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Passthrough

Passthrough allows users to have more awareness of the physical environment; however, it is not equivalent to natural human vision. HMDs have limited field of view (FoV) and are not as accurate at representing important visual cues like depth and color. In this guidance, we define virtual content as any rendered asset that is not provided by passthrough.

The following sections discuss considerations for the activity space, placement of virtual objects (occlusions), and duration of exposure when considering user comfort and safety.

Activity space

Unlike fully immersive experiences where users are immersed within a clear, predefined activity space, mixed reality allows users to bring their physical world into the virtual experience via passthrough. Scene information helps the experience feel more immersive by constraining virtual content within a room and its physical objects via real-world physics and depth ordering. Importantly, however, neither scene nor passthrough is a substitute for the safety mechanisms provided by the boundary.

Within a boundary

Boundary (formerly known as guardian) instructs users to clear their activity space prior to play and to avoid potential challenges in immersive experiences. Boundary provides a just-in-time warning when users approach the edge of their cleared space, even when not in view (e.g., backing up).

Figure 1: The boundary grid appears when users approach the edge of their defined activity space, providing a visual warning. Importantly, it also appears if they are near an edge outside their FoV.

Avoid placing content that users will closely interact with near the boundary to minimize the chance of unintended contacts with objects outside the Boundary.
Do not instruct users to draw a boundary outside their walls or other usable space.
Content should not spawn outside the boundary when in use.

Scene without a boundary

Mixed reality blends the physical with the virtual in areas with furniture, objects, and other people. Scene allows users to mark walls and furniture within the activity space. This constrains virtual content within walls and avoid intersections with marked furniture.

Disabling the boundary allows users to explore more of the room. As an area may not have been cleared, there may be more clutter.
There is no warning when leaving the room; users only enter full passthrough.
We still recommend user education on clearing the activity space of floor-level clutter, avoiding unlevel surfaces (e.g., stairs, ramps), and not placing fragile items on surfaces used in MR.
MR identification is an optional feature that provides warnings near marked objects, but only when they are in close proximity to the user.

No boundary or scene

Without boundary or scene knowledge about the physical environment, virtual content can violate user expectations and lead to challenges.

Virtual content can appear to spawn outside the designated activity space, outside a user’s physical space, and intersect with physical objects.
Depth API by itself is not sufficient to solve these issues because when it is active, content outside physical walls will become invisible (i.e., occluded by the walls).
It also does not support moving virtual content rebounding off physical objects – this can defy user expectations by allowing virtual content to pass through or disappear behind physical objects.
A reasonable use case is minimal content that is intentionally placed by the user; it is not recommended for dynamic content, user-locked content, or apps that demand high user locomotion.

Figure 2: Boundary keeps virtual content within the activity space predefined by the user

Figure 3: Scene without a boundary allows users to move around the entire room. Some furniture may not be marked, allowing virtual content to intersect with unmarked objects.

Figure 4: With no boundary or scene, virtual content can spawn anywhere, even outside the room. With Depth API, content outside the walls is invisible to the user. With nothing, virtual content will be visible but unreachable beyond the walls.

Duration of exposure

Long periods of exposure to mixed reality or full passthrough may result in visual discomfort, motion sickness, disorientation, or negative after-effects.
Users should be encouraged to take intermittent breaks. If they feel discomfort, they should not start again until they no longer feel discomfort.

Next steps

For more health and safety API specific info and general considerations, see the following:

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