An animation reaches the scene's own background and objects inside placed containers (#109)

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/model/animation.ts

@@ -2,6 +2,8 @@ import { isKindWith } from '../properties/kinds';
 import { type PropertyDef, schemaFor } from '../properties/PropertySchema';
 import type { AnimationAsset, AnimationKey, AnimationTrack, Asset } from './Asset';
 import type { AssetType } from './AssetTypes';
+import { treeOrder } from './hierarchy';
+import { instanceChildId, resolveObjects } from './instance';
 import { findAsset, type Project } from './Project';
 import { colorOf, type PropertyValue, textOf } from './Properties';
 import type { SceneObject } from './SceneObject';
@@ -151,29 +153,71 @@ export function trackWriteAt(
 
 /** The kind a row's property has on an asset of that type; undefined for one the timeline cannot animate. */
 export function animatedKind(type: AssetType, key: string): string | undefined {
-  if (isPositionKey(key)) return 'number';
   return animatableDefs(type).find((d) => d.key === key)?.kind;
 }
 
 /**
  * The rows the timeline offers for an asset type: position, then the schema's flat properties. A
- * list or struct has no single value to key; a shader's own parameters come later (#97).
+ * list or struct has no single value to key; a shader's own parameters come later (#97). A scene is
+ * placed nowhere, so it offers only its own properties.
  */
 export function animatableDefs(type: AssetType): PropertyDef[] {
-  if (type === 'scene') return [];
+  const own = schemaFor(type).filter((d) => d.kind !== 'list' && d.kind !== 'struct');
+  if (type === 'scene') return own;
   const position: PropertyDef[] = POSITION_KEYS.map((key) => ({
     key,
     label: key.toUpperCase(),
     kind: 'number',
     default: 0,
   }));
-  const own = schemaFor(type).filter((d) => d.kind !== 'list' && d.kind !== 'struct');
   return [...position, ...own];
 }
 
-/** The objects a row may aim at below the root: a container's or scene's whole tree, nothing for the rest. */
-export function rootObjects(root: Asset | undefined): readonly SceneObject[] {
-  return root && (root.type === 'container' || root.type === 'scene') ? root.objects : [];
+/**
+ * The id of the one object a placed root stands on – the preview's holder, and the instance the
+ * targets inside a container are resolved below.
+ */
+export const PLACED_ROOT_ID = 'preview-root';
+
+/** The root placed at the origin, its content following the template like any placed container's. */
+export function placedRoot(root: Asset): SceneObject {
+  return {
+    id: PLACED_ROOT_ID,
+    assetId: root.id,
+    name: root.name,
+    position: { x: 0, y: 0, z: 0 },
+    editorOffset: { x: 0, y: 0 },
+    overrides: {},
+    parentId: '',
+    instanceEdits: {},
+  };
+}
+
+/** One object a row may aim at below the root, under the id the row stores. */
+export interface AnimationTarget {
+  id: string;
+  object: SceneObject;
+  depth: number;
+}
+
+/**
+ * Everything a row may aim at below the root, in tree order – into placed containers, too (#109).
+ * A scene's rows name its objects by the ids the running scene gives them, which a baked instance
+ * keeps. A container's rows name a path of template ids, what the runtime appends to whichever
+ * object the animation plays on. A sprite or text has nothing below it.
+ */
+export function animationTargets(project: Project, root: Asset | undefined): AnimationTarget[] {
+  if (root?.type === 'scene')
+    return treeOrder({ objects: resolveObjects(project, root) }).map(({ object, depth }) => ({
+      id: object.id,
+      object,
+      depth,
+    }));
+  if (root?.type !== 'container') return [];
+  const prefix = instanceChildId(PLACED_ROOT_ID, '');
+  return treeOrder({ objects: resolveObjects(project, { objects: [placedRoot(root)] }) })
+    .filter(({ object }) => object.id.startsWith(prefix))
+    .map(({ object, depth }) => ({ id: object.id.slice(prefix.length), object, depth: depth - 1 }));
 }
 
