I’m investigating an issue with simultaneous Apple Pencil and finger input on iPad.
Apple Pencil + finger input works correctly while the Pencil user’s hand/palm is off the display.
However, when drawing naturally with Apple Pencil with the palm resting on the display, an existing finger drawing contact elsewhere on the screen can be cancelled and then stop receiving input for several seconds. Pencil input continues normally throughout.
Initially I suspected PencilKit, but I’ve reproduced the underlying behaviour below PencilKit/SwiftUI. Instrumenting UIKit at UIApplication.sendEvent shows the finger touch being cancelled and, in some cases, no further events for that finger for ~4–5 seconds while Pencil MOVED events continue to arrive normally.
Everything delivered to the application is accounted for, so this appears to occur before our drawing/rendering code.
Is this expected behaviour from the iPad’s Pencil/palm rejection?
More specifically:
- Is there any supported way to tell UIKit that an existing finger contact should remain intentional while Pencil + palm contact is present?
- Is palm rejection configurable at this level?
- Is there another public input API we should be using for this scenario?
We’re currently testing UIEvent.coalescedTouches(for:) to determine whether additional genuine finger samples are available during these apparent gaps, but haven’t completed that test yet.
Any guidance on whether this interaction is expected to be supportable through public UIKit APIs would be appreciated.