bonsai-walls

name	bonsai-walls
description	Create rooms and polyline walls (with PROPER MITERED CORNERS) and fitted floor slabs in Blender + Bonsai. Matches what bpy.ops.bim.draw_polyline_wall and bpy.ops.bim.draw_slab_from_wall produce interactively. Trigger when the user wants to programmatically build IFC walls / partitions / a room outline / a slab fitted to wall geometry.

bonsai-walls — walls + slabs + mitered corners

When to use this

Trigger on:

• "build a room", "create a room", "polyline walls"
• "interior wall", "partition", "divider"
• "exterior wall", "load-bearing wall"
• "floor slab", "fit slab to walls"

For openings + doors + windows: see bonsai-openings. For roofs and roof-to-wall fits: see bonsai-roofs. For stairs + railings: see bonsai-stairs. For spaces + grid: see bonsai-spaces-grid. For project setup + audit + IDS: see bonsai-project-setup.

Core principle: ALWAYS IFC/BIM-correct

Every element, void, fill, material, parametric attribute MUST be a real IFC entity with proper relationships. Blender modifiers (Boolean, Solidify, Array) and direct mesh edits LOOK right in the viewport but get LOST on IFC export and break interop with every other IFC tool (Solibri, BIMVision, IFC.js, Revit, ArchiCAD).

For every operation, ask: "Will this survive bim.save_project → close → re-open?" If no, find the IFC mechanism. The common ones:

Intent	✅ IFC-correct mechanism	❌ Don't
Wall body	DumbWallGenerator.create_wall_from_2_points → LAYER2 + material set	Plain mesh bpy.ops.mesh.primitive_cube_add
Wall-to-wall connection	DumbWallJoiner.connect → IfcRelConnectsPathElements + miter regen	Just place walls touching each other
Wall clip / cut	ifcopenshell.api.geometry.add_clipping → IfcBooleanClippingResult	Blender Boolean modifier
Slab from walls	DumbSlabGenerator("WALLS") + Z-translate via edit_object_placement	bpy.ops.mesh.primitive_plane_add
Material	material.assign_material → IfcRelAssociatesMaterial + constituent set	Blender material slot only

Why the obvious approaches fail

Approach	Problem
ifc-bonsai-mcp create_polyline_walls	Creates independent walls; no IFC connections; corners overlap
bpy.ops.bim.extend_walls_to_wall	Requires LAYER2-compatible walls; produces butt-joints (one wall ends at the other's face), not the wall-axis miter
bpy.ops.bim.add_occurrence per segment	Creates 1m-default walls; doesn't set proper axis representation length
bpy.ops.bim.draw_polyline_wall	Modal/interactive operator — can't be driven from a script

What actually works

From the Bonsai source (<your_local_clone>/IfcOpenShell/src/bonsai/bonsai/bim/module/model/wall.py):

1. DumbWallGenerator(relating_type) — builds typed LAYER2 walls via create_wall_from_2_points() with correct length / rotation / axis representation and material layer thickness.
2. DumbWallJoiner().connect(wall_a, wall_b) for each consecutive pair — calls ifcopenshell.api.geometry.connect_wall() which creates IfcRelConnectsPathElements with ATSTART/ATEND, then tool.Model.recreate_wall() regenerates the body with miter (algorithm in regenerate_wall_representation.py:525).

How to use

Inside Blender (Scripting workspace, or via execute_blender_code MCP):

import bonsai_bim_helpers as bw

# 5 × 5 m room with WAL100 walls, 3 m high, FLR200 slab
pairs = bw.create_room_with_mitered_corners(
    corners=[(0, 0), (5, 0), (5, 5), (0, 5)],
    wall_type_name="WAL100",
    height=3.0,
    closed=True,
    name_prefix="Room",
)
walls = [obj for obj, _ in pairs]

slab_obj, slab_entity = bw.add_floor_slab_from_walls(
    wall_objs=walls,
    slab_type_name="FLR200",
    align_top_to_storey=True,    # slab top at Z=0, walls sit on top
)

Why align_top_to_storey=True matters

By default DumbSlabGenerator extrudes the slab UPWARD from the storey reference plane (Z=0), so the slab body occupies Z=0 … +thickness and overlaps the bottom of the walls. With align_top_to_storey=True, the slab placement is translated DOWN by its thickness via ifcopenshell.api.geometry.edit_object_placement, so the slab top sits at Z=0 and walls rest cleanly on top.

Prerequisites in the IFC project

• An IFC project must exist (use setup_project() from bonsai-project-setup for a one-shot setup).
• At least one IfcWallType with a material layer set so tool.Model.get_material_layer_parameters(wall_type)["thickness"] returns a value. setup_project() ships WAL200 (200 mm exterior) and WAL100 (100 mm interior) by default.

Wall types convention — exterior vs interior

setup_project(...) creates TWO IfcWallType entries by default:

• WAL200 — 200 mm thick. Exterior + structural use.
• WAL100 — 100 mm thick. Interior partitions.

