BCG Building Generator — User Guide

Version 1.0.0 · Unity 6 · Built-in Render Pipeline and URP

BCG Building Generator is a procedural building tool for city-filler geometry: low-cost, one-draw-call-per-building background buildings for driving, open-world, and mobile games. All mesh and prefab assets are generated at editor time. The only runtime components are two data-only MonoBehaviours that carry no generation logic: BCG_BuildingZone (an optional district marker on BoxCollider zones) and a hidden BCG_BuildingMarker stamped on every generated building.

Installation
Opening the window
Workflow A — Single building
Workflow B — Variation Row
Workflow C — Street Scatter
Workflow D — Populate Zones
Scene tab — inventory & health
BCG_BuildingZone district component
Archetype reference
Advanced fields
Regenerate All
Fix Materials (Active Pipeline)
Bake UVs (Existing)
Save As Prefab Assets
Pipeline notes
Managing generated output
Package contents

1. Installation

Import the package. All shipped scripts, textures, and the demo scene land under Assets/BCG/BuildingGen/. Generated meshes, prefabs, and materials are written to Assets/BCG/BuildingGen/Generated/ the first time you generate a building.

2. Opening the window

Tools > BoneCracker Games > Building Generator > Building Generator

The same submenu also holds Welcome Window — a quick-start panel that opens automatically the first time the asset is imported.

The window is a single docked panel. Minimum size is 418 × 840 px. There is no Play-Mode dependency — everything runs in the Editor.

Window layout

Mode toolbar (top) — four tabs: Single Building, Street, Zones, and Scene. The first three are generation workflows (below); Scene is a read-only inventory of the buildings already in the open scene (§7).
Body — the fields and actions for the active tab; scrolls independently.
Night Lights — a collapsible global window-glow dial shown in every mode, just above the footer (§12, Night Lights).
Persistent footer — pinned to the bottom in every mode. It carries a live pipeline / material-health badge, a Frame on generate toggle, and six maintenance actions (Fix Materials, Regenerate All, Bake UVs (Existing), Select All, Destroy All, Clean Unused…). The footer flows onto one line on a wide window and wraps across rows when narrow. See §11–§16.

The status badge on the left of the footer shows the active render pipeline and whether the facade materials match it — URP · materials OK / Built-in · materials OK (green dot) or … · materials need Fix (amber dot) when the materials would render pink. It is re-checked about once a second and turns green immediately after Fix Materials.

The Frame on generate toggle (right of the footer badge, persisted per-user) controls whether each generate action also frames the new building(s) in the Scene view; selection happens either way.

3. Workflow A — Single building

Single Building mode — archetype, massing, advanced fields, live preview, and the persistent footer.

Choose an Archetype (Tower / Shop / Apartment / House). Switching archetype applies sensible size presets; all fields remain editable.
Choose a Texture Variant (A – D palette: Light Gray / Brick / Graphite Curtain / White Plaster).
Set Cells X, Cells Z, Floors, and Seed. - Width = Cells X × Cell Width; Depth = Cells Z × Cell Width. - The live Footprint readout below the fields shows the resulting dimensions.
Click Generate + Place In Scene.

The generator writes a mesh asset and a prefab under Generated/ (GUID-stable overwrites), then instantiates the prefab at the scene-view pivot dropped to y = 0. The instance is registered with Undo. (When Save As Prefab Assets is off, the building is placed straight into the scene with no asset written — see §14.)

If that spot would overlap a building you generated earlier, the new building is moved clear automatically — see §16, Managing generated output. In an open area it is placed exactly where you asked.

4. Workflow B — Variation Row

Generates five seeded size/seed variations of the current parameters placed in a row, spaced 8 m apart.

Mix Variants toggle (default on): when on, the row picks a texture variant per item from all four palettes, seeded from the main Seed field. Turning it off locks every item to the currently selected Texture Variant. Either way the rng stream is consumed in the same order, so the building sizes are identical regardless of the toggle — only the materials differ.
Click Generate Variation Row (5).

All five instances share a single Undo entry.

5. Workflow C — Street Scatter

Fills one or both sides of a road with seeded buildings facing the street. Expand the Street Scatter foldout.

Street mode — road settings, weighted archetype mix, and variant mix.

Field	Default	Notes
Scatter Seed	12345	Drives every plot: archetype, size, variant, gap.
Road Length (m)	120	Plots fill +X until this length is reached.
Both Sides	on	Line the opposite side of the road as well.
Road Width (m)	16	Clear carriageway between the two rows.
Gap Range (m)	4 – 10	Random spacing between neighbouring plots.
Tower / Shop / Apartment / House weights	0.35 / 0.30 / 0.35 / 0.25	Relative archetype probability.
Variant Mix (A / B / C / D)	all on	Palettes eligible for this scatter.

