diff --git a/README.md b/README.md
index f775f298..416a64e7 100644
--- a/README.md
+++ b/README.md
@@ -38,7 +38,7 @@ npm run build        # writes dist/ and regenerates index.html; the folder is wh
 The browser suite and the three example games need a machine with a GPU:
 
 ```bash
-node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1027 checks (GM_STEPS=20 for one step)
+node tools/seed-e2e.mjs && node tools/e2e.mjs      # the editor, 1032 checks (GM_STEPS=20 for one step)
 node tools/seed-jumprun.mjs && node tools/smoke-jumprun.mjs
 node tools/seed-tetris.mjs && node tools/smoke-tetris.mjs
 node tools/seed-actor.mjs && node tools/smoke-actor.mjs
diff --git a/src/editor/Editor.ts b/src/editor/Editor.ts
index 2562be48..7bd9bba3 100644
--- a/src/editor/Editor.ts
+++ b/src/editor/Editor.ts
@@ -33,6 +33,7 @@ import { AnimationEditor } from './animation/AnimationEditor';
 import { TileEditor } from './tile/TileEditor';
 import { AssetPanel } from './panels/AssetPanel';
 import { HierarchyPanel } from './panels/HierarchyPanel';
+import { TilemapPanel } from './panels/TilemapPanel';
 import { Toolbar } from './panels/Toolbar';
 import { type PlayHost, PlaySession, type WorldSnapshot } from './PlaySession';
 import { ProjectSession } from './ProjectSession';
@@ -142,6 +143,11 @@ export class Editor implements PlayHost {
   readonly hierarchy: HierarchyPanel;
   readonly assets: AssetPanel;
   readonly inspector: Inspector;
+  /** Beside the scene view, while exactly one placed tilemap is selected there (#142). */
+  readonly tilemapPanel: TilemapPanel;
+  readonly tilemapSplitter = new Splitter('x');
+  /** The scene tab: its view, and the tilemap panel to its right when there is one. */
+  private readonly sceneRow = new HStack();
   readonly console = new ConsolePanel();
   tab: TabId = 'scene';
   /** Frame rate, refreshed twice a second; null until the first measurement. */
@@ -168,6 +174,8 @@ export class Editor implements PlayHost {
   private fpsElapsed = 0;
   private leftWidth = 250;
   private rightWidth = 350;
+  /** Starts out as wide as the inspector, then goes its own way. */
+  private tilemapWidth = this.rightWidth;
   private consoleHeight = 300;
   /** The asset panel's part of the left column's height; the scene objects get the rest. */
   private assetsShare = 0.5;
@@ -194,6 +202,7 @@ export class Editor implements PlayHost {
     this.listEditor = new ListEditor(state);
     this.hierarchy = new HierarchyPanel(state);
     this.inspector = new Inspector(state);
+    this.tilemapPanel = new TilemapPanel(state);
     this.play = new PlaySession(state, this);
     this.editorRun = new EditorRun(state, {
       // The game view is the one place where no key means anything to the editor, so that is where
@@ -250,8 +259,19 @@ export class Editor implements PlayHost {
     this.tabs.minHeight = Theme.controlHeight + 8;
     // Written out per tab rather than derived, because a `Record<CentreTab, …>` is what makes
     // adding a tab a type error everywhere it has to be handled instead of a silent omission.
+    this.sceneRow.add(this.viewport, 1);
+    this.sceneRow.add(this.tilemapSplitter);
+    this.sceneRow.add(this.tilemapPanel);
+    this.tilemapPanel.minWidth = this.tilemapWidth;
+    this.tilemapSplitter.onDrag = (delta) => {
+      this.tilemapWidth = clamp(this.tilemapWidth - delta, MIN_RIGHT_WIDTH, MAX_RIGHT_WIDTH);
+      this.tilemapPanel.minWidth = this.tilemapWidth;
+      this.sceneRow.relayout();
+    };
+    this.tilemapPanel.onTargetChange = () => this.syncTilemapPanel();
+    this.syncTilemapPanel();
     this.panes = {
-      scene: this.viewport,
+      scene: this.sceneRow,
       game: this.gameView,
       graph: this.graphEditor,
       statemachine: this.stateMachineEditor,
@@ -397,11 +417,23 @@ export class Editor implements PlayHost {
     );
     for (const key of TAB_ORDER) this.panes[key].visible = key === tab;
     for (const [key, pane] of this.pluginPanes) pane.visible = key === tab;
+    // The view checks its own flag before it redraws, and the row around it is what switches now.
