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This page explains the rules that decide where a piece can be placed, what it may snap to, and how its orientation is chosen.

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Build Part placement modes

Each BuildPart has an explicit Placement Policy:

• Surface Only — socket snapping is disabled; placement comes from raycast surfaces.
• Socket Only — a valid socket connection is required.
• Prefer Socket Then Surface — tries socket placement first and falls back to surface placement only when there is no meaningful socket context.

For new content, prefer these explicit policies instead of relying on legacy compatibility flags.

Surface placement

Surface placement is controlled jointly by the shared BuildPlacementSettings and the individual Build Part.

Shared settings

Surface Layers controls which layers can be hit, while Max Distance limits the raycast. The selected Aim Mode controls where the ray originates.

Per-part controls

Important Build Part fields are:

• Allow Grid Snap — opt this piece into grid snapping.
• Allow Surface Rotation — lets player-driven rotation affect free/surface placement.
• Override Surface Rotation Step — replaces the shared rotation increment for this piece.
• Override Grid Snap Value — replaces the shared grid cell size for this piece.
• Align To Surface Normal — aligns the piece to the hit normal for sloped/angled surfaces.
• Allow Place On Surface — permits non-BuildPart geometry such as terrain or static world surfaces.
• Allowed Support Tags — restricts BuildPart-on-BuildPart placement to selected categories.