 /** The asset a row aims at: the root itself, or what the object inside it places. Undefined once gone. */
@@ -184,21 +228,20 @@ export function targetAssetOf(
 ): Asset | undefined {
   const root = findAsset(project, animation.root);
   if (target === '') return root;
-  const object = rootObjects(root).find((o) => o.id === target);
-  return object ? findAsset(project, object.assetId) : undefined;
+  const aimed = animationTargets(project, root).find((t) => t.id === target);
+  return aimed ? findAsset(project, aimed.object.assetId) : undefined;
 }
 
 /** How the timeline names what a row aims at: the object (or the root itself) and the property. */
 export function trackLabel(project: Project, animation: AnimationAsset, track: AnimationTrack): string {
   const root = findAsset(project, animation.root);
-  const object = track.target === '' ? undefined : rootObjects(root).find((o) => o.id === track.target);
-  const aimed = targetAssetOf(project, animation, track.target);
-  const who =
+  const object =
     track.target === ''
-      ? (root?.name ?? '?')
-      : object
-        ? object.name || findAsset(project, object.assetId)?.name || '?'
-        : '(missing)';
+      ? undefined
+      : animationTargets(project, root).find((t) => t.id === track.target)?.object;
+  const aimed = object ? findAsset(project, object.assetId) : track.target === '' ? root : undefined;
+  const who =
+    track.target === '' ? (root?.name ?? '?') : object ? object.name || aimed?.name || '?' : '(missing)';
   const def = aimed && animatableDefs(aimed.type).find((d) => d.key === track.property);
   return `${who} · ${def?.label ?? track.property}`;
 }

src/core/model/animationPreview.ts

@@ -3,24 +3,33 @@
  * the playhead written over it. Nothing here touches the document – the holder returned is built
  * fresh on every call from copies, and the preview draws it the way the Scene tab draws a scene.
  */
-import { animatedKind, frameCount, isPositionKey, playbackOf, rootObjects, trackWriteAt } from './animation';
+import {
+  animatableDefs,
+  animatedKind,
+  frameCount,
+  isPositionKey,
+  PLACED_ROOT_ID,
+  placedRoot,
+  playbackOf,
+  trackWriteAt,
+} from './animation';
 import type { AnimationAsset, AnimationTrack, Asset } from './Asset';
-import { type InstanceEdit, instanceChildId } from './instance';
+import { instanceChildId, objectRef } from './instance';
 import { findAsset, type ObjectHolder, type Project } from './Project';
 import type { PropertyValue } from './Properties';
 import { resolveSceneObjectProps } from '../properties/resolve';
 import type { SceneObject } from './SceneObject';
 
 /** The one object the preview places the root on – what a row aimed at the root itself writes to. */
-export const PREVIEW_ROOT_ID = 'preview-root';
+export const PREVIEW_ROOT_ID = PLACED_ROOT_ID;
 
 /**
- * The holder the preview draws at `frame`: the scene itself for a scene root, otherwise a holder
+ * The holder the preview draws at `frame`: a copy of the scene for a scene root, otherwise a holder
  * of one object placing the root at the origin, its content resolved from the template like any
- * placed container's. Rows reach the root through that object and its children through the
- * object's instance edits – the same route a placed container's content takes. `undefined`
- * without a root. Past the end of a `once-reset` pass nothing is written: the player has put the
- * starting values back by then.
+ * placed container's. A row reaches an object stored in the holder directly and one resolved from a
+ * container through its instance's edits – the same route an edit in the Scene tab takes, so a row
+ * aimed into a placed container needs nothing of its own (#109). `undefined` without a root. Past
+ * the end of a `once-reset` pass nothing is written: the player has put the starting values back.
  */
 export function previewHolder(
   project: Project,
@@ -30,10 +39,12 @@ export function previewHolder(
   const root = findAsset(project, animation.root);
   if (!root) return undefined;
   const reset = playbackOf(animation) === 'once-reset' && frame >= frameCount(animation);
-  const tracks = reset ? [] : animation.tracks;
-  return root.type === 'scene'
-    ? sceneAt(project, tracks, root, frame)
-    : placedAt(project, tracks, root, frame);
+  const holder = root.type === 'scene' ? sceneCopy(root) : placedHolder(root);
+  for (const track of reset ? [] : animation.tracks) {
+    if (root.type === 'scene' && track.target === '') writeScene(holder, track, frame);
+    else writeObject(project, holder, previewObjectId(root, track.target), track, frame);
+  }
+  return holder;
 }
 
