3D World Building

Expert guidance for level design with GridMaps, CSG bake, and occlusion — not lighting/atmosphere authorship.

NEVER Do

• NEVER forget to bake GridMap navigation — GridMaps don't auto-generate navigation meshes. Use EditorPlugin or manual NavigationRegion3D.
• NEVER use CSG for final game geometry — CSG is for prototyping. Convert to static meshes for performance (use "Bake CSG Mesh" in editor).
• NEVER scale GridMap cell size after placing tiles — Changing cell_size doesn't update existing tiles, causing misalignment. Set it once at the start.
• NEVER ship a MeshLibrary item without verifying collision — Call mesh_library.get_item_shapes(tile_index) (or inspect the source scene StaticBody3D + CollisionShape3D) before convert; empty shapes spawn visual-only geometry players fall through.
• NEVER bake CSG before the combiner has a settled frame — Extract meshes only after await get_tree().process_frame (see safe_csg_baking.gd); baking mid-recompute yields empty or stale ArrayMesh data. Order: finish boolean edits → wait one frame → bake → delete CSG → add collision.
• NEVER animate CSG nodes during gameplay — Moving a CSG node within another forces the CPU to recalculate the boolean geometry, causing significant performance drops.
• NEVER place generic logic nodes in a GridMap — GridMap is highly optimized only for meshes, navigation, and collision. Use proxy tiles + scripts for spawns/triggers.
• NEVER use non-manifold meshes in CSG — Custom CSGMesh3D assets must be manifold (closed, no self-intersections). Non-manifold meshes break the CSG algorithm.

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Available Scripts

MANDATORY: Read the appropriate script before implementing the corresponding pattern. Do NOT Load lighting/sky/fog scripts or deep Environment tutorials here — route to godot-3d-lighting.

collision_gen.gd

Automatic collision shape generation from meshes. Use when importing models without collision or for procedural geometry.

gridmap_runtime_builder.gd

Sole streaming / runtime GridMap entry — batch tile placement, chunk-style rebuilds, and auto-navigation baking. Prefer this over ad-hoc WorldStreamer stubs.

csg_bake_tool.gd

EditorScript to bake CSG geometry to static meshes with proper materials and collision. Use when finalizing level prototypes.

safe_csg_baking.gd

Expert technique for safe CSG baking. Awaits the end of the frame before extracting baked meshes to avoid empty data.

lod_manager.gd

Level-of-detail switching based on camera distance. Manages mesh swapping and visibility for large outdoor scenes.

occlusion_setup.gd

OccluderInstance3D configuration for manual occlusion culling. Use for indoor levels with many rooms.

grid_map_logic_manager.gd

Proxy-tile pattern: replace invisible MeshLibrary markers with spawn/trigger scenes at _ready, then clear proxy cells.

world_streamer.gd

ResourceLoader.load_threaded_request queue — stutter-free chunk instantiation after background load completes.

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Golden Path (GridMap / CSG / Occlusion)

1. MeshLibrary — Source scene: MeshInstance3D + StaticBody3D/CollisionShape3D → Convert To MeshLibrary → verify get_item_shapes().
2. GridMap — Set cell_size once, place cells, bake NavigationRegion3D. Runtime rebuilds: MANDATORY gridmap_runtime_builder.gd.
3. CSG greybox — Prototype with CSGCombiner3D → MANDATORY safe_csg_baking.gd / csg_bake_tool.gd → delete live CSG.
4. Occlusion / LOD — Indoor rooms: occlusion_setup.gd. Distance swaps: lod_manager.gd.
5. Sky / fog / WorldEnvironment — Out of scope; use peer godot-3d-lighting (keep only a DirectionalLight3D present if volumetric fog is enabled elsewhere).

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GridMap Fundamentals

Setup (compact)

extends GridMap

func _ready() -> void:
    mesh_library = load("res://tilesets/dungeon_library.tres")
    cell_size = Vector3(2, 2, 2)  # Set once; never after tiles exist

Cell API: set_cell_item(pos, index[, orientation]), get_cell_item, INVALID_CELL_ITEM, local_to_map / map_to_local. For batch/runtime placement and nav bake, load gridmap_runtime_builder.gd — do not paste a custom chunk streamer.

Collision verification

var shapes := mesh_library.get_item_shapes(tile_index)
if shapes.is_empty():
    push_error("Tile %d has no collision — fix MeshLibrary source scene" % tile_index)

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CSG Bake Order

1. Finish boolean edits under CSGCombiner3D.
2. await get_tree().process_frame (WHY: CSG dirty flags settle one frame late).
3. Bake to MeshInstance3D + collision via scripts above; remove CSG from exported scenes.
4. Never animate CSG at runtime.

