houseplan-card/docs/WALL-THICKNESS.md

Wall thickness — the spec

Status: approved, not implemented. Owner's wording (2026-08-05): «в редакторе плана появляется режим "толщина стен". В нем кликаем по стене (стеной считаем грань одной комнаты), там поле ввода толщины в сантиметрах или дюймах (в зависимости от настроек HA). Ввели — стена начинает отображаться с толщиной, внутренность стены заштрихована. Толщина не должна учитываться при расчете площади. Учти изменение отображения проемов в толстых стенах.»

Written against the code as it stands: rooms are polygons, roomEdges() splits them into segments, sharedBoundary() finds where two rooms touch, openings are anchored to a wall by projection (docs/RESIZE.md §, the openingShoulders contract), the paper sheet follows the room contours (docs/BACKDROP.md), and area comes from polygonArea() on the polygon itself.

1. The model: thickness belongs to a WALL, not to a room

A wall is a straight stretch of boundary. Both of the rooms that meet along it see the same physical wall, so one wall carries one thickness, and it can be entered from either side. The alternative — a thickness per room edge — produces two parallel slabs with a hairline gap between them whenever the two numbers differ, and asks the user a question the house does not have an answer to («какая толщина у этой стены со стороны кухни?»).

1.1. Addressing a wall

The hard part. A room's vertex list is not stable: resizing inserts vertices at T-junctions (docs/RESIZE.md), merging and splitting rewrite polygons entirely. So an edge index is out, and so is a pair of endpoint coordinates — dragging the wall moves both.

Thickness is stored per space as a list of entries keyed by a segment key: the midpoint and the direction of the wall, normalised (direction taken modulo 180°, so a wall is the same wall from either end), quantised to the grid pitch. Lookup matches within a tolerance of half a grid step.

Why this survives what indices do not: dragging a wall in the resize tool moves it by whole grid steps, and the entry is rewritten by the same operation that moves the wall — resize already knows which edges it touched, so it re-keys them in the same transaction. Inserting a T-junction vertex splits one edge into two collinear ones; both inherit the parent's thickness, because their midpoints both fall inside the parent's span and the direction is unchanged.

Degradation. If a wall cannot be matched after an edit (a room was redrawn, merged, or cut), the entry is dropped silently on the next write. Rationale: a thickness pointing at a wall that no longer exists is invisible, and keeping it would let a config accumulate ghosts that resurface later when a new wall happens to land on the old key — a surprise worse than losing a number the user can re-enter in two clicks. Never migrate a stale entry onto "the nearest collinear wall": that is a guess about the user's intent, and a wrong guess draws a slab where the user never asked for one.

1.2. Storage

Per space: walls: [{ key, cm }], where key is the quantised segment key and cm the thickness in centimetres (always centimetres in the config, regardless of what the user typed — the unit is a display concern). Absent list, or a wall with no entry, means exactly today's rendering: a line. Optional everywhere, no migration.

Backend: cm bounded to 1…100 (a 1 cm partition and a metre-thick stone wall are both real; outside that range it is a typo), key a bounded string, list length capped like the other per-space collections.

2. Where the thickness goes

• A shared wall grows symmetrically — half into each room. Both rooms lose the same sliver of drawn floor, which is what a real wall does.
• An outer wall grows inward. Outside the house there is nothing to grow into: the plan's outline is where the building ends, and pushing the slab outwards would move the house's silhouette every time someone corrects a number. It also keeps the content frame (docs/CANVAS.md) stable.
• An open boundary (a virtual wall, an open zone) has no thickness and the tool refuses to set one — it is a hole in the wall by definition.

3. Corners

Two thick walls meeting at an angle must join without a gap and without one overlapping the other. The slab is built as an offset of the room contour, not as independent rectangles per edge: each room produces one inner contour (its polygon inset by the local half-thickness of every edge), and the wall body is the ring between the polygon and that inset contour. Corners then resolve as the intersection of the two inset lines — a mitre — which is what a mason builds and what every CAD draws.

Two guards, because mitres blow up on sharp angles:

• when the mitre length exceeds a few times the thickness (a very acute corner), the joint is cut (bevelled) instead — an infinite spike is not a wall;
• when neighbouring edges carry different thicknesses, the inset uses each edge's own offset and the corner is resolved between the two — a step, which is exactly what a thick wall meeting a thin partition looks like.

Verify on: an L-shaped room, an acute corner (30°), a room with one thick and three thin walls, and an island room inside another room.

