iOS AR 3D Drawing Feature

I need a lightweight, proof-of-concept AR function for an iOS app. Using the iPhone’s camera, the user should be able to draw simple 3D strokes that stay anchored in real space as they move the device—similar to “air doodling.” A clean, minimal interface is fine; the emphasis is on getting the core drawing logic working smoothly.

Key requirements
• Platform: iOS (ARKit is the natural fit, but I’m open to SceneKit or a compact Unity/AR Foundation setup if you can keep the build size lean).
• Core interaction: track a single finger on the screen and render a colored polyline or tube in 3D space at that position.
• Persistence during session: the lines should remain visible from any angle until the user resets.
• Deliverable: Xcode project (or Unity project) with clear comments, ready to run on the latest iOS version.

This is an initial concept, so focus on functionality over polish; no UI chrome or save/export needed. If the prototype feels smooth and stable, there will be follow-up work for gesture refinements and feature expansion.