 /** The id the preview draws a row's target under – for a check that wants to look at it. */
@@ -42,70 +53,48 @@ export function previewObjectId(root: Asset | undefined, target: string): string
   return target === '' ? PREVIEW_ROOT_ID : instanceChildId(PREVIEW_ROOT_ID, target);
 }
 
-function sceneAt(
-  project: Project,
-  tracks: readonly AnimationTrack[],
-  root: ObjectHolder,
-  frame: number,
-): ObjectHolder {
-  const objects = root.objects.map((o) => ({
-    ...o,
-    position: { ...o.position },
-    overrides: { ...o.overrides },
-  }));
-  const byId = new Map(objects.map((o) => [o.id, o]));
-  for (const track of tracks) {
-    const object = byId.get(track.target);
-    const asset = object && findAsset(project, object.assetId);
-    const kind = asset && animatedKind(asset.type, track.property);
-    if (!object || !asset || !kind) continue;
-    const base = isPositionKey(track.property)
-      ? object.position[track.property]
-      : resolveSceneObjectProps(project, asset, object)[track.property];
-    const value = trackWriteAt(track, kind, frame, base);
-    if (value === undefined) continue;
-    if (isPositionKey(track.property)) object.position[track.property] = Number(value);
-    else object.overrides[track.property] = value;
-  }
-  return { ...root, objects };
+/** Deep enough that nothing a row writes – a position, an override, an instance edit – is the document's. */
+function sceneCopy(scene: ObjectHolder): ObjectHolder {
+  return {
+    ...scene,
+    props: { ...scene.props },
+    objects: scene.objects.map((o) => ({
+      ...o,
+      position: { ...o.position },
+      overrides: { ...o.overrides },
+      instanceEdits: structuredClone(o.instanceEdits),
+    })),
+  };
 }
 
-function placedAt(
+function placedHolder(root: Asset): ObjectHolder {
+  return { id: PREVIEW_ROOT_ID, type: 'container', name: root.name, props: {}, objects: [placedRoot(root)] };
+}
+
+/** A row on the scene itself: its value goes into the copy's own properties. */
+function writeScene(holder: ObjectHolder, track: AnimationTrack, frame: number): void {
+  const def = animatableDefs('scene').find((d) => d.key === track.property);
+  if (!def) return;
+  const value = trackWriteAt(track, def.kind, frame, holder.props[track.property] ?? def.default);
+  if (value !== undefined) holder.props[track.property] = value;
+}
+
+function writeObject(
   project: Project,
-  tracks: readonly AnimationTrack[],
-  root: Asset,
+  holder: ObjectHolder,
+  id: string,
+  track: AnimationTrack,
   frame: number,
-): ObjectHolder {
-  const placed: SceneObject = {
-    id: PREVIEW_ROOT_ID,
-    assetId: root.id,
-    name: root.name,
-    position: { x: 0, y: 0, z: 0 },
-    editorOffset: { x: 0, y: 0 },
-    overrides: {},
-    parentId: '',
-    instanceEdits: {},
-  };
-  const templates = rootObjects(root);
-  for (const track of tracks) {
-    const template = track.target === '' ? undefined : templates.find((o) => o.id === track.target);
-    const aimed = track.target === '' ? root : template && findAsset(project, template.assetId);
-    const kind = aimed && animatedKind(aimed.type, track.property);
-    if (!aimed || !kind) continue;
-    const base = template
-      ? baseOf(project, aimed, template, track.property)
-      : baseOf(project, aimed, placed, track.property);
-    const value = trackWriteAt(track, kind, frame, base);
-    if (value === undefined) continue;
-    if (!template) writeTo(placed, track.property, value);
-    else
-      writeEdit(
-        (placed.instanceEdits[template.id] ??= { position: {}, overrides: {} }),
-        track.property,
-        value,
-      );
-  }
-  return { id: PREVIEW_ROOT_ID, type: 'container', name: root.name, props: {}, objects: [placed] };
+): void {
+  const ref = objectRef(project, holder, id);
+  const asset = ref && findAsset(project, ref.object.assetId);
+  const kind = asset && animatedKind(asset.type, track.property);
+  if (!ref || !asset || !kind) return;
+  const value = trackWriteAt(track, kind, frame, baseOf(project, asset, ref.object, track.property));
+  if (value === undefined) return;
+  if (isPositionKey(track.property))
+    ref.setPosition({ ...ref.object.position, [track.property]: Number(value) });
+  else ref.setOverride(track.property, value);
 }
 
