Technical Specification for VR Game Development
Technical spec for VR game — one of most complex documents in gamedev. Problem not in volume, but in specificity: most spec templates written for web apps or regular games and don't cover VR-specifics. Team receiving such spec forced to invent details on fly — and these "invented" details become reworks at late stages.
What's mandatory in VR spec absent in regular spec
Interaction Model section — detailed description of all interaction mechanisms. Not "player picks up items", but "on right or left hand entering 10 cm trigger zone object displays highlight outline (color #FFE066, thickness 2 mm in world space). On Grip Button press object attaches to [right/left hand palm] attach point, with 0.1 s transition animation. On Grip Button release with velocity < 0.5 m/s object stays. With velocity ≥ 0.5 m/s — physics throw with inherited controller velocity".
This detail level seems excessive until developer starts implementation and asks ten questions, each delaying sprint.
Platform matrix — table for each platform (Meta Quest 2, Quest 3, Steam VR, PICO 4): input method (controllers / hand tracking / keyboard), minimum OS/firmware version, required SDK (OpenXR / OVR / SteamVR), supported features (passthrough, spatial anchors, eye tracking).
Comfort Requirements — section most often skipped. Here fixed: allowed locomotion types, vignette parameters (enabled by default, can disable), maximum camera rig angular velocity at snap turn, minimum high framerate target (72/90/120 Hz depending platform), content list requiring motion sickness warning.
Performance Requirements — concrete numbers, not "high performance". For Meta Quest 3: target framerate 90 fps, max draw calls per frame 250, GPU time budget < 11 ms, memory budget 3.5 GB. For SteamVR (PC): minimum GPU — RTX 2060, target 90 fps, reprojection shouldn't activate in normal situation.
VR project spec structure
Good VR game spec includes following sections:
1. Project and Platform Overview. Brief description, target platforms, minimum system requirements, target audience, rating.
2. Technical Stack. Unity version (specific number like 2023.2.x LTS), XR Plugin Management config, used SDKs (OpenXR, Meta XR SDK, SteamVR Plugin), third-party packages.
3. Interaction Model Document. All interactions with detail at "condition → action → feedback" level.
4. Locomotion Specification. Movement types, comfort settings parameters, boundary violation handling.
5. Scene Requirements. For each scene: play area size, object count estimate, lighting approach (baked / realtime / mixed), audio setup.
6. Performance Budget. By platform: framerate, draw calls, poly count, texture memory, shadow casting lights count.
7. Audio Specification. 3D audio engine (Unity AudioSource / FMOD / Wwise), spatial audio approach, haptic feedback mapping.
8. Multiplayer / Networking (if applicable): topology, sync rate, latency requirements, state reconciliation approach.
9. Save System. What saves, format, migration on version update.
10. QA Requirements. Acceptance criteria for each mechanic, test cases for critical scenarios.
Best practices for writing
Most common spec error for VR — describing what user sees, not how it works. "Player hand physically interacts with lever" — not spec. Spec: "On hand entering lever trigger zone XRGrabInteractable activates. Lever moves along Y axis in range -30° to +30° relative pivot point. Current angle transmitted through event OnLeverAngleChanged(float angle). At angle > 25° GameEvent LeverActivated activates. Physics: Rigidbody with angular drag 2.0, no gravity".
Spec work includes iterations with team: first draft based on concept and brief, then technical review with developers (identify unrealizable or conflicting requirements), then final version with acceptance criteria.
| Project Volume | Timeline |
|---|---|
| MVP / prototype (3–5 mechanics) | 1–2 weeks |
| Full game (10–20 mechanics, 1–2 platforms) | 3–5 weeks |
| Multiplatform project with multiplayer | 5–8 weeks |
Cost calculated after concept analysis and project requirements.