feuerwerk/src/viewport/WorldViewport.ts

import { Container, type FederatedPointerEvent, Graphics, type Mesh, Texture } from 'pixi.js';
import { isSymbolType } from '../core/model/AssetTypes';
import { type Extent, scaleOf } from '../core/model/matrix';
import type { Vec2 } from '../core/model/Properties';
import { footprintExtent, footprintOf, placementOf } from '../core/properties/bounds';
import { cameraFrame, rectsIntersect, type WorldRect } from '../core/properties/camera';
import type { ClipRegion } from '../core/properties/clip';
import type { Project } from '../core/model/Project';
import { type Size, ui, Widget } from '../ui';
import { fontLibrary } from './FontLibrary';
import { drawSlots } from './drawOrder';
import type { DrawItem } from './items';
import { hashId } from '../core/particles/nodes';
import { ParticleField } from './particles';
import { particleLibrary } from './ParticleLibrary';
import { SHEET_EDGE } from '../core/shader/nodes';
import { shaderLibrary } from './ShaderLibrary';
import { type ShaderSource, wornShader } from './shaders';
import { disposeSpriteMesh, drawItem, newSpriteMesh, syncSpriteMesh } from './symbols';
import { TextPicture } from './textPicture';
import { cellCentre, type LayerFocus, TilemapField } from './tilemap';
import { textureLibrary } from './TextureLibrary';
import { gameClock } from '../core/time';
import { overlayView, type View, worldBounds, worldToScreen } from './view';
import type { ActiveCamera } from './activeCamera';
import { CameraShade } from './cameraShade';
import { cameraSees } from '../core/model/renderLayers';

/** How strongly the cut-off part of an object shows while the scene view opens its clip area (#260). */
const CLIP_GHOST_ALPHA = 0.3;

/**
 * What a view draws from: the project and word of when it changed. The editor's state is one; a
 * released game (#266), which has no editor, hands over its own.
 */
export interface ViewSource {
  readonly project: Project;
  on(event: 'project' | 'selection' | 'mode' | 'runtime', listener: () => void): unknown;
}

export interface Frame {
  items: DrawItem[];
  background: number;
}

export abstract class WorldViewport<S extends ViewSource = ViewSource> extends Widget {
  protected readonly bg = new Graphics();
  protected readonly content = new Container();
  protected readonly world = new Container();
  /** Masks and objects: what a camera's shader is laid over (#299), drawn into its picture first. */
  private readonly shaded = new Container();
  /** Where `shaded` waits while the shader's picture stands in for it: on no stage at all. */
  private readonly offstage = new Container();
  private cameraShade: CameraShade | null = null;
  /** Ordered by `z`, ties by hierarchy order (see `syncDrawOrder`). */
  protected readonly objects = new Container();
  /** Editor symbols, always above `objects` so no sprite can hide them whatever the z-order. */
  protected readonly overlay = new Container();
  protected readonly contentMask = new Graphics();
  protected readonly nodes = new Map<string, Graphics>();
  /** Text content of text items: a sibling of the item's node, kept next to it in z. */
  private readonly texts = new Map<string, TextPicture>();
  /** Pictures of sprite items: siblings as well, each right under its node. */
  private readonly sprites = new Map<string, Mesh>();
  /** The drawn particles of each source, one container – and one draw call – per source. */
  private readonly fields = new Map<string, ParticleField>();
  /** The meshes of each placed tilemap, one container per layer (#174). */
  private readonly tilemaps = new Map<string, TilemapField>();
  /**
   * What clip areas cut off (#260), as a mask per drawn thing: Pixi lets a mask serve only one, and
   * switches a shared one back on as content once any of them lets go of it.
   */
  private readonly masks = new Container();
  private readonly maskOf = new Map<Container, Graphics>();
  /** The cut-off part of a sprite or text, drawn faintly under it while its clip area is open. */
  private readonly ghostSprites = new Map<string, Mesh>();
  private readonly ghostTexts = new Map<string, TextPicture>();
  private visibleCount = 0;
  private animated = false;
  protected lastItems: DrawItem[] = [];
  /**
   * What the last full redraw was drawn for: its zoom and view size, and per object node the box
   * it is culled by (`null`: never culled, a particle source). What `moveCamera` needs to tell
   * whether a pan changes anything but where the world sits.
   */
  private drawn: {
    scale: number;
    w: number;
    h: number;
    culled: { node: Graphics; extent: Extent | null }[];
  } | null = null;
  /** Full redraws and camera-only moves since start (test hook). */
  private redraws = 0;
  private cameraMoves = 0;
  private readonly stopFiles: (() => void)[];
  /** One view per overlay camera (#302), by camera id, laid over this one in camera order. */
  private readonly overlays = new Map<string, OverlayCameraView>();

