feuerwerk/src/core/model/animationPreview.ts

/**
 * What the Animation tab shows above the timeline (#99): the root asset with every row's value at
 * 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 {
  animatableDefs,
  animatedDefOf,
  frameCount,
  isPositionRow,
  PLACED_ROOT_ID,
  placedRoot,
  playbackOf,
  trackWriteAt,
} from './animation';
import type { AnimationAsset, AnimationTrack, Asset } from './Asset';
import { type CurveLookup, curveLookup } from './curve';
import { instanceChildId, objectRef } from './instance';
import { findAsset, type ObjectHolder, type Project } from './Project';
import { resolveSceneObjectProps } from '../properties/resolve';

/**
 * 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. 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.
 * `reverse` is ping-pong's way back, as `playheadAt` reports it.
 */
export function previewHolder(
  project: Project,
  animation: AnimationAsset,
  frame: number,
  reverse = false,
): ObjectHolder | undefined {
  const root = findAsset(project, animation.root);
  if (!root) return undefined;
  const reset = playbackOf(animation) === 'once-reset' && frame >= frameCount(animation);
  const holder = root.type === 'scene' ? sceneCopy(root) : placedHolder(root);
  const at: ReadAt = { frame, reverse, curves: curveLookup(project) };
  for (const track of reset ? [] : animation.tracks) {
    if (root.type === 'scene' && track.target === '') writeScene(holder, track, at);
    else writeObject(project, holder, previewObjectId(root, track.target), track, at);
  }
  return holder;
}

/** The id the preview draws a row's target under – for a check that wants to look at it. */
export function previewObjectId(root: Asset | undefined, target: string): string {
  if (root?.type === 'scene') return target;
  return target === '' ? PLACED_ROOT_ID : instanceChildId(PLACED_ROOT_ID, target);
}

/** 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 placedHolder(root: Asset): ObjectHolder {
  return { id: PLACED_ROOT_ID, type: 'container', name: root.name, props: {}, objects: [placedRoot(root)] };
}

/** Where on the timeline a row is read, and the Curve assets its keys may blend along. */
interface ReadAt {
  frame: number;
  reverse: boolean;
  curves: CurveLookup;
}

/** A row on the scene itself: its value goes into the copy's own properties. */
function writeScene(holder: ObjectHolder, track: AnimationTrack, at: ReadAt): void {
  const def = animatableDefs('scene').find((d) => d.key === track.property);
  if (!def) return;
  const base = holder.props[track.property] ?? def.default;
  const value = trackWriteAt(track, def, at.frame, base, at.reverse, at.curves);
  if (value !== undefined) holder.props[track.property] = value;
}

function writeObject(
  project: Project,
  holder: ObjectHolder,
  id: string,
  track: AnimationTrack,
  at: ReadAt,
): void {
  const ref = objectRef(project, holder, id);
  const asset = ref && findAsset(project, ref.object.assetId);
  if (!ref || !asset) return;
  // Resolved, so a shader worn through an override or an instance edit brings its parameters (#104).
  const props = resolveSceneObjectProps(project, asset, ref.object);
  const def = animatedDefOf(project, asset, props, track.property);
  if (!def) return;
  const key = track.property;
  if (isPositionRow(asset.type, key)) {
    const value = trackWriteAt(track, def, at.frame, ref.object.position[key], at.reverse, at.curves);
    if (value !== undefined) ref.setPosition({ ...ref.object.position, [key]: Number(value) });
    return;
  }
  const value = trackWriteAt(track, def, at.frame, props[key], at.reverse, at.curves);
  if (value !== undefined) ref.setOverride(key, value);
}