 /** What the target holds before the animation writes it: the zero of a relative row. */
@@ -113,13 +102,3 @@ function baseOf(project: Project, asset: Asset, object: SceneObject, key: string
   if (isPositionKey(key)) return object.position[key];
   return resolveSceneObjectProps(project, asset, object)[key];
 }
-
-function writeTo(object: SceneObject, key: string, value: PropertyValue): void {
-  if (isPositionKey(key)) object.position[key] = Number(value);
-  else object.overrides[key] = value;
-}
-
-function writeEdit(edit: InstanceEdit, key: string, value: PropertyValue): void {
-  if (isPositionKey(key)) edit.position[key] = Number(value);
-  else edit.overrides[key] = value;
-}

src/editor/animation/RowDialog.ts

@@ -2,9 +2,8 @@ import {
   AddAnimationTrackCommand,
   RetargetAnimationTrackCommand,
 } from '../../core/commands/animationCommands';
-import { animatableDefs, animatedKind, rootObjects, targetAssetOf } from '../../core/model/animation';
+import { animatableDefs, animatedKind, animationTargets, targetAssetOf } from '../../core/model/animation';
 import type { AnimationAsset, AnimationTrack } from '../../core/model/Asset';
-import { treeOrder } from '../../core/model/hierarchy';
 import { findAsset } from '../../core/model/Project';
 import type { PropertyDef } from '../../core/properties/PropertySchema';
 import { Button, Dropdown, HStack, Label, Menu, type MenuItem, Popup, Spacer, Theme } from '../../ui';
@@ -126,12 +125,11 @@ export class RowDialog extends Popup {
     const root = findAsset(this.state.project, this.asset.root);
     if (!root) return [];
     const choices: TargetChoice[] = [{ id: '', label: `${root.name} (itself)` }];
-    if (root.type === 'container' || root.type === 'scene')
-      for (const { object, depth } of treeOrder(root))
-        choices.push({
-          id: object.id,
-          label: `${'   '.repeat(depth)}${object.name || findAsset(this.state.project, object.assetId)?.name || '?'}`,
-        });
+    for (const { id, object, depth } of animationTargets(this.state.project, root))
+      choices.push({
+        id,
+        label: `${'   '.repeat(depth)}${object.name || findAsset(this.state.project, object.assetId)?.name || '?'}`,
+      });
     return choices;
   }
 
