viewer: nothing passes through a roof

[8Maverik8]

What does this PR do?

Walls, posts and other meshes ignore the roof today: a full-storey wall under a low roof (eaves below the storey height) pokes through the roof and its overhang, and so do posts, furniture or a pipe placed under it. This PR makes a roof cut everything in its building at its underside (the bottom of the deck):

• Walls get one extra CSG subtraction of a heightfield solid above the roof underside (wall-roof-fit.ts), kept separate from the opening union, so the wall top follows the slope with a closed, flat-shaded top. Walls never grow towards a roof.
• Every other mesh of a level — posts, furniture, fences, pipes, ceilings — is clipped geometrically against convex prisms above the underside (roof-clip.ts), whatever its material or loader. The cut face sits against the deck underside and is not visible. Roofs and the nodes they host (chimneys, skylights) are left alone; skinned and instanced meshes are skipped.
• Columns under a roof reach its underside, measured from their slab lift (getFloorStackedPosition), so posts of a terrace or porch meet the roof.

The underside planes come from the same faces the roof renders: the getVol closure in getRoofSegmentBrushes is extracted as getRoofSegmentVolumeFaces, and getRoofSegmentUndersidePolygons returns the deck-bottom faces clipped by the segment trim (roof-underside.ts). Only 3D geometry changes: plans, stored heights, the spatial grid and the roof elevation that follows wall tops keep reading the storey height. A roof edit rebuilds only the walls whose roof cover changed; a mesh is re-clipped only when its geometry, placement or the building's roofs change.

How to test

1. bun test packages/viewer/src/systems/wall/wall-roof-fit.test.ts packages/viewer/src/systems/roof/roof-clip.test.ts — walls cut by a low roof (full-height, partition and half walls), walls outside a roof untouched, roof edit marks only affected walls, posts reach the underside up or down and from a slab, mesh clipping keeps material groups.
2. bun dev, draw a room with full-height walls, add a shed roof whose eave is below the storey height: the walls follow the roof slope instead of poking through.
3. Put a column and an item under the roof: the column reaches the roof underside; anything taller than the underside is cut at it.

Screenshots / screen recording

Before/after screenshots will be added in a comment (tested on a real house plan with a split-level shed roof).

Checklist

• I've tested this locally with bun dev (tested in our fork's editor on a production house plan; on this branch: unit tests and tsc for viewer)
• My code follows the existing code style (run bun check to verify)
• I've updated relevant documentation (if applicable)
• This PR targets the main branch

🤖 Generated with Claude Code

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Note

Medium Risk
Touches core wall CSG and a per-frame mesh clip over the scene graph; incorrect patches or transforms could mis-cut geometry or add frame cost, though invalidation and tests limit blast radius.

Overview
Building content no longer pierces roofs: the viewer derives roof underside patches from the same segment volume data used for roof brushes, then uses them in three paths.

Walls under a roof get an extra CSG subtraction (wall-roof-fit) so the extruded top follows the sloped underside without changing stored storey height; roof edits mark only walls whose cover signature changed.

Other level meshes (furniture, ceilings, etc.) are clipped each frame in runRoofClipFrame against convex regions above those patches; roofs, wall meshes, and skinned/instanced geometry are skipped.

Columns override rendered height via resolveColumnRoofHeight (from slab lift through getFloorStackedPosition) so posts meet the underside; taller geometry can still be trimmed by the mesh clip pass.

getRoofSegmentVolumeFaces / getRoofSegmentUndersidePolygons centralize underside planes; tests cover wall fitting, column height, and clipGeometryByRegions.

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Cursor Bugbot has reviewed your changes using high effort and found 2 potential issues.

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Clipped meshes never restore

High Severity

runRoofClipFrame returns as soon as no building has underside patches, and skips a level when that building’s patch list is empty. Those paths never walk existing meshes, so a deleted or emptied roof leaves furniture, pipes, fences and ceilings permanently cut until remount.

 

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Lower roofs clip storeys above

High Severity

Mesh clipping treats every roof in the building as an unbounded upward prism and, once any patch AABB hits, subtracts all of them. A mesh that sits entirely above a lower roof (room over a porch, split-level wing, garage with a storey above) is removed inside that roof’s outline instead of being left alone. Walls already skip roofs below their base via capPatchAt; this path does not.

Additional Locations (1)

• packages/viewer/src/systems/roof/roof-clip.ts#L43-L68

 

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