# Hidden Isometric View internals

Issue [#89](https://github.com/Matysh/houseplan-card/issues/89) implements a
hidden, presentation-only volumetric View experiment. The normative contract is
`docs/specs/089-isometric-view-stage1.md`; the fixed rendering decisions are in
`docs/adr/089-isometric-stage1-renderer.md`.

## Activation and lifetime

The feature exists only while the `iso` entry in `src/labs.ts` is live. For the
v1.62 cycle it can be enabled with either `?hp-labs=iso` or
`#hp-labs=iso&space=<id>`. Query operations are applied first and hash operations
second. `-iso` removes this flag and `off` clears every Labs flag. A known URL
operation is persisted in `houseplan_card_labs_v1`; the URL itself is not
rewritten.

The selected presentation is stored per space in `houseplan_card_view_v1`. Flat
is always the initial default. Kiosk has no toggle but reads the saved preference.
Editors and `houseplan-space-card` are always flat.

The current registry entry is live from numeric core `1.62.0` and expires at
`1.65.0`. Thus `1.65.0-beta.1` is already expired. Malformed versions, malformed
entries and duplicate ids fail closed. Labs never gate schemas, migrations,
stores, service calls or network requests.

## Coordinate systems

- Plan points are the existing 1000-unit logical floor coordinates.
- Scene points are coordinates in the effective SVG viewBox.
- HTML devices, vacuum pucks, room labels/cards and lock markers stay
  screen-facing. Their anchors use the same `projectPlanPoint()` snapshot as the
  SVG floor.
- `clientToScenePoint()` maps a client point to the current scene; floor hit
  testing then uses `unprojectFloorPoint()`.

Stage 1 uses a fixed orthographic affine camera:

```text
rotDeg=0, tiltDeg=20, xyScale=1, zScale=1, origin=[500,500]
wallHeight=64 plan units
```

There is no perspective, free rotation or user tilt. Switching projections
preserves scalar zoom and converts the view centre through logical floor space.
`projectedFrame()` includes both floor corners and wall-top corners so fit/home
cannot clip the volume.

## Geometry and composition

`src/iso-projection.ts` owns pure projection math. `src/iso-walls.ts` consumes
the canonical `wallBodiesGeometry()` MultiPolygon after openings and extra
physical bodies have been resolved. It normalizes outer/hole winding, builds one
evenodd top path and at most one visible side per ring edge, then uses a stable
depth/order tie-break. Complexity is O(E) in canonical ring edges.

For connected drafts and partitions those extras already contain computed
bounded junction patches. Isometric wall tops/sides therefore use the same
seamless L/T footprint as flat full/static cards; raw per-record rectangles are
reserved for editor identity and never projected as competing wall faces.

The content fingerprint includes rooms, wall geometry/thickness, open cuts,
openings, partitions, drafts, columns, scale/grid inputs, camera, wall height and
algorithm version. It deliberately excludes `_cfgEpoch`, HA state, hover and
`show_borders`. The per-card LRU is capped at eight scenes. Pan, zoom and HA-only
updates reuse it.

Composition remains SVG-first:

1. the existing floor SVG and all its current live layers;
2. explicit visible wall sides and wall top;
3. screen-facing HTML overlays.

The floor keeps the same nodes and order for paper/backdrop, room fills/hover,
Glow/spill, sun, decor/furniture, opening symbols and vacuum path/outline. Stage
1 does not add a second light source/layer. Markers and room cards intentionally
remain above walls without geometric occlusion.

## Failure boundary

Projection/topology failures latch flat fallback for the current
`space|fingerprint`. One diagnostic is emitted without config, entity ids or URL
data. The saved iso preference is retained; an explicit iso request retries the
fingerprint, and changed geometry receives a new fingerprint. Flat rendering is
the rollback path and does not depend on the iso cache.

## Deliberate Stage 1 limits

- door, window and gate keep their current floor-plane symbol and live state;
- no vertical leaf/window panels, sill model or new window light;
- no floor-edge extrusion, shadows, photorealistic materials or marker
  occlusion;
- no volumetric editor and no volumetric `houseplan-space-card`;
- no YAML/config option or public settings surface.