@@ -166,9 +164,7 @@ export class RowDialog extends Popup {
         this.refresh();
       },
     }));
-    new Menu(items, {
-      searchable: rootObjects(findAsset(this.state.project, this.asset.root)).length > 8,
-    }).openBelow(this.targetButton);
+    new Menu(items, { searchable: items.length > 9 }).openBelow(this.targetButton);
   }
 
   private openProperties(): void {

src/runtime/World.ts

@@ -1,6 +1,7 @@
 import { ENTITY_HANDLE, isHandleEnabled, type PointerState, worldMatrixOf } from '../core/graph';
 import { newId } from '../core/ids';
 import type { Asset } from '../core/model/Asset';
+import type { PropertyBag } from '../core/model/Properties';
 import { isPlaceableType } from '../core/model/AssetTypes';
 import { bakeInstances, materializeInstance, objectRef, resolveObjects } from '../core/model/instance';
 import { treeOrder } from '../core/model/hierarchy';
@@ -34,7 +35,8 @@ export interface ModelWrite {
  */
 export class World {
   readonly entities: Entity[] = [];
-  backgroundColor = 0x000000;
+  /** The running scene's own properties – read from the model, and written by an animation over the scene. */
+  readonly sceneProps: PropertyBag = {};
   /** Set by a behavior (Stop game node); the editor leaves play mode on the next tick. */
   stopRequested = false;
   /** Set by a behavior (Restart game node); the editor restarts the scene on the next tick. */
@@ -83,6 +85,11 @@ export class World {
     return this.elapsed;
   }
 
+  get backgroundColor(): number {
+    const background = this.sceneProps.backgroundColor;
+    return typeof background === 'number' ? background : 0x000000;
+  }
+
   /** Makes the entities match the scene; props are updated in place so systems holding a bag stay current. */
   syncFromModel(): void {
     const scene = findScene(this.project, this.sceneId);
@@ -91,8 +98,7 @@ export class World {
     // behavior destroy one of them for good. Play does it (on its throwaway copy); the editor run
     // must not, so there the content stays resolved and `objectRef` writes into the instance edits.
     if (this.bakeContainers && bakeInstances(this.project, scene)) this.structureChanged = true;
-    const background = scene.props.backgroundColor;
-    this.backgroundColor = typeof background === 'number' ? background : 0x000000;
+    Object.assign(this.sceneProps, scene.props);
     const objects = new Map(resolveObjects(this.project, scene).map((o) => [o.id, o]));
     const keep = new Set<Entity>();
     for (const object of objects.values()) {

src/runtime/systems/AnimationSystem.ts

@@ -21,12 +21,14 @@ export interface AnimationFinish {
   animationId: string;
 }
 
-/** A row that reaches something this tick: the entity it writes and the kind it blends as. */
+/** A row that reaches something this tick: how to read and write it, and the kind it blends as. */
 interface Binding {
   track: AnimationTrack;
-  entity: Entity;
   kind: string;
+  /** Where the player keeps the starting value: `<entity id> <property>`, or `scene <property>`. */
   base: string;
+  read(): PropertyValue;
+  write(value: PropertyValue): void;
 }
 
 /**
@@ -53,18 +55,18 @@ export class AnimationSystem implements System {
       if (!player.bases) {
         // The first tick only takes the starting values and shows frame 0; the clock runs from the next.
         player.bases = {};
-        for (const b of bindings) player.bases[b.base] = read(b.entity, b.track.property);
+        for (const b of bindings) player.bases[b.base] = b.read();
       } else if (player.playing && isHandleEnabled(entity)) player.time += dt;
       const head = animationPlayheadAt(asset, player.time);
       for (const b of bindings) {
         const value = trackWriteAt(b.track, b.kind, head.frame, player.bases[b.base]);
-        if (value !== undefined) write(b.entity, b.track.property, value);
+        if (value !== undefined) b.write(value);
       }
       if (!head.finished) continue;
       if (playbackOf(asset) === 'once-reset')
         for (const b of bindings) {
           const base = player.bases[b.base];
-          if (base !== undefined) write(b.entity, b.track.property, base);
+          if (base !== undefined) b.write(base);
         }
       drop(entity, player);
       this.finished.push({ entity, animationId: asset.id });
@@ -81,32 +83,58 @@ function drop(entity: Entity, player: AnimationPlayer): void {
 }
 