+    this.viewport.visible = tab === 'scene';
+    this.syncTilemapPanel();
     this.tabs.setActive(tab);
     this.centre.relayout();
     ui().focus.validate();
   }
 
+  /** The tilemap panel belongs to the scene tab and needs a map to paint; otherwise the view gets its room. */
+  private syncTilemapPanel(): void {
+    const shown = this.tab === 'scene' && this.tilemapPanel.hasTarget;
+    if (this.tilemapPanel.visible === shown) return;
+    this.tilemapPanel.visible = shown;
+    this.tilemapSplitter.visible = shown;
+    this.sceneRow.relayout();
+  }
+
   /**
    * Global x-extent of the tab buttons in the row, from the widget box – not `getBounds()`, which
    * on an untoggled ghost tab sees nothing but the label (the background is not drawn at all).
diff --git a/src/editor/debugHook.ts b/src/editor/debugHook.ts
index 4f45bee4..c8bc9375 100644
--- a/src/editor/debugHook.ts
+++ b/src/editor/debugHook.ts
@@ -29,7 +29,7 @@ import { currentFontPicker } from './font/FontPicker';
 import { currentNodePalette } from './graph/NodePalette';
 import { currentSoundPicker } from './sound/SoundPicker';
 import { currentImagePicker } from './texture/ImagePicker';
-import { currentTilemapSection } from './inspector/tilemapSection';
+import { currentTilemapSection } from './panels/TilemapPanel';
 import type { EditorState, TilemapTool } from './state';
 
 /**
@@ -554,7 +554,22 @@ export function installDebugHook(app: Application, state: EditorState, editor: E
       gameInfo: (objectId: string) => gameView.tilemapInfo(objectId),
       /** Where the scene view outlines the map as blocking: the merged rectangles, in cells (#132). */
       solids: (objectId: string) => viewport.solidInfo(objectId),
-      /** Where the widgets of the inspector section sit: their texts are on screen elsewhere too. */
+      /**
+       * The painting panel beside the scene view (#142): whether it is on screen, its box, the
+       * scene view's box next to it and its splitter – null boxes while it is hidden.
+       */
+      panel: () => {
+        // The editor hides the panel itself on every other tab, so its own flag is the whole answer.
+        const shown = editor.tilemapPanel.visible;
+        return {
+          shown,
+          title: editor.tilemapPanel.title,
+          panel: shown ? rectOf(editor.tilemapPanel) : null,
+          splitter: shown ? centreOf(editor.tilemapSplitter) : null,
+          viewport: rectOf(viewport),
+        };
+      },
+      /** Where the widgets of the painting panel sit: their texts are on screen elsewhere too. */
       toolAt: (tool: string) => {
         const button = currentTilemapSection()?.tools.get(tool as TilemapTool);
         return button ? centreOf(button) : null;
diff --git a/src/editor/inspector/objectSection.ts b/src/editor/inspector/objectSection.ts
index d4812f73..159a211b 100644
--- a/src/editor/inspector/objectSection.ts
+++ b/src/editor/inspector/objectSection.ts
@@ -47,7 +47,6 @@ import { addGap, addNameField, addNote, addTitle, type InspectorHost } from './h
 import type { EditorState, ListSlot } from '../state';
 import { parentRow } from './parentRow';
 import { listOpener, previewingHandlers, structFields } from './previewHandlers';
-import { buildTilemapSection, tilemapSignature } from './tilemapSection';
 import { overrideValue } from './valueSpecs';
 import { buildVariable } from './variableRows';
 import { currentProps, currentRef, deviations, positionMoved, targetOf, viewOf } from './objectQueries';
@@ -83,8 +82,7 @@ export function objectSignature(
       ? 'instance'
       : '';
   const rows = schemaForObject(project, asset, object);
-  const painting = asset.type === 'tilemap' ? `|${tilemapSignature(state, asset)}` : '';
-  return `${object.parentId}|${kind}|` + rows.map(defSignature).join(',') + painting;
+  return `${object.parentId}|${kind}|` + rows.map(defSignature).join(',');
 }
 
 /** Several objects: what they are, and the actions that apply to all of them at once. */
@@ -207,7 +205,6 @@ export function buildObjectSection(host: InspectorHost, holderId: string, object
   markObjectRows(host, object, asset, target);
 
   if (asset.type === 'container') contentSection(host, holderId, object, asset.objects.length);
-  if (asset.type === 'tilemap') buildTilemapSection(host, asset);
 }
 
 function assetLink(host: InspectorHost, label: string, asset: Asset): void {
diff --git a/src/editor/inspector/tilemapSection.ts b/src/editor/panels/TilemapPanel.ts
similarity index 61%
rename from src/editor/inspector/tilemapSection.ts
rename to src/editor/panels/TilemapPanel.ts
index 8303a8a0..6e28959d 100644
--- a/src/editor/inspector/tilemapSection.ts
+++ b/src/editor/panels/TilemapPanel.ts
@@ -1,7 +1,8 @@
 /**
  * The painting side of a placed tilemap (#128): which layer is painted on, with which tile and
- * with which tool. It hangs below the ordinary rows of the object, the way a container's content
- * section does – the grid size and the cell size are plain properties and are shown above.
+ * with which tool. It is a panel of its own beside the scene view (#142), shown only while exactly
+ * one placed tilemap is selected there – the grid size and the cell size are plain properties and
+ * stay in the inspector.
  *
  * Nothing here belongs to the model except the layers themselves: tool, tile and layer are
  * editor state (`state.tilemapPaint`), so opening a project does not decide what one paints with.
