# Layers And Tile Editing

## What It Does

This subsystem handles normal tile painting, erasing, selection, visible layer management, sparse height layers, and the mapping between visible document edits and stored chunk data.

## Key Files

- `src/worldshaperStudio/interactionController.ts`
- `src/worldshaperStudio/runtime.ts`
- `src/worldshaperStudio/sidebarController.ts`
- `src/worldshaperStudio/mapDocumentController.ts`
- `src/worldshaperStudio/popupSessionStore.ts`
- `src/worldshaperStudio/dom.ts`

## Endpoints It Uses

- primarily saved through `POST /api/world/:worldId/chunks/batch-save`

## Important Data And Rules

- room layer `0` is the base layer
- non-base layers use sparse or transparent-style fill semantics
- height layers are separate structures from room layers
- visibility is tracked in popup session state
- painting in world mode must mark affected chunks dirty

## Invariants And Constraints

- layer ordering matters to rendering and selection behavior
- layer visibility must not destroy layer data
- tile edits in world mode must map local viewport coordinates back to world chunk coordinates
- height layers are not the same thing as standard room layers

## Common Request Themes

- better layer reordering
- more precise tiling tools
- height/elevation features
- snapping or unsnapped placement
- erase or selection behavior

## Triage Questions

- Is this about normal room layers or height layers?
- Does the request affect paint semantics, visibility, ordering, or storage?
- Does it apply to map mode, world mode, or both?