feuerwerk/src/editor/particles/ParticlePreview.ts

import { Container, Graphics, Texture } from 'pixi.js';
import type { ParticlesAsset } from '../../core/model/Asset';
import { translation } from '../../core/model/matrix';
import type { PropertyBag } from '../../core/model/Properties';
import { resolveTexture } from '../../core/model/texture';
import { defaultsFor } from '../../core/properties/PropertySchema';
import { SHEET_EDGE } from '../../core/shader/nodes';
import { crisp, hairline, type Size, Theme, Widget } from '../../ui';
import { ParticleField } from '../../viewport/particles';
import { particleLibrary } from '../../viewport/ParticleLibrary';
import { shaderLibrary } from '../../viewport/ShaderLibrary';
import { textureLibrary } from '../../viewport/TextureLibrary';
import type { EditorState } from '../state';

const MIN_HEIGHT = 40;

/**
 * The asset's own particles, emitted from the middle of the panel by a source that wears the asset's
 * own rows. It is the one place a formula graph can be judged: the numbers say nothing. What it is
 * not is an instance – a source placed in a scene may override every one of those rows, and the tab
 * has no way to know which of them is meant.
 */
export class ParticlePreview extends Widget {
  private readonly bg = crisp(new Graphics());
  private readonly content = new Container();
  private readonly clip = new Graphics();
  private readonly field = new ParticleField();
  private asset: ParticlesAsset | null = null;
  /** Null: the preview runs on the library clock. A number: it stands at that second. */
  private held: number | null = null;

  constructor(private readonly state: EditorState) {
    super();
    this.minHeight = MIN_HEIGHT;
    this.content.addChild(this.field.container);
    this.content.mask = this.clip;
    this.addChild(this.bg, this.content, this.clip);
  }

  override measure(): Size {
    return { w: Math.max(this.minWidth, 100), h: Math.max(this.minHeight, MIN_HEIGHT) };
  }

  show(asset: ParticlesAsset | null): void {
    this.asset = asset;
    this.invalidate();
  }

  /** Seconds the shown source has been emitting, whether held or running. */
  get time(): number {
    return this.held ?? Math.max(0, this.field.elapsed(particleLibrary.now()));
  }

  get holding(): boolean {
    return this.held !== null;
  }

  hold(at: number | null): void {
    // Letting go has to move the origin, not just stop faking one: the library clock keeps counting
    // under a freeze, so the panel would otherwise resume at the second it would have reached.
    if (at === null && this.held !== null) this.field.rebase(particleLibrary.now(), this.held);
    this.held = at;
    this.invalidate();
  }

  /** Back to second 0 – a held panel stands there too, rather than keeping the second it was on. */
  restart(): void {
    this.field.restart(particleLibrary.now());
    if (this.held !== null) this.held = 0;
    this.invalidate();
  }

  /** How many particles the preview is drawing – what the checks read. */
  get count(): number {
    return this.field.count;
  }

  override redraw(): void {
    const c = Theme.colors;
    // A ground of its own and a rule along the top: on the graph's own background the strip was
    // invisible as a thing, and a particle standing still read as a node that had lost its box.
    this.bg.clear().rect(0, 0, this.w, this.h).fill(c.panel);
    this.bg.rect(0, 0, this.w, hairline()).fill(c.border);
    this.clip.clear().rect(0, 0, this.w, this.h).fill(0xffffff);
    this.field.container.visible = this.asset !== null;
    if (!this.asset) return;
    const build = particleLibrary.buildFor(this.asset);
    const rows = build.compiled?.params ?? [];
    const props = previewProps(this.asset, rows);
    const params = rows.map((row) => Number(props[row.key] ?? row.default));
    const ref = resolveTexture(this.state.project, props);
    const texture = ref ? textureLibrary.get(ref, SHEET_EDGE) : null;
    // The source sits in the middle of the panel; a fountain then has room above and below it.
    const m = translation(this.w / 2, this.h / 2);
    this.field.hold(this.held);
    this.field.wear(props, shaderLibrary.source(this.state.project));
    this.field.sync(build.compiled, props, params, m, texture ?? Texture.WHITE, particleLibrary.now());
  }

  override destroy(): void {
    this.field.destroy();
    super.destroy();
  }
}

/**
 * A source as the asset alone describes it: the rows the asset carries, over the type's defaults for
 * the ones it does not, with the graph's own parameters at their declared defaults underneath.
 */
function previewProps(
  asset: ParticlesAsset,
  params: readonly { key: string; default: number }[],
): PropertyBag {
  const props = defaultsFor('particles');
  for (const row of params) props[row.key] = row.default;
  return { ...props, ...asset.props };
}