Explain the difference between 2D and 3D UI in Unity and when to use each.

• A. There is no difference between 2D and 3D UI.
• B. 2D UI uses screen-space canvases for HUDs and menus; 3D UI uses world-space canvases for in-scene interfaces on objects. Use 3D for in-world interactions, 2D for overlays.
• C. 2D UI is always interactive; 3D UI is not.
• D. 3D UI cannot be used for menus.

Answer: (B)

In Unity, UI can live in two spatial modes: screen-space and world-space. Screen-space UI is rendered as an overlay on the player's screen, so it stays fixed regardless of how the camera moves. This is perfect for HUDs, menus, health bars, and other overlays that should always be readable and independent of the scene’s geometry. World-space UI, on the other hand, exists inside the 3D world as part of the scene. A canvas in world space behaves like a 3D object placed on or around a character or object, so you can interact with it as part of the environment—think control panels on a vehicle, terminals on a wall, or dashboards on machinery.

Use 2D for overlays you want to remain anchored to the screen and, typically, scale with screen size. Use 3D for in-world interfaces that players can approach, look at from angles, or interact with as part of the scene. For interaction, 2D UI uses standard screen-space input, while 3D UI often requires raycasting or other world-space interaction methods to hit the canvas.

The other options aren’t accurate because UI does differ between 2D and 3D, 2D UI isn’t inherently always interactive, and 3D UI can be used for menus when placed in world space.