 /**
- * The rows that reach something on this object. A scene's rows aim at its objects by id, and only
- * while that scene runs; everything else aims at the object itself or at what its template placed
- * inside it. A row whose target is gone, or lacks the property, is skipped.
+ * The rows that reach something on this object. A scene's rows aim at the scene itself or at its
+ * objects by id, and only while that scene runs; everything else aims at the object itself or at
+ * what its template placed inside it, however deep. A row whose target is gone, or lacks the
+ * property, is skipped.
  */
 function bind(world: World, asset: AnimationAsset, owner: Entity): Binding[] {
   const root = world.project.assets.find((a) => a.id === asset.root);
   if (!root) return [];
   const bindings: Binding[] = [];
   for (const track of asset.tracks) {
+    const key = track.property;
+    if (root.type === 'scene' && track.target === '') {
+      const kind = world.sceneId === root.id ? animatedKind('scene', key) : undefined;
+      if (kind)
+        bindings.push({
+          track,
+          kind,
+          base: `scene ${key}`,
+          read: () => world.sceneProps[key] ?? 0,
+          write: (value) => {
+            world.sceneProps[key] = value;
+          },
+        });
+      continue;
+    }
     let entity: Entity | undefined;
     if (root.type === 'scene')
-      entity = world.sceneId === root.id && track.target ? world.findByObjectId(track.target) : undefined;
+      entity = world.sceneId === root.id ? world.findByObjectId(track.target) : undefined;
     else if (track.target === '') entity = owner;
     else entity = world.findByObjectId(childId(owner.objectId, track.target));
-    const kind = entity && animatedKind(entity.type, track.property);
-    if (entity && kind) bindings.push({ track, entity, kind, base: `${entity.id} ${track.property}` });
+    const kind = entity && animatedKind(entity.type, key);
+    if (entity && kind) {
+      const aimed = entity;
+      bindings.push({
+        track,
+        kind,
+        base: `${aimed.id} ${key}`,
+        read: () => read(aimed, key),
+        write: (value) => write(aimed, key, value),
+      });
+    }
   }
   return bindings;
 }
 
-/** The id a template object gets below a placed container – nested one deeper when the container is content itself. */
-function childId(ownerId: string, templateId: string): string {
+/**
+ * The id a template object gets below a placed container – nested one deeper when the container is
+ * content itself. `path` may run through containers placed inside the template (`a/b`).
+ */
+function childId(ownerId: string, path: string): string {
   const split = splitInstanceId(ownerId);
-  return split
-    ? instanceChildId(split.instanceId, `${split.path}/${templateId}`)
-    : instanceChildId(ownerId, templateId);
+  return split ? instanceChildId(split.instanceId, `${split.path}/${path}`) : instanceChildId(ownerId, path);
 }
 