Brush types (Box/Cylinder/Sphere/Polygon) are editor greybox tools only — not shipping geometry.

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Streaming Decision

Need	Action
Runtime GridMap tiles / chunk rebuild + nav bake	MANDATORY gridmap_runtime_builder.gd
Large open-world scene streaming	Peer godot-genre-open-world
Ad-hoc WorldStreamer inline stub	Cut — do not reintroduce incomplete load-from-file TODOs

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Expert Techniques

Spatially Partitioning MultiMeshes

Partition dense props into regional MultiMeshInstance3D nodes so frustum/occlusion can cull whole clusters (single MultiMesh AABB draws everything).

GridMap Logic Proxies

Use invisible proxy tile IDs for spawns/triggers; at _ready, get_used_cells_by_item, instantiate logic scenes, clear proxy cells. Keep logic off the GridMap itself.

Interior-Mapping

For city-scale fake interiors, use a spatial shader on window planes — peer godot-shaders-basics. Do not paste full shader recipes here.

Edge Cases

• No collision: empty get_item_shapes → fix MeshLibrary source.
• CSG z-fight: tiny offset on subtraction brushes before bake.

Deep recipes (on demand)

Topic	Reference / script
GridMap / CSG bake walkthrough	gridmap-and-csg.md
Chunk streaming / procgen rooms	streaming-and-procgen.md
Proxy spawn tiles	grid_map_logic_manager.gd
Threaded chunk load	world_streamer.gd

Reference

Progressive disclosure: open Official Documentation links only when researching a specific API; load Related Skills when routing to a peer domain — do not preload the whole lattice.

Official Documentation

• Using GridMaps — MeshLibrary workflow, cell placement, and when GridMap is the right modular level tool.
• MeshLibrary — item meshes, names, and collision shapes that GridMap instances at runtime.
• CSG tools — boolean prototyping with CSGCombiner3D/primitives and the bake-to-mesh handoff.
• Environment and post-processing — WorldEnvironment, Sky, ProceduralSkyMaterial/PanoramaSkyMaterial, and fog modes.
• Volumetric fog and fog volumes — scattering setup, density/albedo, and why lights are required for visible volumetric fog.
• Occlusion culling — OccluderInstance3D placement and CPU cost tradeoffs for indoor rooms.
• Mesh level of detail (LOD) — importer auto-LOD versus manual mesh swaps for large outdoor levels.
• Visibility ranges — GeometryInstance3D distance fade/hysteresis used by LOD managers.
• Collision shapes (3D) — convex/trimesh/primitive choices for MeshLibrary items and baked CSG.
• Navigation introduction (3D) — NavigationRegion3D baking GridMaps never auto-generate.
• Background loading — ResourceLoader threaded chunk streaming without hitch spikes.
• Using MultiMesh — instancing dense props and why spatial MultiMesh partitions restore culling.

Related Skills

Prerequisites

• godot-project-foundations — scene tree, resources, and import basics before MeshLibrary conversion and WorldEnvironment setup.
• godot-physics-3d — StaticBody3D/CollisionShape3D patterns that must land in MeshLibrary source scenes or players fall through tiles.
• godot-gdscript-mastery — typed GridMap/CSG scripting, signals, and await/process_frame patterns used in bake and runtime builders.

Complements

• godot-3d-lighting — DirectionalLight3D and GI that volumetric fog scatters; pair env with real light setup.
• godot-3d-materials — StandardMaterial3D/ORM on tiles and baked CSG meshes after greybox.
• godot-navigation-pathfinding — bake and update NavigationMesh from GridMap geometry after cell edits.
• godot-shaders-basics — interior-mapping and other spatial tricks for fake building interiors at city scale.
• godot-camera-systems — camera distance drives visibility ranges, LOD swaps, and chunk load radii.
• godot-scene-management — scene packing and threaded load queues for stutter-free world streaming.
• godot-performance-optimization — draw-call budgets, occlusion strategy, and MultiMesh partitioning for large levels.

Downstream / consumers

• godot-procedural-generation — dungeon/terrain generators that write cells into GridMap as the placement backend.
• godot-genre-open-world — chunk streaming, floating origin, and HLOD built on these world-building primitives.
• godot-genre-sandbox — player-driven building and editable voxel/grid worlds that reuse GridMap/CSG bake flows.

Master

• godot-master — library router and mirrored module entry for cross-skill discovery.