@@ -14,12 +15,27 @@ import {
   SetTilemapLayerHiddenCommand,
 } from '../../core/commands/tilemapCommands';
 import type { TilemapAsset } from '../../core/model/Asset';
+import { findObject } from '../../core/model/hierarchy';
+import { resolvedHolder } from '../../core/model/instance';
+import { findAssetOf } from '../../core/model/Project';
 import { findLayer, isLayerVisible } from '../../core/model/tilemap';
-import { Button, Checkbox, Dropdown, HStack, Menu, TextField, Theme } from '../../ui';
+import {
+  Button,
+  Checkbox,
+  Dropdown,
+  HStack,
+  Menu,
+  Panel,
+  ScrollContainer,
+  TextField,
+  Theme,
+  ui,
+  VStack,
+} from '../../ui';
 import type { EditorState, TilemapFocus, TilemapTool } from '../state';
 import { TilePalette } from '../tile/TilePalette';
-import { labelledRow } from './fieldFactory';
-import { addGap, addNote, addTitle, type InspectorHost } from './host';
+import { labelledRow } from '../inspector/fieldFactory';
+import { addGap, addNote, addTitle, type InspectorHost } from '../inspector/host';
 
 const FOCUS: { focus: TilemapFocus; label: string }[] = [
   { focus: 'all', label: 'All layers' },
@@ -35,7 +51,21 @@ const TOOLS: { tool: TilemapTool; label: string; hint: string }[] = [
 ];
 
 /**
- * The layer that is painted on. The one chosen in the inspector when it still exists, otherwise
+ * The tilemap that is painted on: the one scene object selected, placed in the active scene. A
+ * second object in the selection means there is no single map to paint, so there is none (#142).
+ */
+export function paintedTilemap(state: EditorState): { objectId: string; asset: TilemapAsset } | null {
+  const s = state.selection;
+  const scene = state.activeScene;
+  if (s?.kind !== 'object' || s.objectIds.length !== 1 || !scene) return null;
+  // Looked up in the scene as shown, so an object of another scene or a container is not found.
+  const object = findObject(resolvedHolder(state.project, scene), s.objectId);
+  const asset = object && findAssetOf(state.project, object.assetId, 'tilemap');
+  return asset ? { objectId: s.objectId, asset } : null;
+}
+
+/**
+ * The layer that is painted on. The one chosen in the panel when it still exists, otherwise
  * the topmost – so a fresh selection can be painted on without choosing anything first.
  */
 export function paintedLayerId(state: EditorState, asset: TilemapAsset): string {
@@ -63,11 +93,89 @@ export interface TilemapSectionWidgets {
 
 let built: TilemapSectionWidgets | null = null;
 
+/** Null while the panel has no tilemap to paint, so a check cannot click a widget that is gone. */
 export function currentTilemapSection(): TilemapSectionWidgets | null {
   return built;
 }
 
-export function buildTilemapSection(host: InspectorHost, asset: TilemapAsset): void {
+/**
+ * The panel itself. Whether it is on screen is the editor's call – it also depends on the tab –
+ * and `onTargetChange` tells it when the answer may have changed.
+ */
+export class TilemapPanel extends Panel {
+  private readonly scroll = new ScrollContainer();
+  private host: InspectorHost;
+  /** Describes what the rows were built for; a change means a rebuild. */
+  private signature = '';
+  /** A rebuild that was due while the name field had focus – the same rule as the inspector's. */
+  private rebuildWhenLeft = false;
+  /** As set, before the header upper-cases it – for the check scripts. */
+  title = 'Tilemap';
+  onTargetChange: () => void = () => {};
+
+  constructor(private readonly state: EditorState) {
+    super({ title: 'Tilemap', padding: 0, gap: 0 });
+    this.host = this.emptyHost();
+    this.scroll.setContent(this.host.body);
+    this.content.add(this.scroll, 1);
+    state.on('selection', () => this.sync());
+    state.on('load', () => this.sync());
+    state.on('project', () => {
+      if (this.currentSignature() === this.signature) return;
+      if (ui().focus.isWithin(this)) this.rebuildWhenLeft = true;
+      else this.sync();
+    });
+    ui().focus.changeHandlers.push(() => {
+      if (this.rebuildWhenLeft && !ui().focus.isWithin(this)) this.sync();
+    });
+    this.sync();
+  }
+
+  /** Whether there is a map to paint – the editor adds "and the scene tab is showing". */
+  get hasTarget(): boolean {
+    return built !== null;
+  }
+
+  private emptyHost(): InspectorHost {
+    return {
+      state: this.state,
+      project: () => this.state.project,
+      liveVariables: () => null,
+      body: new VStack({ padding: Theme.padding, gap: Theme.gap }),
+      fields: new Map(),
+      nameField: null,
+    };
+  }
+
+  private currentSignature(): string {
+    const target = paintedTilemap(this.state);
+    if (!target) return '';
+    const { objectId, asset } = target;
+    return `${objectId}|${asset.id}|${asset.name}|${tilemapSignature(this.state, asset)}`;
+  }
+
+  private sync(): void {
+    const target = paintedTilemap(this.state);
+    // With the panel gone nothing shows the brush any more, and a click on the next map would paint.
+    // The tile and the layer stay as they were: they are what one comes back to.