 function read(entity: Entity, key: string): PropertyValue {

tests/core/animation-preview.test.ts

@@ -10,6 +10,8 @@ import {
   SetTrackRelativeCommand,
 } from '../../src/core/commands/animationCommands';
 import { CreateAssetCommand } from '../../src/core/commands/assetCommands';
+import { CommandError } from '../../src/core/commands/Command';
+import { animatableDefs, animationTargets, targetAssetOf, trackLabel } from '../../src/core/model/animation';
 import { CreateContainerCommand } from '../../src/core/commands/containerCommands';
 import { RemoveSceneObjectsCommand } from '../../src/core/commands/sceneObjectCommands';
 import { PREVIEW_ROOT_ID, previewHolder, previewObjectId } from '../../src/core/model/animationPreview';
@@ -183,3 +185,86 @@ describe('the preview of an animation over a scene', () => {
     expect(f.sceneOf().objects.find((o) => o.id === box)!.position.y).toBe(2);
   });
 });
+
+/** A sprite packed into `Inner`, `Inner` packed into `Outer`, and `Outer` placed in the scene. */
+function nested() {
+  const f = makeSpriteScene();
+  const arm = place(f, f.spriteId, { x: 10, y: 20 });
+  const inner = new CreateContainerCommand(f.sceneId, [arm]);
+  f.stack.execute(inner);
+  const outer = new CreateContainerCommand(f.sceneId, [inner.objectId]);
+  f.stack.execute(outer);
+  const placing = (findAsset(f.project, outer.assetId) as ContainerAsset).objects[0]!;
+  const armTemplate = (findAsset(f.project, inner.assetId) as ContainerAsset).objects[0]!;
+  return { f, inner, outer, placing, armTemplate, path: `${placing.id}/${armTemplate.id}` };
+}
+
+describe('the reach of a row (#109)', () => {
+  it('offers what a container placed inside the root holds, as a path of template ids', () => {
+    const { f, outer, placing, path } = nested();
+    const targets = animationTargets(f.project, findAsset(f.project, outer.assetId));
+    expect(targets.map((t) => [t.id, t.depth])).toEqual([
+      [placing.id, 0],
+      [path, 1],
+    ]);
+  });
+
+  it('offers a scene the content of its placed containers under the ids the running scene uses', () => {
+    const { f, outer, placing, path } = nested();
+    const targets = animationTargets(f.project, findAsset(f.project, f.sceneId));
+    expect(targets.map((t) => t.id)).toEqual([
+      outer.objectId,
+      instanceChildId(outer.objectId, placing.id),
+      instanceChildId(outer.objectId, path),
+    ]);
+  });
+
+  it('draws a row aimed into a nested container on the child, through the instance edits of a copy', () => {
+    const { f, outer, path, armTemplate } = nested();
+    const walk = addAnimation(f, outer.assetId);
+    addRow(f, walk, 'x', [[0, 55]], path);
+    const before = JSON.stringify(f.project);
+    const child = drawn(f, current(f, walk.id), 0).get(instanceChildId(PREVIEW_ROOT_ID, path))!;
+    expect(child.position).toEqual({ ...armTemplate.position, x: 55 });
+    expect(JSON.stringify(f.project)).toBe(before);
+  });
+
+  it('draws a scene row aimed into a placed container without writing the scene', () => {
+    const { f, outer, path } = nested();
+    const id = instanceChildId(outer.objectId, path);
+    const walk = addAnimation(f, f.sceneId);
+    addRow(f, walk, 'y', [[0, 300]], id);
+    const before = JSON.stringify(f.project);
+    const holder = previewHolder(f.project, current(f, walk.id), 0)!;
+    expect(resolveObjects(f.project, holder).find((o) => o.id === id)!.position.y).toBe(300);
+    expect(JSON.stringify(f.project)).toBe(before);
+  });
+
+  it("keys the scene's own properties on the scene itself", () => {
+    const f = makeSpriteScene();
+    const walk = addAnimation(f, f.sceneId);
+    expect(animatableDefs('scene').map((d) => d.key)).toEqual(['backgroundColor']);
+    expect(() => f.stack.execute(new AddAnimationTrackCommand(walk.id, '', 'x'))).toThrow(CommandError);
+    addRow(f, walk, 'backgroundColor', [
+      [0, 0x000000],
+      [10, 0xff0000],
+    ]);
+    const before = f.sceneOf().props.backgroundColor;
+    const holder = previewHolder(f.project, current(f, walk.id), 5)!;
+    expect(holder.props.backgroundColor).toBe(0x800000);
+    expect(collectHolderItems(f.project, holder, 0).background).toBe(0x800000);
+    expect(f.sceneOf().props.backgroundColor).toBe(before);
+  });
+
+  it('reads a row as missing once the template loses its target, and keeps its keys', () => {
+    const { f, outer, inner, path, armTemplate } = nested();
+    const walk = addAnimation(f, outer.assetId);
+    const row = addRow(f, walk, 'x', [[0, 55]], path);
+    f.stack.execute(new RemoveSceneObjectsCommand(inner.assetId, [armTemplate.id]));
+    const now = current(f, walk.id);
+    const track = now.tracks.find((t) => t.id === row)!;
+    expect(targetAssetOf(f.project, now, path)).toBeUndefined();
+    expect(trackLabel(f.project, now, track)).toBe('(missing) · x');
+    expect(track.keys).toEqual([{ frame: 0, value: 55 }]);
+  });
+});

tests/core/animation.test.ts

@@ -414,6 +414,75 @@ describe('the AnimationSystem', () => {
   });
 });
 