4. Area, and everything else, stays on the centreline

The user's rule: thickness must not change the area. So the polygon remains the single source of geometric truth. Area, live dimensions during resize, the room card's m², the wall-length rulers, device auto-layout, room fills, the sun's wedges and their clipping, glow spilling through openings — all keep reading the polygon exactly as they do today. Thickness is a rendering layer on top and must not be consulted by any of them.

One deliberate exception: the paper sheet follows the OUTER contour of the thick walls, not the polygon. Otherwise the scene background shows through the body of every wall — the sheet would end at the wall's centreline while the slab is drawn to either side of it. The paper rule from docs/BACKDROP.md ("the sheet is the room contours") is therefore restated as: the sheet is the rooms' contours, grown by whatever thickness their walls carry.

5. Openings in a thick wall

An opening is a hole in the wall, not a mark on its centreline. In a wall with thickness the opening's span is cut out of the slab across its full depth, so the wall body is interrupted and the two rooms see through.

• Window: the slab is interrupted; the glass is drawn as a line across the full depth of the opening, in the middle of the wall body, with the jambs closing the slab on both sides.
• Door: the slab is interrupted the same way; the swing arc starts at the inner face of the wall (the side the door opens into), not at the centreline, because that is where the leaf is hinged.
• The opening's own anchoring is unchanged: it still lives on the wall by projection, and openingShoulders still measures along the centreline. Thickness changes only what is drawn.
• A wall thicker than the opening is long is refused by the same anchor logic that already protects openings during resize.

6. Hatching

The wall body is filled with a diagonal hatch (an SVG pattern), in a colour derived from the room's border colour so it inherits the user's palette and the day/night dimming.

The pattern's pitch is fixed in screen terms, not in plan units: hatching that scales with zoom turns into a solid smear when you zoom out and into stripes a metre wide when you zoom in. Below a threshold — when a wall is only a few pixels wide on screen — the hatch is replaced by a solid fill of the same colour: at that size a pattern is noise, and the reader only needs to see that the wall is a body rather than a line.

7. The tool

A new tool «Толщина стен» in the plan editor, beside Add / Merge / Split / Resize / Opening / Open boundary / Delete. In it:

• hovering highlights the wall under the cursor (the whole wall, both rooms' view of it, so it is obvious that the number applies to both);
• clicking opens a small input anchored next to the wall — one field, in cm or inches by HA's unit system (the same path the furniture library uses), prefilled with the wall's current thickness;
• an empty field or zero removes the thickness and the wall goes back to being a line;
• Esc closes without applying, as everywhere else.

Apply to all walls. Cheap and obviously wanted — a house is usually built of two thicknesses, not twelve. The input gets a secondary action «применить ко всем стенам комнаты»; a plan-wide default is not offered, because outer and inner walls genuinely differ and a single number for the whole space would be wrong more often than right.

8. Hooks and i18n

Per docs/STYLING-HOOKS.md: the wall body carries data-hp="wall", data-id (the segment key) and data-kind (shared | outer). i18n en/ru for the tool, the field, the units and the "apply to all" action.

9. Deliberately not done

• No thickness on decor lines — decor is drawing, not construction.
• No per-side finish (plaster, insulation layers). One body, one hatch.
• No automatic thickness from the backdrop image. Reading wall widths off a photographed plan is image analysis, and a wrong guess is worse than a blank field.
• No effect on the sun's light path. A light shaft is still clipped by the room polygon, not by the wall body: the difference is a few centimetres and the machinery is shared with three other features.

10. Testing notes

Unit (pure): the offset contour (a rectangle inset by half-thickness on every side; one thick edge among thin ones; an L-shape; an acute corner falling back to a bevel), the segment key (same key from either end of the wall; a wall moved by one grid step re-keys; a T-junction split inherits), degradation (a key with no matching wall is dropped), cm↔normalised conversion through cell_cm.

Backend: cm bounds, key length, list cap, and that a space without walls still validates.

Browser (demo/smoke_wall_thickness.mjs): the tool exists and highlights a wall on hover; clicking opens the input; a value draws a hatched body; the room's area is unchanged before and after (read the room card's m²); an opening in a thick wall interrupts the body across its full depth and the door's arc starts at the inner face; a shared wall takes the thickness once and shows it to both rooms; clearing the field restores the line; resizing the room afterwards keeps the thickness on the moved wall; the paper sheet covers the wall body (pixel probe at the middle of a thick wall must not be the scene background).