  protected constructor(protected readonly state: S) {
    super();
    this.shaded.addChild(this.masks, this.objects);
    this.world.addChild(this.shaded, this.overlay);
    this.content.addChild(this.world);
    this.addChild(this.bg, this.content, this.contentMask);
    this.content.mask = this.contentMask;
    this.cursor = 'default';

    state.on('project', () => this.redraw());
    state.on('selection', () => this.redraw());
    state.on('mode', () => this.redraw());
    // While a Time shader is on screen the ticker redraws every frame anyway (`animate`).
    state.on('runtime', () => {
      if (this.visible && !this.animated) this.redraw();
    });
    // Unconditional: a picture or a typeface arriving fires once per file, not per frame.
    this.stopFiles = [
      textureLibrary.onChange(() => this.redraw()),
      fontLibrary.onChange(() => this.redraw()),
    ];
  }

  /** The libraries outlive a signed-out editor; a stale listener would redraw destroyed graphics. */
  override destroy(options?: Parameters<Widget['destroy']>[0]): void {
    for (const stop of this.stopFiles) stop();
    for (const overlay of this.overlays.values()) overlay.destroy();
    this.unshadeCamera();
    this.offstage.destroy();
    super.destroy(options);
  }

  override measure(): Size {
    return { w: Math.max(this.minWidth, 200), h: Math.max(this.minHeight, 200) };
  }

  protected abstract currentView(): View | null;

  /** The camera the view is through, whose `Sees` decides what is drawn (#302); none in the scene view. */
  protected mainCamera(): ActiveCamera | null {
    return null;
  }

  /** The overlay cameras laid over the main one (#302), in the order they are laid on. */
  protected overlayCameras(): ActiveCamera[] {
    return [];
  }

  /** The camera whose shader is laid over this view (#299): the one the view is through. */
  protected shadingCamera(main: ActiveCamera | null, _items: DrawItem[]): ActiveCamera | null {
    return main;
  }

  /** Whether the world stays drawn around the shaded frame: the scene view shows more than the camera. */
  protected keepsWorldAroundShader(): boolean {
    return false;
  }

  /** Only called when `currentView()` is non-null. */
  protected abstract collectFrame(): Frame;

  /** Fills the whole widget, behind and around the view rectangle. */
  protected abstract get baseColor(): number;

  protected paintsBackground(): boolean {
    return true;
  }

  protected get itemsInteractive(): boolean {
    return false;
  }

  protected beforeItems(_view: View | null): void {}

  protected afterItems(_items: DrawItem[], _view: View): void {}

  /** `extent` is the world rectangle around the item as drawn, turn and size included. */
  protected syncDecorations(_item: DrawItem, _onScreen: boolean, _scale: number, _extent: Extent): void {}

  /** An item disappeared: drop whatever `syncDecorations` created for it. */
  protected disposeDecorations(_id: string): void {}

  /** Whether the item's own drawing is switched off – it is then neither seen nor hit. */
  protected hidesShape(_item: DrawItem): boolean {
    return false;
  }

  protected onItemPointerDown(_objectId: string, _e: FederatedPointerEvent): void {}

  /** Whether the part a clip area cuts off the item is shown faintly and can be grabbed (#260). */
  protected opensClip(_item: DrawItem): boolean {
    return false;
  }

  /** Whether the object itself is selected – a selected collider shows its area filled. */
  protected isSelected(_objectId: string): boolean {
    return false;
  }