+    if (!target && this.state.tilemapPaint.tool !== 'select') {
+      this.state.setTilemapPaint({ tool: 'select' });
+      return;
+    }
+    this.rebuildWhenLeft = false;
+    this.signature = this.currentSignature();
+    this.host.body.destroy({ children: true });
+    this.host = this.emptyHost();
+    built = null;
+    this.title = target ? `Tilemap · ${target.asset.name}` : 'Tilemap';
+    this.setTitle(this.title);
+    if (target) buildTilemapSection(this.host, target.asset);
+    this.scroll.setContent(this.host.body);
+    this.onTargetChange();
+  }
+}
+
+function buildTilemapSection(host: InspectorHost, asset: TilemapAsset): void {
   const { state } = host;
   const paint = state.tilemapPaint;
   const painted = paintedLayerId(state, asset);
@@ -184,12 +292,12 @@ function tileIdsOf(state: EditorState): string[] {
 }
 
 /**
- * What the section is built from, for the inspector's rebuild check: the layers, the tiles on offer
+ * What the section is built from, for the panel's rebuild check: the layers, the tiles on offer
  * and what is painted with. The cells themselves are deliberately absent – a stroke must not
  * rebuild the panel under the pointer that is drawing it – and so are the tiles' pictures and
  * names, which the palette repaints by itself.
  */
-export function tilemapSignature(state: EditorState, asset: TilemapAsset): string {
+function tilemapSignature(state: EditorState, asset: TilemapAsset): string {
   const paint = state.tilemapPaint;
   const layers = asset.layers.map((l) => `${l.id}:${l.name}:${isLayerVisible(l) ? 1 : 0}`).join(',');
   const tiles = tileIdsOf(state).join(',');
diff --git a/src/editor/viewport/FreeViewport.ts b/src/editor/viewport/FreeViewport.ts
index 73f47eaf..1d1a2f99 100644
--- a/src/editor/viewport/FreeViewport.ts
+++ b/src/editor/viewport/FreeViewport.ts
@@ -19,6 +19,8 @@ export abstract class FreeViewport extends WorldViewport {
   /** World point at the viewport centre, and zoom. */
   protected view = { x: 0, y: 0, zoom: 1 };
   private panning: { startX: number; startY: number; viewX: number; viewY: number } | null = null;
+  /** Global position of the top-left corner at the last resize, for `resize()` to keep the world in place. */
+  private screenOrigin = { x: 0, y: 0 };
 
   protected constructor(state: EditorState) {
     super(state);
@@ -57,6 +59,22 @@ export abstract class FreeViewport extends WorldViewport {
     this.redraw();
   }
 
+  /**
+   * Keeps the world where it is on screen when the view's edges move – a panel appearing beside it,
+   * a splitter, the console – instead of holding the centre, which shifted the content by half the
+   * change. The parent positions before it resizes, so the global origin is already the new one.
+   */
+  override resize(w: number, h: number): void {
+    if (this.w > 0 && this.h > 0 && (w !== this.w || h !== this.h)) {
+      const before = this.screenOrigin;
+      const after = this.getGlobalPosition();
+      this.view.x += (after.x + w / 2 - (before.x + this.w / 2)) / this.view.zoom;
+      this.view.y += (after.y + h / 2 - (before.y + this.h / 2)) / this.view.zoom;
+    }
+    super.resize(w, h);
+    this.screenOrigin = this.getGlobalPosition();
+  }
+
   protected resetView(): void {
     this.view = { x: 0, y: 0, zoom: 1 };
   }
diff --git a/src/editor/viewport/SceneViewport.ts b/src/editor/viewport/SceneViewport.ts
index c96b0c21..d9371559 100644
--- a/src/editor/viewport/SceneViewport.ts
+++ b/src/editor/viewport/SceneViewport.ts
@@ -39,7 +39,7 @@ import type { CellRect } from '../../core/model/tilemapCollision';
 import { footprintCorners } from '../../core/properties/bounds';
 import { localMatrixOf, parentTransform, transformOf } from '../../core/properties/transform';
 import { type EditorState, objectSelection, type TilemapTool } from '../state';
-import { paintedLayerId } from '../inspector/tilemapSection';
+import { paintedLayerId, paintedTilemap } from '../panels/TilemapPanel';
 import { activeDrag, drawBand, drawGrid, endDrag, onDragChange, Theme, textStyle } from '../../ui';
 import { collectHolderItems, type DrawItem } from '../../viewport/items';
 import type { LayerFocus } from '../../viewport/tilemap';
@@ -187,18 +187,15 @@ export class SceneViewport extends FreeViewport {
   }
 
   /**
-   * The selected tilemap shows its layers the way the inspector asks (#138), whatever the tool:
-   * the painted layer is worth seeing alone before the brush is taken up, too. Every other map,
-   * and this one once it is deselected, is drawn whole.
+   * The painted tilemap shows its layers the way its panel asks (#138), whatever the tool: the
+   * painted layer is worth seeing alone before the brush is taken up, too. Every other map, and
+   * this one once it is deselected, is drawn whole.