Click Generate Street Row. All instances parent under BCG_StreetRow_{seed} (one Undo).

6. Workflow D — Populate Zones

Fills BoxCollider-bounded areas with a seeded block of buildings in alternating rows (front-facing, then back-to-back pairs, like a real city block). Expand the Populate Zones (BoxCollider markers) foldout.

Zones mode — the Zone Fill settings and the Populate / Create Zone Marker actions.

Quick start

In the scene, create a GameObject with a BoxCollider sized over the area to fill. - Or click Create Zone Marker in the foldout; this drops a 40 × 4 × 30 m marker at the scene-view pivot, already carrying a BCG_BuildingZone component.
Select the marker object(s).
Set Zone Seed (or leave 0 to auto-assign), Edge Margin, and Row Gap range.
Click Populate Selected Zones.

Field	Default	Notes
Zone Seed	24680	Per-zone seeds derive from this. A non-zero seed on the district component overrides it.
Edge Margin (m)	1	Buildings keep this distance from zone bounds.
Row Gap (m)	6 – 10	Random alley/street width between building rows.
Markers After	Disable	What happens to each zone marker once its area is filled (the buildings live in their own object either way). Disable keeps the marker but switches off its `BoxCollider`, so the bounds stay readable and a repopulate / Clear Output still works. Delete removes the marker GameObject entirely.

Populate Selected Zones — fills every BoxCollider (or BCG_BuildingZone marker) in the selection.
Create Zone Marker — drops a ready-to-size 40 × 30 m district marker at the scene-view pivot.
Populate All In Scene — finds every BCG_BuildingZone in the open scene (including inactive) and repopulates each with its own district settings. Asks for confirmation when there are more than 10 zones.

Each populated zone creates a parent GameObject named BCG_Zone_{markerName}_{seed}. District-component zones store a reference to this parent in lastPopulated; a repopulate replaces the old output automatically.

Populate runs asynchronously — one building per frame — so a large zone does not freeze the editor. A progress bar is shown while the job runs; closing the window aborts it (partial output stays in the scene and can be removed with Undo).

7. Scene tab — inventory & health

The fourth toolbar tab, Scene, is a read-only inventory of every generated building in the open scene — buildings carrying the hidden BCG_BuildingMarker (§16). It does not generate anything; it lets you audit, find, isolate, and clean up what is already placed. If the scene has no generated buildings, the tab shows a hint and a Refresh button.

The inventory is scanned once and cached; it is rebuilt automatically only when the scene hierarchy changes (or when you press the toolbar Refresh button), never on every repaint.

Overview stats

The header summarises the whole scene:

N buildings · X tris · ~N draw calls (pre-batching) — total building count, combined triangle count, and the pre-batching draw-call estimate (one per building before static/SRP batching).
Archetype line — Tower · Shop · Apartment · House counts.
Palette line — the four palette swatches (A – D) with a per-variant building count.

Control	Effect
Search field	Matches a building's GameObject name or its seed.
Archetype filter	All / Tower / Shop / Apartment / House.
Variant filter	All / A / B / C / D.
Refresh	Rescans the open scene.
Flat toggle	Off = grouped by district (default); on = a single flat list.
Sort (Flat only)	Sort the flat list by Tris, Floors, Name, or Footprint.

When any filter is active, a showing X of N line appears above the list.

The list

Grouped view (default) — buildings are grouped under their parent container (BCG_StreetRow_*, BCG_Zone_*, or a (loose) bucket for root-level Single / Variation-Row output, shown last). Each district foldout shows its building count, combined triangles, and a (!) flag if any child has an issue, plus an Isolate button that selects and frames that district in the Scene view.
Row contents — palette swatch + letter, archetype, CellsX×CellsZ F{floors} (or the footprint W×D m when the GameObject was renamed and no longer parses), triangle count, and the seed (or district name in the flat list). A warning icon with a tooltip appears when the building has a health issue. Inactive buildings are dimmed.
Interaction — single-click selects and pings the building; double-click frames it in the Scene view.