Both reference one shared IfcMaterial "Concrete" via separate IfcMaterialLayerSet entries (different layer thicknesses per type).

Helper	Default wall type
create_room_with_mitered_corners(..., wall_type_name=None)	First IfcWallType in the project = WAL200
create_room_with_mitered_corners(..., wall_type_name="WAL100")	Explicit interior
add_interior_wall(..., wall_type_name="WAL100")	Default WAL100 (interior)

Both helpers fall back gracefully to the FIRST IfcWallType in the project if the named one is missing.

Interior partitions MUST NOT overshoot into exterior walls

Default rule — when an interior partition (e.g. WAL100) terminates at an exterior wall (e.g. WAL200), its AXIS endpoint MUST sit at the INNER FACE of the exterior wall, NOT at the outer face or centreline. Otherwise the partition body extends into the exterior wall — a knife-through-wall design error that:

• Breaks IFC element separation
• Shows up as an extruded sliver in every section view
• Renders incorrectly in Solibri / BIMVision / IFC.js
• Confuses quantity takeoffs (the partition's volume includes the overshoot)

add_interior_wall(...) auto-clips endpoints by default (avoid_existing_walls=True):

# Pass raw outer-edge coords — helper clips silently to (0.2, 6) → (4.625, 6)
bw.add_interior_wall(
    start_xy=(0.0, 6.0),     # would be inside the 200 mm west wall
    end_xy=(4.625, 6.0),
    height=3.0,
    wall_type_name="WAL100",
    name="Int_NW_South",
)

The clip rule:

1. For each endpoint, find every existing IfcWall whose thickness is STRICTLY GREATER than the new partition's thickness.
2. If the endpoint sits inside (or on the boundary of) that wall's XY bounding box, push it along the partition direction (toward the OTHER endpoint) until just past the bbox boundary.
3. Same-thickness sibling partitions are SKIPPED (so L-corners between two partitions stay intact).

Override with avoid_existing_walls=False ONLY for genuine through-walls or non-axis-aligned obstacle geometry.

Interior L-corners get IfcRelConnectsPathElements — siblings only

Companion rule — when two interior partitions of the SAME thickness meet at an L-corner, they get a proper IfcRelConnectsPathElements + mitered geometry. Partitions meeting EXTERIOR walls (different thickness) do NOT get this connection — they stay as clean butt joints from the no-overshoot clip.

Why the asymmetry — Bonsai's connect_wall (at <your_local_clone>/IfcOpenShell/src/ifcopenshell-python/ifcopenshell/api/geometry/connect_wall.py) writes connection types by picking the NEAREST endpoint of each wall. For two sibling partitions both ENDING at a corner this is correct (ATEND/ATEND → miter). For a partition meeting an exterior wall in a T-junction, the exterior wall does NOT end at the junction — but connect_wall still picks its nearest endpoint and the subsequent recreate_wall TRIMS the exterior wall to that endpoint.

Observed catastrophically on the 10×20 office: 20 m north wall trimmed to 10.85 m fragment between two partition T-junctions; east + west walls reduced from 10 m to 6.1 m.

Until we wire connect_wall's is_atpath=True branch explicitly, the safe rule is same-thickness siblings only:

add_interior_wall(...) does this automatically via connect_to_touching= True (default). After the no-overshoot clip:

1. Compute the new partition's own thickness from its IfcWallType.
2. Read both axis endpoints in world coords.
3. Find every existing IfcWall whose XY bbox contains either endpoint (within 10 mm) AND whose thickness matches the new partition's within 1 mm.
4. Call DumbWallJoiner().connect(new, sibling) for each match.

Partition-to-exterior junctions are intentionally left disconnected — the geometry is right (axis ends at exterior inner face), only the IFC topology is missing. Downstream tools handle this gracefully via spatial adjacency.

Set connect_to_touching=False to disable when you'll wire all connections yourself.

Gotchas

• The Bonsai socket addon defaults to port 9876 (or 9877 if taken).
• BIMModelProperties.relating_type_id is a restricted EnumProperty — don't write to it. Pass the type ID directly to add_occurrence, or use the generator's relating_type constructor arg.
• Blender object name and IFC entity name are SEPARATE — set both if you want them to match.
• The miter is geometrically correct for any angle ≠ 0° and ≠ 180°. For perpendicular walls (90°) the miter cut is exactly 45°.
• Re-running on a populated scene leaves orphan walls at the same XYZ positions, which COVER UP doors/windows so they look "stuck on" or "fragmented". Use cleanup_orphan_walls(name_prefix_to_keep) before adding fillings. The voids are still correct — they're just hidden by the duplicate uncut wall.

Authoritative source references

File	Lines	What
bim/module/model/wall.py	(whole)	DumbWallGenerator, DumbWallJoiner
ifcopenshell/api/geometry/connect_wall.py	30-64	ATSTART/ATEND/ATPATH assignment
ifcopenshell/api/geometry/regenerate_wall_representation.py	525+	Miter geometry computation

Cloneable from github.com/IfcOpenShell/IfcOpenShell.