  /** Screen-space drawing that follows the camera, redrawn after a full redraw and after a pan. */
  protected drawOnScreen(_items: DrawItem[], _view: View): void {}

  debugInfo(): { rendering: boolean; visibleItems: number; redraws: number; cameraMoves: number } {
    return {
      rendering: this.currentView() !== null,
      visibleItems: this.visibleCount,
      redraws: this.redraws,
      cameraMoves: this.cameraMoves,
    };
  }

  /**
   * The camera moved and nothing else did – a pan. Zoom and size are the same, so every node is
   * drawn as it was; only the world's position and the screen-space overlays follow. Anything
   * else, or an object crossing the edge of the view, takes the full redraw, which would collect,
   * redraw and re-upload every shape of a pan frame for nothing.
   */
  protected moveCamera(): void {
    const view = this.currentView();
    const drawn = this.drawn;
    if (!view || !drawn || view.scale !== drawn.scale || view.rect.w !== drawn.w || view.rect.h !== drawn.h) {
      this.redraw();
      return;
    }
    const bounds = worldBounds(view);
    for (const { node, extent } of drawn.culled)
      if ((extent === null || rectsIntersect(extent, bounds)) !== node.visible) {
        this.redraw();
        return;
      }
    this.cameraMoves++;
    this.placeWorld(view);
    this.drawOnScreen(this.lastItems, view);
  }

  private placeWorld(view: View): void {
    const { rect } = view;
    this.world.position.set(
      rect.x + rect.w / 2 - view.x * view.scale,
      rect.y + rect.h / 2 - view.y * view.scale,
    );
    this.world.scale.set(view.scale);
  }

  /**
   * The particles of one source as drawn, in world units, oldest first – what a check reads instead
   * of guessing from pixels. `limit` keeps a stream of 500 from becoming 500 lines of JSON.
   */
  particleInfo(
    objectId: string,
    limit = 8,
  ): {
    count: number;
    drawn: { x: number; y: number; scaleX: number; alpha: number; tint: number }[];
  } | null {
    const field = this.fields.get(objectId);
    if (!field || !field.node.visible) return null;
    return {
      count: field.count,
      drawn: field.container.particleChildren.slice(0, limit).map((p) => ({
        x: Math.round(p.x * 100) / 100,
        y: Math.round(p.y * 100) / 100,
        scaleX: Math.round(p.scaleX * 1000) / 1000,
        alpha: Math.round(p.alpha * 1000) / 1000,
        tint: p.tint,
      })),
    };
  }

  /**
   * Starts every source's clock over at `now`. With particle time frozen this is what makes a
   * measurement exact: freeze, restart, move the clock to the second wanted, read.
   */
  restartParticles(now: number): void {
    for (const field of this.fields.values()) field.restart(now);
    this.redraw();
  }

  /** True after a redraw that drew a sprite wearing a Time shader: the picture moves by itself. */
  get animates(): boolean {
    return this.animated;
  }

  /** How often the view was drawn so far; `animate` is told the count its tick began with. */
  get redrawCount(): number {
    return this.redraws;
  }

  /**
   * Called every tick: redraws while the last redraw found a Time shader on screen. A view drawn
   * since the tick began, at `drawnBefore`, already shows this frame – a run draws its views
   * itself, and drawing them again cost a second collect of the whole world each frame (#284).
   */
  animate(drawnBefore: number): void {
    if (this.visible && this.animated && this.redraws === drawnBefore) this.redraw();
  }

  layerOf(objectId: string): 'objects' | 'overlay' | null {
    const node = this.nodes.get(objectId);
    if (!node) return null;
    return node.parent === this.overlay ? 'overlay' : 'objects';
  }

  /** Ids in the order they are drawn, back to front. */
  drawOrder(): string[] {
    return this.objects.children.filter((node) => node.visible).map((node) => node.label);
  }

  /** Where an object is drawn, in global screen coordinates. */
  objectScreen(objectId: string): Vec2 | null {
    const view = this.currentView();
    const item = this.lastItems.find((i) => i.id === objectId);
    if (!item || !view) return null;
    const local = worldToScreen(view, item.x, item.y);
    const origin = this.getGlobalPosition();
    return { x: origin.x + local.x, y: origin.y + local.y };
  }

