World-space UI in Unity: screens in the room, not on the glass

Three render modes, three different problems

Only the third one is the subject of this article, and switching to it changes every assumption in the design: the interface can now be far away, at an angle, behind something, lit, occluded, and viewed from a position the player chooses.

Scale: the canvas is enormous by default

A world-space canvas keeps its width and height in canvas units, so a 1920 by 1080 canvas is 1920 metres wide until you tell it otherwise. The convention that works is to design at pixel dimensions and then scale the canvas down so one canvas unit becomes a small fraction of a metre.

1. Set the RectTransform to your design resolution, for example 1920 by 1080, so the layout inside is authored in familiar numbers.
2. Scale the canvas uniformly to bring it to physical size. A scale of 0.001 turns that canvas into a panel roughly 1.9 metres wide, which is a large wall display.
3. Then think in metres, not pixels. A tablet in the player's hands is about 0.25 metres wide. A weapon display is 0.1. A wall screen is 2 to 3.
4. Keep one scale convention across the project, so components can move between panels without being resized by hand.

Why the text goes soft, and how to fix it

This is the most common complaint about world-space UI and it has three causes that are easy to confuse.

• Not enough texel density. The canvas is scaled down, so a 24-pixel font is being drawn into very few screen pixels. The fix is counter-intuitive: use large font sizes in canvas units and scale the canvas down further, rather than small fonts on a large canvas.
• Dynamic Pixels Per Unit left at 1. On a world-space canvas this controls the resolution at which dynamic elements are rasterised. Raising it sharpens text and dynamic graphics at a memory cost.
• Reference Pixels Per Unit mismatched with your sprites, which makes sliced sprites and borders render at the wrong density and look soft in a different way from the text.
• Use TextMeshPro, always, in world space. Signed distance field text stays crisp across distances and angles in a way bitmap text does not, and it gives you outlines and glow that survive being viewed from three metres away.

Design by angular size, not by pixels

A screen-space element has a fixed size on the display. A world-space element gets smaller as the player walks away, which means legibility is a function of distance, and the design has to declare the distance it is for.

For anything the player approaches and leaves, decide whether it keeps a constant world size (it shrinks with distance, which is realistic) or a constant apparent size (it scales with distance, which is readable). Markers almost always want the second, with a clamp so they never dominate the screen. In VR both of these interact with comfort, which is covered in VR UI/UX design.

Interaction: rays, hands, gaze and the raycaster

A world-space canvas is not clickable by default. It needs a raycaster, and which one depends on how the player is pointing at it.

• The canvas needs a Graphic Raycaster and the scene needs an EventSystem, the same as any other canvas.
• The event camera must be set on the canvas, or hit testing has no idea where the player is looking from. This is the single most common reason a world-space panel does not respond at all.
• In VR or AR, use the XR interaction ray, and give the ray a visible endpoint on the surface. A ray without a cursor is a guess.
• Direct touch needs a collider and forgiveness. Fingers in the air are imprecise, so targets should be physically larger than a mouse would require and separated by more space than a flat screen needs.
• Gaze and dwell need visible progress. If looking at something for a second selects it, the player must see the second passing, and be able to look away to cancel.
• Objects in front of the panel should block it. Without a physics raycaster in the mix, players will click straight through geometry, which reads as a bug even when it is convenient.

Diegetic UI: when the interface belongs to the world

Diegetic interface exists inside the fiction: the display on the weapon, the monitor in the room, the watch on the character's wrist. It is immersive and it is slower to read, so it is a trade, not an upgrade.

1. Use it for information the player consults, not for information they need under pressure. Ammo on the gun works because the gun is already in view. Health on a wall panel does not.
2. Two implementations. A world-space canvas placed on the object, or a camera rendering to a render texture applied to the object's material. The canvas is simpler and better for interaction; the render texture is better when the surface is curved, animated, or needs to be a material property.
3. Give it a reason to exist in the fiction. A screen with no housing, no bezel, no light and no wear reads as an overlay that got lost.
4. Keep a non-diegetic fallback for critical information and for accessibility. Some players cannot read a panel angled away from them, and some panels are occluded by whatever the level designer put in front of them.
5. The FireFall HUD study sits on this line: what belongs in the world, what has to stay on the glass, and why moving something from one to the other changes how fast it can be read.

Lighting, depth and things in the way

Once interface is in the scene, the scene happens to it. This is where world-space UI starts looking wrong in ways that are hard to name.

• Use unlit materials for anything that must stay legible. A lit canvas goes dark in a dark room, which is realistic and unreadable.
• Decide about occlusion deliberately. Interface that draws through walls is useful for markers and wrong for terminals. That is a depth-test decision, and it should be made per element type rather than globally.
• Sorting between panels and transparent scene objects is a real problem. Smoke, glass and particles will interleave with your canvas in ways that vary by camera angle.
• Angle panels towards the player rather than leaving them flat on a wall the player approaches from the side. A panel read at forty-five degrees loses most of its legibility.
• Beware of glow in dark scenes. Additive interface elements bloom aggressively and turn text into a smear at exactly the distance the player reads it from.

Screen-space interface competes with the game for attention. World-space interface competes with the room for light, angle and distance.

Performance in world space

• Every world-space canvas is its own rendering and rebuild unit, so the same change-rate rules apply as anywhere else: keep the animating parts on a small canvas of their own. See why your Unity menus tank the frame rate.
• Cull by distance. A panel nobody can read at thirty metres does not need to be updating.
• Reduce update rate with distance. A terminal across the room can refresh a few times a second instead of every frame.
• Render textures are not free. Each one is a camera rendering a scene. Update them on demand rather than continuously where the content is mostly static.
• In VR everything is drawn twice. Interface cost is doubled, and the frame budget is the tightest of any platform you ship on.

uGUI or UI Toolkit for world space

This has changed recently and is worth checking rather than assuming. Unity's current comparison of UI systems lists world-space UI and VR under UI Toolkit, alongside multi-resolution menus and UI needing custom shaders and materials. uGUI keeps in-scene authoring, serialized events and Animation Clip integration, none of which UI Toolkit has.

• Choose uGUI when the interface is attached to scene objects and you want to place and preview it in the scene, or when it is animated with clips and Timeline.
• Choose UI Toolkit when the panel is a dense data screen, when you want custom shaders and vector graphics on it, or when the rest of your interface is already there.
• Check the manual for your Unity version before committing, because this specific page is one of the ones that changes between releases. The wider decision is in uGUI or UI Toolkit.

Before it ships

1. Stand at the closest and furthest distance the player can read the panel from. Is it legible at both?
2. Approach it from the side. At what angle does it stop working?
3. Look at it in your darkest scene and your brightest one.
4. Put an object between the player and the panel. Does the interaction still behave the way you intended?
5. Check the event camera is assigned on every world-space canvas.
6. In VR, check it at seated and standing height, and with the player standing too close.
7. Turn off every light in the scene. Anything that vanished is lit when it should be unlit.
8. Profile with every world-space panel in the level visible at once.
9. Read every string at the furthest supported distance, in the smallest supported headset resolution or the lowest supported display resolution.
10. Confirm there is a non-diegetic route to any information a player must have.