Health flags

Each building is checked for the following problems; the row's warning tooltip lists every one that applies:

Flag	Meaning
Missing mesh	No `MeshFilter`, or a null shared mesh.
Missing / magenta material	No renderer, a null material/shader, or Unity's magenta error shader.
Pipeline mismatch	The facade shader does not match the active render pipeline (the pink-under-URP trap). Fix with Fix Materials (§12).
Not marked static	The Batching Static flag is cleared, so the building loses static batching.
Overlapping	The building's gap-padded footprint clips another building's (the same test the placement guard uses — §16).

Bulk actions

The tab's own footer (distinct from the window footer) acts on the list:

N issue(s) / Select flagged — selects every building in the list that has at least one health flag (disabled when there are none).
Select shown — selects every building currently listed (respecting filters).
Isolate — selects the shown buildings and frames them in the Scene view.
Delete shown — after a confirmation dialog, deletes every listed building and any now-empty BCG_StreetRow_* / BCG_Zone_* container. The deletion can be reverted with Undo.

8. BCG_BuildingZone district component

BCG_BuildingZone is a Runtime MonoBehaviour that gives a BoxCollider marker its own per-zone archetype mix, variant allowlist, and layout settings. It requires a BoxCollider on the same GameObject and carries no generation logic, so it is safe in a build.

Serialized fields

District Mix

Field	Type	Default	Description
`towerWeight`	float [0–1]	0.35	Relative chance a plot becomes a Tower.
`shopWeight`	float [0–1]	0.30	Relative chance a plot becomes a Shop.
`apartmentWeight`	float [0–1]	0.35	Relative chance a plot becomes an Apartment.
`houseWeight`	float [0–1]	0.25	Relative chance a plot becomes a gabled House.

Weights are relative (normalized internally); setting all four to 1.0 gives an even mix.

Texture Variants

Field	Type	Default	Description
`variantA`	bool	true	Allow the A – Light Gray palette.
`variantB`	bool	true	Allow the B – Brick palette.
`variantC`	bool	true	Allow the C – Graphite Curtain palette.
`variantD`	bool	true	Allow the D – White Plaster palette.

Layout

Field	Type	Default	Description
`seed`	int	0	0 = auto; the tool writes a stable seed on first populate. Same seed + same bounds → same block.
`edgeMargin`	float [0–8]	1	Distance (m) buildings keep from zone bounds.
`gapMin`	float	4	Minimum random spacing (m) between plots along a row.
`gapMax`	float	10	Maximum random spacing (m) between plots along a row.
`rowGapMin`	float	6	Minimum random alley/street width (m) between rows.
`rowGapMax`	float	10	Maximum random alley/street width (m) between rows.

lastPopulated is hidden in the Inspector and managed by the tool.

Gizmo colors

The component draws an always-visible wire cube over the BoxCollider bounds in local space:

State	Color
Empty (not yet populated)	Cyan — RGB (0.2, 0.9, 1.0)
Populated (`lastPopulated` set)	Green — RGB (0.3, 1.0, 0.4)

When selected, a translucent solid fill (8 % alpha of the same color) is drawn behind the wire cube.

9. Archetype reference

Archetype	Typical height	Massing models	Parapet	Facade styles	Roof
Tower	7–16 floors	Slab / Setback / Podium / L-plan (seeded, tall footprints only)	Concrete parapet	OfficeDark, OfficeLit, Ribbon, Mullion	Flat gravel + roof clutter (HVAC boxes, bulkheads)
Shop	1–2 floors	Slab only	Dark fascia strip	Punched, OfficeDark	Flat gravel
Apartment	3–8 floors	Slab only	Concrete parapet (0.7 m)	Punched, Balcony, OfficeDark	Flat gravel
House	1–2 floors	Slab only	None (parapet fields ignored)	Punched (biased), OfficeDark	Pitched shingle roof (32–40° pitch), eaves, optional chimney

Massing applies only to Tower when floors ≥ 7, cellsX ≥ 6, and cellsZ ≥ 5. All other combinations produce a single Slab regardless of archetype.

Geometric relief (window recession, 0.12 m inset depth): OfficeDark, OfficeLit, and Balcony styles. Ribbon, Mullion, and Punched stay flush.

House pitched roof: pitch is a pure function of seed (32 + |seed| % 9 degrees, range 32–40°). The ridge runs along the longer horizontal axis. A chimney appears with 70 % probability; its position and slope side are seeded.

10. Advanced fields

Expand the Advanced foldout in the main panel.

Field	Range	Default	Notes
Cell Width (m)	2 – 5	3.0	Meters per window cell. Drives both width and depth: `Width = cellsX × cellWidth`.
Floor Height (m)	2.4 – 5	3.2	Height of all floors above the ground floor.
Ground Floor Height (m)	2.8 – 6	4.0	Taller ground floor for storefronts.
Parapet Height (m)	0.2 – 2	0.9	Outer parapet wall height. Ignored for House.
Parapet Thickness (m)	0.15 – 1	0.35	Inward thickness of the parapet cap. Ignored for House.

