Figure 1: The Reality Stack I/O example, implemented with Unity, consists of a 2D user interface ( 1), a 3D sketching tool (2), and a virtual-to-physical surface alignment technique (3ViSuAl [4]). In this scenario, the user operates a Meta Quest Pro device, interacting via controllers (3, 4), hand tracking (5, 6), and eye tracking. Pressing the orange passthrough UI button switches between VR (3, 5) and VST AR (4, 6). The 3D sketching tool enables basic drawings (2), and 3ViSuAl makes it easy to align virtual surfaces with flat physical surfaces. Here, the user has aligned the 2D user interface with a wall, allowing for direct touch interaction (7).