps fail when they move or lift with the wrong number of fingers - Add UILongPressGestureRecognizer; UIPinchGestureRecognizer scales from where the fingers started - UIScrollView calls scrollViewDidScroll on every frame of a deceleration and scrollViewDidEndDecelerating when it finishes, its pan stops a deceleration on touch down, and its delegate methods are optional

CAShapeLayer with dashed line paths, UIBezierPath lines, UIView.window, rect conversion with nil as the window, willMove(toSuperview:), UIEvent.touches(for:), location(ofTouch:in:), UILabel.intrinsicContentSize, transform, rect and inset helpers, UIColor(white:alpha:), UIImage.withTintColor, CATransaction timing functions, UIScreen.displayCornerRadius on Android, and @preconcurrency on UIView, UIImage, UIFont and UIScreen

- UIView.center is the layer position - A nested UIView.animate restores the outer animation - contentsCenter draws contents as a nine-slice - Tinted images are rebuilt from PNG data, so they come back after Android loses the GL context - Opt-in allowsGroupOpacity composites a translucent subtree once, so overlapping sublayers don't show through each other

ephemer · 2026-10-27T16:04:58Z


    public var masksToBounds = false

+    /// Off by default, unlike iOS: compositing a fading subtree as one costs an offscreen pass per frame.


but why? we are trying to make our port behave the same as on iOS, so why change the default? if we need to change this for performance reasons we should do it in app code. but even better: we should fix the performance issue

ephemer · 2026-10-27T16:06:16Z

+    /// Where subclasses draw what they add to `contents`, in this layer's coordinates offset by `origin`.
+    func sdlRenderContent(at origin: CGPoint, opacity: Float, renderer: UIScreen) {}


?

to me, the comment doesn't actually explain what this is for. doesn't seem like this would exist in the original API even internally, so do we really need it? why do we want subclasses of this?

ephemer · 2026-10-27T16:06:36Z

    /// returns a non animating copy of the layer
    func createPresentation() -> CALayer {
-        let copy = CALayer(layer: self)
+        let copy = self.copy() as! CALayer


should this be as! Self?

ephemer · 2026-10-27T16:06:48Z

@@ -230,7 +246,7 @@ open class CALayer {

    /// returns a non animating copy of the layer
    func createPresentation() -> CALayer {


should this be -> Self actually?

It's -> Any on iOS (NSObject.copy()), so I'd prefer to keep it the same here.

…undation import

michaelknoch · 2026-10-27T16:07:53Z

+extension UIScreen {
+    /// Android only: the radius of the display's rounded corners, which iOS has no public API for.
+    public var displayCornerRadius: CGFloat {
+        let radius: JavaFloat = (try? jni.call("getDisplayCornerRadius", on: getSDLView())) ?? 0
+        return CGFloat(radius)
+    }
+}


move this to player, its android only API

ephemer · 2026-10-27T16:07:53Z

+        super.init(layer: layer)
+    }
+
+    open override func copy() -> Any {


i think the original API truly does return Any but I don't think anyone will be mad if we make this -> Self instead, which would be my slight preference

ephemer · 2026-10-27T16:09:59Z


+extension CGRect {
+    /// The smallest rect containing all the points, or `.zero` without any.
+    init<Points: Sequence<CGPoint>>(boundingPoints points: Points) {


this is a kind of unusual way to write this. the modern way would be init(boundingPoints points: some Sequence<CGPoint>) I think – should be 100% equivalent but easier to read and reason about?

…rgin

ephemer · 2026-10-27T16:14:05Z

@@ -0,0 +1,17 @@
+#if os(Android)
+public final class NSNumber: ExpressibleByFloatLiteral, ExpressibleByIntegerLiteral {


hmm ok I don't love that we've half implemented this API and that we'd convert Ints to Double. At the extremes this would lose precision in ways that are hard to reason about. I think NSNumber's storage should probably be modelled as an internal enum

public final class NSNumber ... { internal enum Storage { case double(Double), int(Int), float(Float) } }

?

I wouldn't block the PR because of this but I think it might be preferable to not lose numerical precision on large/small ints here.

Also, I think NSNumber really is a class on Apple platforms, but that has potentially dramatic performance downsides. Especially since this is a final class with immutable storage, I would consider writing this as a struct instead – semantically it should be the same, without the potential ref counting and heap allocation footguns

ephemer · 2026-10-27T16:15:39Z

@@ -1,4 +1,4 @@
-@MainActor
+@preconcurrency @MainActor


this needs some explanation I think?

ephemer · 2026-10-27T16:15:57Z

    case cancelled
    case failed
+
+    public static let recognized = UIGestureRecognizerState.ended


ephemer · 2026-10-27T16:16:48Z

+
    public weak var delegate: UIGestureRecognizerDelegate?
-    internal weak var trackedTouch: UITouch?
+    public internal(set) weak var view: UIView?


elsewhere (above) we stopped setting view on the gesture recognizer. not sure if that was intentional or correct?

ephemer · 2026-10-27T16:19:41Z

+        if isSequenceOver {
+            resetToPossible()
+        } else {
+            UIGestureRecognizer.awaitingReset.append(self)


this reads strangely (because it sounds like it's a single recognizer awaiting reset, whereas this is clearly an array or other collection).

…s up with how it's drawn once opaque

ephemer · 2026-10-27T16:20:19Z

 #endif

-@MainActor // UIImage is MainActor but CGImage is not
+@preconcurrency @MainActor // UIImage is MainActor but CGImage is not


this also needs a comment I think?

ephemer · 2026-10-27T16:22:35Z

 }

-@MainActor
+@preconcurrency @MainActor


ephemer · 2026-10-27T16:22:55Z

 }
+
+extension UIScreen {
+    /// Android only: the radius of the display's rounded corners, which iOS has no public API for.


so let's write this #if os(Android)?

i will remove this API entirely from here and add it to our app instead. It does not belong here.

ephemer · 2026-10-27T16:23:44Z

+    private var delayedViewPhases: [UITouchPhase] = []
+
+    /// Hands the touch's current phase to its view, unless a recognizer cancelled it or delays it.
+    func deliverToView() {


this API sounds misleading. it should be something like maybeDeliverToView?

ephemer

Overall it looks good, would be great if you could address/fix the issues raised here wherever possible before merge. Thanks for working on this!

… explain @preconcurrency and sdlRenderContent, and leave UIFont isolated as before

…ncurrency

michaelknoch · 2026-10-27T16:52:20Z

Thanks for the great feedback @ephemer ! I will clean this up before merge

…hickness set, pause deceleration with isDecelerating, and trim comments

…d, border and shadow only round the masked corners as on iOS

michaelknoch requested a review from ephemer as a code owner October 27, 2026 15:39

michaelknoch changed the title ~~Support the new NativePlayer on Android: iOS gesture recognition, the APIs it uses, and the rendering fixes it needs~~ Bring gestures, animations and rendering closer to UIKit on iOS Oct 27, 2026

michaelknoch added 3 commits October 27, 2026 16:57