    */
   protected override tilemapFocus(item: DrawItem): LayerFocus | null {
     const mode = this.state.tilemapPaint.focus;
-    const s = this.state.selection;
-    if (mode === 'all' || item.type !== 'tilemap' || s?.kind !== 'object' || s.objectId !== item.id)
-      return null;
-    const object = findObject(this.resolved() ?? { objects: [] }, item.id);
-    const asset = object && findAssetOf(this.state.project, object.assetId, 'tilemap');
-    return asset ? { layerId: paintedLayerId(this.state, asset), mode } : null;
+    const target = mode === 'all' ? null : paintedTilemap(this.state);
+    if (!target || target.objectId !== item.id) return null;
+    return { layerId: paintedLayerId(this.state, target.asset), mode };
   }
 
   private onPointerDown(e: FederatedPointerEvent): void {
@@ -344,22 +341,18 @@ export class SceneViewport extends FreeViewport {
   }
 
   /**
-   * The tilemap a click paints on: the primary selection, placed here, with a painting tool
+   * The tilemap a click paints on: the one selected (see `paintedTilemap`), with a painting tool
    * chosen. Anything else – another object, the select tool, a modifier held – leaves the view
    * doing what it always did.
    */
   private paintTargetOf(objectId: string): { item: DrawItem; asset: TilemapAsset; layerId: string } | null {
-    const paint = this.state.tilemapPaint;
-    if (paint.tool === 'select') return null;
-    const s = this.state.selection;
-    if (s?.kind !== 'object' || s.objectId !== objectId) return null;
+    if (this.state.tilemapPaint.tool === 'select') return null;
+    const target = paintedTilemap(this.state);
+    if (!target || target.objectId !== objectId) return null;
     const item = this.lastItems.find((i) => i.id === objectId);
     if (!item || item.type !== 'tilemap') return null;
-    const object = findObject(this.resolved() ?? { objects: [] }, objectId);
-    const asset = object && findAssetOf(this.state.project, object.assetId, 'tilemap');
-    if (!asset) return null;
-    const layerId = paintedLayerId(this.state, asset);
-    return layerId ? { item, asset, layerId } : null;
+    const layerId = paintedLayerId(this.state, target.asset);
+    return layerId ? { item, asset: target.asset, layerId } : null;
   }
 
   /** The cell under a pointer position, in the tilemap's own grid. */
@@ -690,9 +683,9 @@ export class SceneViewport extends FreeViewport {
    * paints blind – and a rectangle drag shows the box it would fill.
    */
   private drawPaintOverlay(items: DrawItem[], view: View): void {
-    const s = this.state.selection;
-    if (this.state.tilemapPaint.tool === 'select' || s?.kind !== 'object') return;
-    const item = items.find((i) => i.id === s.objectId && i.type === 'tilemap');
+    const target = this.state.tilemapPaint.tool === 'select' ? null : paintedTilemap(this.state);
+    if (!target) return;
+    const item = items.find((i) => i.id === target.objectId && i.type === 'tilemap');
     if (!item) return;
     const tile = tilemapTileSize(item.props);
     const columns = tilemapColumns(item.props);
diff --git a/tests/editor/painted-tilemap.test.ts b/tests/editor/painted-tilemap.test.ts
new file mode 100644
index 00000000..82515a1e
--- /dev/null
+++ b/tests/editor/painted-tilemap.test.ts
@@ -0,0 +1,71 @@
+/**
+ * Which tilemap the painting panel and the scene view's brush work on (#142): exactly one placed
+ * map, selected in the active scene. Everything else – nothing, two objects, the asset itself, a
+ * map in a scene that is not showing – leaves nothing to paint.
+ */
+import { describe, expect, it } from 'vitest';
+import { CreateAssetCommand } from '../../src/core/commands/assetCommands';
+import { PlaceAssetCommand } from '../../src/core/commands/sceneObjectCommands';
+import { createEmptyProject } from '../../src/core/model/Project';
+import { paintedTilemap } from '../../src/editor/panels/TilemapPanel';
+import { EditorState, objectSelection } from '../../src/editor/state';
+
+function setup() {
+  const state = new EditorState();
+  state.loadProject(createEmptyProject('p', 'P'), 1);
+  const create = (type: 'tilemap' | 'sprite' | 'scene', name: string) => {
+    const command = new CreateAssetCommand(type, name);
+    expect(state.execute(command)).toBe(true);
+    return command.asset.id;
+  };
+  // The first scene there is becomes the active one by itself.
