macOS 27 Sidecar direct touch: UI taps hit the widget under the previous cursor position (canvas unaffected)

Description

macOS 27 / iPadOS 27 added direct finger touch to Sidecar. In Aseprite, finger taps on UI elements (menus, palette, buttons, timeline) are delivered to the widget located under the previous mouse cursor position instead of the tapped location. Drawing on the canvas with a finger works correctly.

Steps to reproduce

1. Connect an iPad via Sidecar (macOS 27 + iPadOS 27).
2. Move Aseprite's window to the iPad display.
3. Place the mouse cursor over any UI element (e.g. a palette color).
4. Tap a different UI element with a finger on the iPad.

Expected

The tapped element is activated.

Actual

The element under the previous cursor position is activated.

System

• Aseprite: v1.3.18.6
• macOS 27.0, MacBook Air M5
• iPadOS 27.0, iPad mini 6
• Connection: wireless

Notes

• Canvas input via finger touch works correctly (strokes land where tapped).
• Apple Pencil works correctly everywhere, including the UI.
• Native apps (e.g. Safari) handle the same touch input correctly, including multi-finger gestures, so Sidecar itself seems to deliver correct coordinates.
• Hypothesis: a touch generates a mouse-down at the new position without a preceding mouse-move, and the UI hit-testing relies on the last known hover state rather than the event's own coordinates. Synthesizing a mouse-move before handling the click may fix it.
• Possibly related to how Sidecar-synthesized input is handled (cf. #2722).