Golden references are accepted only from the complete reviewed Linux artifact.
The full `large-house-isometric-v1` performance comparison is also canonical on
the exact Linux CI SHA.

## Stage 2 composition (#122)

Stage 2 evolves the same hidden `iso` experiment; it does not add a flag,
setting or public activation path. The accepted implementation contract is
`docs/specs/122-isometric-stage2.md` and the fixed composition decisions are in
`docs/adr/122-isometric-stage2-composition.md`. The Labs `since: 1.62.0` and
exclusive `expires: 1.65.0` boundary are unchanged.

### One structural scene, live opening leaves

The per-card LRU remains capped at eight entries. Its Stage 2 value contains:

- canonical wall top/sides and the physical-wall contact path;
- a room/exterior floor footprint and its low visible outer faces;
- immutable opening jamb/axis bases, including type, flips and selected wall
  face;
- the shared projected frame, including wall/opening tops and the low floor
  edge.

The key includes rooms, masonry/opening geometry, flips, scale/camera, wall and
edge heights and algorithm revision. It excludes HA state, theme, hover,
day/night and filter capability. `openingAmount()` is applied only after an LRU
hit by `projectIsoOpening()`, so a contact update projects O(O) leaves without
repeating a wall or floor boolean operation.

`floorFootprintGeometry()` deliberately accepts no independent physical-body
input. The slab is the union of room floors and derived exterior masonry:
internal room boundaries and nested holes make no decorative step, detached
room components keep separate outside edges, while partitions and columns do
not enlarge it.

### Layer order and materials

All geometry roots use one scene `viewBox`. The existing floor/live nodes are
grouped under the Stage 1 affine matrix; HTML anchors still use
`projectPlanPoint()`.

```text
stage background
→ shared ambient shadow + low exterior floor edge
→ existing floor SVG (paper/image, room fills/hover, decor, Glow, sun)
→ shared contact and live leaf shadows
→ canonical wall sides/top + inert vertical opening panels
→ existing HTML devices, labels/cards, locks and vacuum overlays
```

Wall top and side use two shared matte gradients. Ambient, contact and leaf
shadows use three shared filters; definition count is constant per card, never
per face or opening. Forced colours use solid `Canvas`/`CanvasText` faces and
omit decoration. A runtime without the required filter paint keeps solid
structure, floor edge and vertical panels but emits no Stage 2 shadows; this
does not enter the structural fallback latch.

### Vertical openings and display settings

`src/iso-openings.ts` mirrors the existing opening-symbol transform algebra:
door has one jamb-hinged leaf, gate has two leaves with the established
0–10° exterior-face turn, and window has two light neutral casements. A saved
`passage` keeps the same full-height masonry cut but has zero leaves/panels and
therefore no panel or leaf shadow. Heights are fixed presentation ratios of
`ISO_WALL_HEIGHT`; there is no schema field.
The panel basis consumes the same pure visible-offset contract as Flat: default
door/window/gate panels are always centred across wall depth. `flip_v` changes
only door/window direction or the gate turn and never translates the structural
origin. Jamb/cut depth remains physical and independent of symbol placement.
Panels/shadows are pointer- and ARIA-inert. Existing lock badges/cards and HA
actions remain the only interactive opening surface.

- borders visible: vertical panels replace the floor-plane symbols;
- `hide_openings: true`: panels and leaf shadows disappear, while masonry
  cuts, Glow/sun and contact/lock meaning remain;
- `show_borders: false`: Stage 2 roots are absent and the established floor
  symbols and Stage 1 projected frame return (subject to `hide_openings`),
  avoiding floating panels or an invisible Stage 2 bound that reframes them;
- Flat, editors and `houseplan-space-card` retain their old symbols and DOM.

Stage 2 adds no window beam, Glow source, sun renderer, material config,
network request or HA service path. Structural topology/projection exceptions
still use the Stage 1 latched Flat fallback. The known independent exact-SHA
view-toggle performance debt remains tracked in #124; #122 neither weakens its
budget nor treats fallback as benchmark success.