+  const sceneId = create('scene', 'Main');
+  expect(state.activeScene?.id).toBe(sceneId);
+  const place = (holderId: string, assetId: string) => {
+    const command = new PlaceAssetCommand(holderId, assetId, { x: 0, y: 0 });
+    expect(state.execute(command)).toBe(true);
+    return command.objectId;
+  };
+  const tilemapId = create('tilemap', 'Ground');
+  return { state, sceneId, tilemapId, create, place };
+}
+
+describe('the painted tilemap', () => {
+  it('is the one placed map selected in the active scene', () => {
+    const { state, sceneId, tilemapId, place } = setup();
+    const map = place(sceneId, tilemapId);
+    state.select(objectSelection(sceneId, [map]));
+    expect(paintedTilemap(state)).toMatchObject({ objectId: map, asset: { id: tilemapId } });
+  });
+
+  it('is none without a selection, for another object and for the asset itself', () => {
+    const { state, sceneId, tilemapId, create, place } = setup();
+    expect(paintedTilemap(state)).toBeNull();
+    const sprite = place(sceneId, create('sprite', 'Box'));
+    state.select(objectSelection(sceneId, [sprite]));
+    expect(paintedTilemap(state)).toBeNull();
+    state.select({ kind: 'asset', assetId: tilemapId });
+    expect(paintedTilemap(state)).toBeNull();
+  });
+
+  it('is none while a second object is selected with it, map or not', () => {
+    const { state, sceneId, tilemapId, create, place } = setup();
+    const map = place(sceneId, tilemapId);
+    const other = place(sceneId, tilemapId);
+    const sprite = place(sceneId, create('sprite', 'Box'));
+    state.select(objectSelection(sceneId, [map, other], map));
+    expect(paintedTilemap(state)).toBeNull();
+    state.select(objectSelection(sceneId, [map, sprite], map));
+    expect(paintedTilemap(state)).toBeNull();
+    state.select(objectSelection(sceneId, [map]));
+    expect(paintedTilemap(state)?.objectId).toBe(map);
+  });
+
+  it('is none for a map in a scene that is not the one showing', () => {
+    const { state, tilemapId, create, place } = setup();
+    const otherScene = create('scene', 'Elsewhere');
+    const map = place(otherScene, tilemapId);
+    state.select(objectSelection(otherScene, [map]));
+    expect(paintedTilemap(state)).toBeNull();
+  });
+});
diff --git a/tools/e2e/40-tilemap.mjs b/tools/e2e/40-tilemap.mjs
index 12958f85..9c515d1b 100644
--- a/tools/e2e/40-tilemap.mjs
+++ b/tools/e2e/40-tilemap.mjs
@@ -18,29 +18,38 @@ const COLUMNS = 6;
 const ROWS = 4;
 
 /**
- * A widget of the painting section, scrolled into the inspector first. The section sits below the
- * rows of the object, so on this window it starts out below the panel – and a click on a point
- * outside the panel lands on whatever is drawn there instead.
+ * A widget of the tilemap panel (#142), scrolled into view first. On a short window the layers sit
+ * below the fold – and a click on a point outside the panel lands on whatever is drawn there instead.
  */
-async function inInspector(t, hook) {
-  const anchor = await t.json("__gm.inspectorField('Columns')");
+async function inPanel(t, hook) {
   for (let i = 0; i < 15; i++) {
-    const rect = await t.json('__gm.inspectorRect()');
+    const rect = (await t.json('__gm.tilemap.panel()')).panel;
+    if (!rect) return null;
     const point = await t.json(hook);
     if (point && point.y > rect.y + 8 && point.y < rect.y + rect.h - 8) return point;
-    await t.wheel(anchor.x, anchor.y, 200);
+    await t.wheel(rect.x + rect.w / 2, rect.y + rect.h / 2, point && point.y < rect.y ? -200 : 200);
     await t.settle();
   }
   return null;
 }
 
 /** Clicks such a widget; returns false when it could not be brought into view. */
-async function clickInInspector(t, hook) {
-  const point = await inInspector(t, hook);
+async function clickInPanel(t, hook) {
+  const point = await inPanel(t, hook);
   if (point) await t.click(point.x, point.y);
   return Boolean(point);
 }
 
+/** Whether a box lies inside another, give or take a pixel of rounding. */
+function inside(inner, outer) {
+  return (
+    inner.x >= outer.x - 1 &&
+    inner.y >= outer.y - 1 &&
+    inner.x + inner.w <= outer.x + outer.w + 1 &&
+    inner.y + inner.h <= outer.y + outer.h + 1
+  );
+}
+
 /** The four quarters of the cell, read in one call: a running animation must not step between them. */
 async function cellQuarters(t, x, y) {
   const centre = await t.json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, ${x}, ${y})`);
@@ -122,22 +131,59 @@ export async function tilemap(t) {
       overrides: {}, parentId: '', instanceEdits: {} });
     __gm.lookAt(0, ${LANE});`);
   await settle();
+  const unselected = await json('__gm.tilemap.panel()');
+  const cellUnselected = await json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, 0, 0)`);
   await select({ kind: 'object', holderId: 'scene1', objectIds: [MAP_OBJECT], objectId: MAP_OBJECT });
   await settle();
 
-  // 40b. The inspector paints: a tool, the tiles of the project, the layers.
+  // 40b. Painting has a panel of its own beside the scene view (#142): tools, tiles and layers.
+  const panel = await json('__gm.tilemap.panel()');
+  const inspectorRect = await json('__gm.inspectorRect()');
+  check(
+    'selecting a placed tilemap opens the tilemap panel between the scene view and the inspector',
+    !unselected.shown &&
+      panel.shown &&
+      panel.title === 'Tilemap · Tilemap' &&
+      Math.abs(panel.panel.w - inspectorRect.w) <= 1 &&
+      panel.viewport.x + panel.viewport.w <= panel.panel.x &&
+      panel.panel.x + panel.panel.w <= inspectorRect.x &&
+      Math.abs(panel.panel.y - panel.viewport.y) <= 1 &&
+      Math.abs(panel.panel.h - panel.viewport.h) <= 1 &&
+      panel.viewport.w < unselected.viewport.w,
+    JSON.stringify({ unselected, panel, inspectorRect }),
+  );
   const section = await json(
     '(() => ({ tools: __gm.tilemap.toolAt("brush") !== null, grass: __gm.tilemap.tileButtonAt("at-grass") !== null,' +
       ' layers: (__gm.tilemap.layerRowAt(0) || {}).id }))()',
   );
+  // The view keeps the world where it is on screen, rather than its centre, which shifted the map
+  // by half the panel's width.