+describe('the reach of a played row (#109)', () => {
+  /** A sprite packed into `Inner`, `Inner` packed into `Outer`, and `Outer` placed in the scene. */
+  function nested() {
+    const f = makeSpriteScene();
+    const arm = place(f, f.spriteId, { x: 0, y: 0 });
+    const inner = new CreateContainerCommand(f.sceneId, [arm]);
+    f.stack.execute(inner);
+    const outer = new CreateContainerCommand(f.sceneId, [inner.objectId]);
+    f.stack.execute(outer);
+    const placing = (findAsset(f.project, outer.assetId) as ContainerAsset).objects[0]!;
+    const armTemplate = (findAsset(f.project, inner.assetId) as ContainerAsset).objects[0]!;
+    return { f, outer, path: `${placing.id}/${armTemplate.id}` };
+  }
+
+  const slideX: [number, AnimationKey['value']][] = [
+    [0, 0],
+    [10, 100],
+  ];
+
+  it('reaches a child two containers deep on each instance of the root on its own', () => {
+    const { f, outer, path } = nested();
+    const second = place(f, outer.assetId, { x: 500, y: 0 });
+    const walk = addAnimation(f, outer.assetId, { fps: 10 });
+    addRow(f, walk, 'x', slideX, path);
+    const { world, frame } = startWorld(f, { animations: true });
+    playAnimation(world.findByObjectId(outer.objectId)!, walk.id);
+    frame(0.1);
+    frame(0.5);
+    const x = (instance: string) => world.findByObjectId(instanceChildId(instance, path))!.x;
+    expect(x(outer.objectId)).toBeCloseTo(50);
+    expect(x(second)).toBe(0);
+  });
+
+  it('reaches into a container placed in a scene, baked for play or resolved for the editor run', () => {
+    for (const bakeContainers of [true, false]) {
+      const { f, outer, path } = nested();
+      const box = place(f, f.spriteId, { x: 0, y: 0 });
+      const id = instanceChildId(outer.objectId, path);
+      const walk = addAnimation(f, f.sceneId, { fps: 10 });
+      addRow(f, walk, 'x', slideX, id);
+      const world = World.instantiate(f.project, f.sceneId, { bakeContainers });
+      world.addSystem(new AnimationSystem());
+      playAnimation(world.findByObjectId(box)!, walk.id);
+      world.tick(0.1);
+      world.tick(0.5);
+      expect(world.findByObjectId(id)!.x).toBeCloseTo(50);
+    }
+  });
+
+  it("plays the scene's own background, and a once-reset pass puts it back", () => {
+    const f = makeSpriteScene();
+    const box = place(f, f.spriteId, { x: 0, y: 0 });
+    f.sceneOf().props.backgroundColor = 0x123456;
+    const walk = addAnimation(f, f.sceneId, { fps: 10, playback: 'once-reset' });
+    addRow(f, walk, 'backgroundColor', [
+      [0, 0x000000],
+      [10, 0xff0000],
+    ]);
+    const { world, frame } = startWorld(f, { animations: true });
+    playAnimation(world.findByObjectId(box)!, walk.id);
+    frame(0.1);
+    frame(0.5);
+    expect(world.backgroundColor).toBe(0x800000);
+    for (let i = 0; i < 10; i++) frame(0.1);
+    expect(world.backgroundColor).toBe(0x123456);
+    expect(f.sceneOf().props.backgroundColor).toBe(0x123456);
+  });
+});
+
 describe('the animation nodes', () => {
   /** A behavior below the sprite plays `walk` on its owner at start and counts `On animation finished`. */
   function listening(filter: 'walk' | 'other') {