The archetype presets set sensible defaults (e.g., Shop sets ground floor height to 4.2 m, parapet height to 1.0 m; House sets floor height to 2.8 m, ground floor height to 3.0 m).

11. Regenerate All

The footer Regenerate All button rebuilds every generated prefab in place — mesh and prefab assets are overwritten at their existing paths so GUIDs (and therefore all existing scene references) are preserved.

Use this after upgrading the package to pick up geometry or UV improvements without losing scene placements.

A confirmation dialog is shown before the operation starts. The operation cannot be undone.

12. Fix Materials (Active Pipeline)

The footer Fix Materials button rebuilds all four facade materials (BCG_Building_Facade_A/B/C/D.mat) — plus the demo-ground material — for the currently active render pipeline, overwriting them in place (GUID-stable).

URP active → materials use Universal Render Pipeline/Lit with _BaseMap / _BaseColor / _Smoothness.
Built-in active → materials use Standard with _MainTex / _Glossiness.

Both pipelines set _Smoothness / _Glossiness to 0.12 and enable emission from the matching BCG_Facade_Emission_{A..D}.png atlas. Running Fix Materials also refreshes the footer material-health badge to green (§2).

Night Lights

The Night Lights panel (just above the footer, visible in every mode) sets a single global window-glow look for all buildings. It tints the shared facade materials, so the one-material / one-draw-call-per-building guarantee is preserved. The panel is a collapsible foldout, collapsed by default, whose header shows the current state (Off / Dusk / Night / Custom):

Intensity — emission brightness. 0 turns windows off (day).
Window Color — the glow colour; a warm amber reads as a night skyline.
Day / Dusk / Night presets — one-click looks. The asset ships on the warm Dusk default.

The setting is stored per-user and is honoured by Fix Materials and pipeline switches, so your night look survives a material rebuild. Slider / colour edits mark the four materials dirty (persisted on the next project save); the preset buttons save immediately.

13. Bake UVs (Existing)

The footer Bake UVs (Existing) button adds lightmap UVs and GI contribution to buildings that were already generated — without rebuilding their geometry.

By default, generation skips the per-building lightmap-UV unwrap (the Bake Lightmap UVs toggle below the tab body is off), because city-filler background buildings rarely contribute to a baked GI bake and the unwrap is the single biggest per-building cost. If you later decide some or all of those buildings should be lit by baked GI, use this footer button instead of regenerating everything:

Scope — operates on the current selection. Selecting a BCG_StreetRow_* / BCG_Zone_* parent includes all of its child buildings. If nothing generated is selected, it bakes every generated building in the open scene.
What it does — unwraps a secondary (lightmap) UV set on each unique building mesh that lacks one (done once per shared mesh, not per instance), then turns on the Contribute GI static flag and sets the reduced lightmap scale on every targeted building's renderer — matching exactly what generation does when the toggle is on.

The per-building flag changes can be reverted with Undo. The mesh-asset UV write is an asset modification and cannot be undone (the same as Regenerate All).

14. Save As Prefab Assets

The Save As Prefab Assets toggle (default on) controls whether the four "keep" spawn paths — Single, Variation Row, Street Scatter, and window-driven Populate Zones — write a GUID-stable mesh and prefab asset to Generated/ for each building, or place it in the scene without touching the project on disk.

Setting	Behaviour
On (default)	Each building is saved as a reusable prefab + mesh asset under `Generated/`, then instantiated into the scene. Identical to previous behaviour.
Off	Buildings are placed directly in the scene with no assets written. `Generated/` is not touched. Useful for one-off city-filler geometry where you do not need reusable prefab assets.

When to turn it off — if you are filling a large open-world scene with background geometry that you never need to re-use or re-seed, turning this off keeps Generated/ clean and avoids accumulating hundreds of mesh assets for buildings you will never reference again.

Save-the-scene caveat — scene-only buildings live in the scene file, not in any asset. A domain reload triggered by a script recompile or an editor restart will destroy un-saved scene objects. Save the scene immediately after generating scene-only buildings, or they will be lost.

Note: the Preview In Scene button always builds a no-asset throwaway instance regardless of this toggle — it is an audition view, not a keep path.

This toggle is persisted in EditorPrefs and applies per-user. Changing it has no effect on buildings already in the scene; it only affects the next generation.