+  const cellWithPanel = await json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, 0, 0)`);
   check(
-    'a selected tilemap offers tools, tiles and layers in the inspector',
-    section.tools && section.grass && Boolean(section.layers),
-    JSON.stringify(section),
+    'the map stays put on screen when the panel opens',
+    Math.abs(cellWithPanel.x - cellUnselected.x) <= 1 && Math.abs(cellWithPanel.y - cellUnselected.y) <= 1,
+    JSON.stringify({ cellUnselected, cellWithPanel }),
   );
+  // Staying put leaves the right of the map behind the panel; the steps below paint across it.
+  await evaluate(`__gm.lookAt(0, ${LANE})`);
+  await settle();
+  // Found by its title rather than a hook: whatever is left of the section in the inspector would
+  // have no hook pointing at it any more.
+  const paintingTitles = await json('__gm.locateAll("PAINTING")');
+  check(
+    'the panel offers tools, tiles and layers, and the inspector no longer does',
+    section.tools &&
+      section.grass &&
+      Boolean(section.layers) &&
+      paintingTitles.length === 1 &&
+      inside({ ...paintingTitles[0], w: 0, h: 0 }, panel.panel) &&
+      Boolean(await json("__gm.inspectorField('Columns')")),
+    JSON.stringify({ section, paintingTitles }),
+  );
+  await shot('40-tilemap-panel');
   // The tiles are a grid of pictures (#139), and each shows its block's lone tile: the four convex
   // corners, read off the palette in one call like a cell of the map.
-  await inInspector(t, '__gm.tilemap.tileButtonAt("at-grass")');
+  await inPanel(t, '__gm.tilemap.tileButtonAt("at-grass")');
   const swatch = await json(`(() => {
     const s = __gm.tilemap.tileSwatch("at-grass");
     if (!s) return null;
@@ -158,16 +204,16 @@ export async function tilemap(t) {
     JSON.stringify({ swatch, want: lone }),
   );
   check(
-    'and puts several tiles side by side in the inspector',
+    'and puts several tiles side by side in the panel',
     swatch !== null && swatch.columns >= 3,
     JSON.stringify(swatch),
   );
   // Clicked through the hook rather than by its text: the tile's own row in the asset panel
   // reads "Grass" as well, and a click there would only select the tile.
   check(
-    'the tile can be picked in the section',
-    await clickInInspector(t, '__gm.tilemap.tileButtonAt("at-grass")'),
-    JSON.stringify(await json('__gm.inspectorRect()')),
+    'the tile can be picked in the panel',
+    await clickInPanel(t, '__gm.tilemap.tileButtonAt("at-grass")'),
+    JSON.stringify(await json('__gm.tilemap.panel()')),
   );
   await settle();
   const paint = await json('__gm.tilemap.paint()');
@@ -208,7 +254,7 @@ export async function tilemap(t) {
   );
 
   // 40d. The rectangle tool fills the box a drag spans.
-  await clickInInspector(t, '__gm.tilemap.toolAt("rect")');
+  await clickInPanel(t, '__gm.tilemap.toolAt("rect")');
   await settle();
   const corner = await json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, 0, 0)`);
   const far = await json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, 2, 2)`);
@@ -257,7 +303,7 @@ export async function tilemap(t) {
   );
 
   // 40g. Erasing takes cells out again.
-  await clickInInspector(t, '__gm.tilemap.toolAt("erase")');
+  await clickInPanel(t, '__gm.tilemap.toolAt("erase")');
   await settle();
   const one = await json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, 2, 2)`);
   await click(one.x, one.y);
@@ -272,7 +318,7 @@ export async function tilemap(t) {
   await settle();
 
   // 40h. A second layer draws above the first, and hiding it leaves its cells alone.
-  await clickInInspector(t, '__gm.tilemap.addLayerAt()');
+  await clickInPanel(t, '__gm.tilemap.addLayerAt()');
   await settle();
   let layers = await json(`__gm.tilemap.layers(${JSON.stringify(made.id)})`);
   check(
@@ -280,7 +326,7 @@ export async function tilemap(t) {
     layers.length === 2 && layers[1].cells === 0,
     JSON.stringify(layers),
   );
-  await clickInInspector(t, '__gm.tilemap.tileButtonAt("at-grass")');
+  await clickInPanel(t, '__gm.tilemap.tileButtonAt("at-grass")');
   await settle();
   const above = await json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, 4, 0)`);
   await click(above.x, above.y);
@@ -293,7 +339,7 @@ export async function tilemap(t) {
   );
   // Hiding the upper layer (the list is drawn top-down, newest first) leaves its cell in the model
   // and takes it out of the drawing.
-  const row = await inInspector(t, '__gm.tilemap.layerRowAt(0)');
+  const row = await inPanel(t, '__gm.tilemap.layerRowAt(0)');
   if (row) await click(row.visible.x, row.visible.y);
   await settle();
   const hidden = await json(`__gm.tilemap.layers(${JSON.stringify(made.id)})`);
@@ -309,7 +355,7 @@ export async function tilemap(t) {
   // 40m. The painted layer is named in the field below the list, and Show singles it out in the
   //      scene view (#138). It sits here, not at the end, because here both layers exist: the upper
   //      one is painted on and holds the cell (4,0), the lower one the 3 × 3 block.
-  const nameField = await inInspector(t, '__gm.tilemap.layerNameAt()');
+  const nameField = await inPanel(t, '__gm.tilemap.layerNameAt()');
   if (nameField) {
     await click(nameField.x, nameField.y);
     await press('a', { ctrl: true });
@@ -338,7 +384,7 @@ export async function tilemap(t) {
   const upperWhole = await quarter(4, 0);
   /** Chooses an entry of the Show dropdown: the topmost hit, which is the open menu. */
   const show = async (label) => {
-    const button = await inInspector(t, '__gm.tilemap.focusAt()');
+    const button = await inPanel(t, '__gm.tilemap.focusAt()');
     if (button) await click(button.x, button.y);
     await settle();
     const entry = await t.locate(label, true);
@@ -372,6 +418,10 @@ export async function tilemap(t) {
   );
 
   // Only the selected map is singled out; deselected it is drawn whole, and the model never changed.
+  // The brush is taken up first, so the deselection has a tool to put down (#142).
+  await evaluate("__gm.state.setTilemapPaint({ tool: 'brush' })");
+  const paintBefore = await json('__gm.tilemap.paint()');
+  const cellSelected = await json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, 0, 0)`);
   await evaluate('__gm.state.select(null)');
   await settle();
   const deselected = await quarter(1, 1);
@@ -381,7 +431,56 @@ export async function tilemap(t) {
     colourDistance(deselected, lowerWhole) <= 12 && layers.every((l) => !l.hidden),
     JSON.stringify({ deselected, lowerWhole, layers }),
   );
+  const gone = await json('__gm.tilemap.panel()');
+  const cellGone = await json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, 0, 0)`);
+  const paintAfter = await json('__gm.tilemap.paint()');
+  check(
+    'deselecting closes the panel, gives the scene view its room back and puts the brush down',
+    !gone.shown &&
+      gone.viewport.w > panel.viewport.w &&
+      Math.abs(cellGone.x - cellSelected.x) <= 1 &&
+      Math.abs(cellGone.y - cellSelected.y) <= 1 &&
+      paintAfter.tool === 'select' &&
+      paintAfter.tileId === paintBefore.tileId &&
+      paintAfter.layerId === paintBefore.layerId,
+    JSON.stringify({ gone, cellSelected, cellGone, paintBefore, paintAfter }),
+  );
+
+  // Two objects selected are no single map to paint, even when both are tilemaps; and the panel
+  // belongs to the scene tab, so another tab takes it along while the map stays selected.
+  const second = await json(
+    `__gm.state.activeScene.objects.find((o) => o.id !== ${JSON.stringify(MAP_OBJECT)} && !o.parentId).id`,
+  );
+  await select({ kind: 'object', holderId: 'scene1', objectIds: [MAP_OBJECT, second], objectId: MAP_OBJECT });
+  await settle();
+  const withTwo = (await json('__gm.tilemap.panel()')).shown;
   await select({ kind: 'object', holderId: 'scene1', objectIds: [MAP_OBJECT], objectId: MAP_OBJECT });
+  await settle();
+  await openTab(t, 'graph');
+  await settle();
+  const onOtherTab = (await json('__gm.tilemap.panel()')).shown;
+  await openTab(t, 'scene');
+  await settle();
+  const back = await json('__gm.tilemap.panel()');
+  check(
+    'the panel stays away with two objects selected and on another tab, and comes back with the scene',
+    withTwo === false && onOtherTab === false && back.shown && Math.abs(back.panel.w - panel.panel.w) <= 1,
+    JSON.stringify({ second, withTwo, onOtherTab, back }),
+  );
+  const cellBack = await json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, 0, 0)`);
+  await drag(back.splitter.x, back.splitter.y, back.splitter.x - 60, back.splitter.y);
+  await settle();
+  const wider = await json('__gm.tilemap.panel()');
+  const cellWider = await json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, 0, 0)`);
+  check(
+    'the splitter widens the panel at the expense of the scene view, and the map stays put',
+    Math.abs(wider.panel.w - back.panel.w - 60) <= 1 &&
+      Math.abs(back.viewport.w - wider.viewport.w - 60) <= 1 &&
+      Math.abs(cellWider.x - cellBack.x) <= 1,
+    JSON.stringify({ back, wider, cellBack, cellWider }),
+  );
+  await drag(wider.splitter.x, wider.splitter.y, wider.splitter.x + 60, wider.splitter.y);
+  await settle();
   await show('All layers');
   await mutate(
     "__gm.state.project.assets.find((a) => a.id === 'at-grass').pictures = ['at-floor-1', 'at-floor-2']",
@@ -390,7 +489,7 @@ export async function tilemap(t) {
   await settle();
 
   // 40i. Back to Select: the map is moved again instead of painted on.
-  await clickInInspector(t, '__gm.tilemap.toolAt("select")');
+  await clickInPanel(t, '__gm.tilemap.toolAt("select")');
   await settle();
   const before = (await t.object(MAP_OBJECT)).position;
   const grab = await json(`__gm.tilemap.cellAt(${JSON.stringify(MAP_OBJECT)}, 2, 1)`);