15. Pipeline notes

Buildings look pink (magenta) when the facade material references a shader that is not included in the active pipeline. This happens if you:

Import the asset into a URP project without running Fix Materials.
Switch render pipeline after importing.

The footer status badge flags this state (… · materials need Fix, amber dot), and the Scene tab flags each affected building with a Pipeline mismatch warning (§7).

Fix: open Tools > BoneCracker Games > Building Generator > Building Generator and click Fix Materials in the footer. All four material assets are rebuilt for whichever pipeline is currently active; existing prefab references survive the rebuild because the material GUIDs do not change.

Mesh geometry and UV layout are pipeline-agnostic; only the facade materials are pipeline-coupled.

16. Managing generated output

Every building the generator places carries a hidden, data-only BCG_BuildingMarker component — kept out of the Add-Component menu and the Inspector. It records the building's archetype, variant, seed, and footprint, and lets the tool find, select, and clean up generated output. The Scene tab (§7) is the browsable view of everything that carries this marker.

Automatic clip-avoidance

All four placement workflows (Single building, Variation Row, Street Scatter, Populate Zones) avoid overlapping existing generated buildings. Before each building is placed, its footprint is tested against every BCG_BuildingMarker already in the scene; if the intended spot would clip one, the building is moved to the nearest free spot via an outward ring search. A building that fits where intended is left exactly there, so layouts are unchanged in open areas. The console logs how many buildings were relocated.

Only BCG-generated buildings count as obstacles — your own scenery is never moved or avoided.
Clip-avoidance is always on and consumes no random seed, so seeded layouts stay deterministic.

Select All / Destroy All

Two buttons in the window footer act on every generated building in the open scene:

Select All — selects every generated building (the objects carrying a BCG_BuildingMarker) so you can move, inspect, or delete them as a group.
Destroy All — after a confirmation prompt, deletes every generated building and any now-empty BCG_StreetRow_* / BCG_Zone_* container objects. The deletion can be reverted with Undo.

(For finer control — filtering, isolating, or deleting only part of the scene — use the Scene tab's bulk actions, §7.)

Clean Unused Assets

Destroy All removes buildings from the scene; Clean Unused… reclaims the asset files they leave behind on disk. Every building generated with Save As Prefab Assets on writes a mesh (and prefab) under Assets/BCG/BuildingGen/Generated/. Over time, regenerating or deleting buildings can leave mesh/prefab assets that no scene uses any more. The Clean Unused… footer button finds and removes them safely:

Click Clean Unused… in the footer. You'll be prompted to save any unsaved scenes first (so the scan sees the current state).
The tool scans every scene in your project — open and closed — and lists the generated meshes and prefabs that no scene references, with the total disk space you can reclaim.
Review the list (everything is checked by default; use Select None / the per-item checkboxes to keep anything), then click Delete Selected and confirm.

Safe by design: any mesh or prefab used by a building placed in any scene — including the demo scene — is kept. A prefab kept only in your Project window but never placed in a scene is treated as unused; uncheck it in the list if you want to keep it. Deletion is permanent (not undoable), which is why the preview and confirm steps are there. Facade and ground materials are never touched.

17. Package contents

The following folders are shipped with the asset:

Folder	Contents
`Assets/BCG/BuildingGen/Editor/`	Generator window (incl. the Scene inventory tab), mesh builder, zone populator, zone inspector, anti-clipping placement guard, scene-inventory + asset-cleanup cores, onboarding, editor skin
`Assets/BCG/BuildingGen/Runtime/`	`BCG_BuildingZone` (district marker), `BCG_BuildingMarker` (per-building tag), `BCG_BuildingArchetype` (enum), `BuildingGen_Version`
`Assets/BCG/BuildingGen/Textures/`	`BCG_Facade_Albedo_{A,B,C,D}.png` and `BCG_Facade_Emission_{A,B,C,D}.png`
`Assets/BCG/BuildingGen/Demo/`	`BuildingGen_Demo.unity` sample scene
`Assets/BCG/BuildingGen/Documentation/`	This guide and `BuildingGen_AtlasLayout.md`

The following are not shipped:

Assets/BCG/BuildingGen/Generated/ — bulk output (meshes, prefabs, materials); regenerated per project. Only the assets referenced by the demo scene are included.
Assets/BCG/BuildingGen/Tools~/ — internal Python texture-generation scripts.
Assets/BCG/BuildingGen/Editor/Tests/ — Edit Mode tests (development only).
docs/ — design spec and implementation plan (development only).