  /**
   * The screen rectangle around an object, so tests can sample the pixels inside it: centre plus
   * size, and for a turned object the box around its corners.
   */
  objectRect(objectId: string): { x: number; y: number; w: number; h: number } | null {
    const view = this.currentView();
    const item = this.lastItems.find((i) => i.id === objectId);
    if (!item || !view) return null;
    const extent = footprintExtent(item.type, item.props, item.m, item.frame);
    const local = worldToScreen(view, (extent.left + extent.right) / 2, (extent.top + extent.bottom) / 2);
    const origin = this.getGlobalPosition();
    return {
      x: origin.x + local.x,
      y: origin.y + local.y,
      w: (extent.right - extent.left) * view.scale,
      h: (extent.bottom - extent.top) * view.scale,
    };
  }

  override redraw(): void {
    const view = this.currentView();
    this.bg.clear().rect(0, 0, this.w, this.h).fill(this.baseColor);
    this.beforeItems(view);
    this.contentMask.clear();
    this.content.visible = view !== null;
    this.visibleCount = 0;
    this.animated = false;
    this.drawn = null;
    if (!view) {
      this.unshadeCamera();
      this.syncOverlays(null, null, null);
      return;
    }

    this.redraws++;
    const frame = this.collectFrame();
    const { background } = frame;
    const camera = this.mainCamera();
    const items = camera ? seenBy(camera, frame.items) : frame.items;
    this.lastItems = items;
    const { rect } = view;
    if (this.paintsBackground()) this.bg.rect(rect.x, rect.y, rect.w, rect.h).fill(background);
    this.contentMask.rect(rect.x, rect.y, rect.w, rect.h).fill(0xffffff);

    this.placeWorld(view);
    const bounds = worldBounds(view);
    const shaders = shaderLibrary.source(this.state.project);
    const culled: { node: Graphics; extent: Extent | null }[] = [];

    const seen = new Set<string>();
    for (const item of items) {
      seen.add(item.id);
      const size = footprintOf(item.type, item.props, item.frame);
      const extent = footprintExtent(item.type, item.props, item.m, item.frame);
      // A switched-off object is not drawn at all, in the scene view as in the game; it is
      // selected and switched back on from the hierarchy panel. A source is never culled by its
      // own little square: its particles may be anywhere on screen while it is not. Nor is a wearer
      // of a shader that pads it (#69) or moves its corners (#79): both draw past its rectangle.
      const worn = wornShader(item.props, shaders);
      const unbound = item.type === 'particles' || (worn?.padding ?? 0) > 0 || Boolean(worn?.vertex);
      const onScreen = item.enabled && (unbound || rectsIntersect(extent, bounds));
      let node = this.nodes.get(item.id);
      if (!node) {
        node = new Graphics();
        node.label = item.id;
        node.cursor = 'move';
        node.on('pointerdown', (e: FederatedPointerEvent) => this.onItemPointerDown(item.id, e));
        this.nodes.set(item.id, node);
        (isSymbolType(item.type) ? this.overlay : this.objects).addChild(node);
      }
      const hidden = this.hidesShape(item);
      node.visible = onScreen && !hidden;
      if (item.enabled && !hidden) culled.push({ node, extent: unbound ? null : extent });
      node.eventMode = this.itemsInteractive && node.visible ? 'static' : 'none';
      this.syncDecorations(item, onScreen, view.scale, extent);
      this.syncText(item, onScreen, view.scale, shaders);
      this.syncSprite(item, onScreen, size, shaders);
      this.syncParticles(item, onScreen, shaders, view, bounds);
      this.syncTilemap(item, onScreen);
      if (!onScreen) continue;
      this.visibleCount++;
      if (hidden) continue;
      drawItem(
        node,
        item,
        size,
        view.scale * scaleOf(placementOf(item.type, item.m)),
        this.isSelected(item.id),
      );
    }
    this.afterItems(items, view);
    this.drawOnScreen(items, view);
    this.drawn = { scale: view.scale, w: rect.w, h: rect.h, culled };
    for (const [id, node] of this.nodes) {
      if (seen.has(id)) continue;
      this.texts.get(id)?.destroy();
      this.texts.delete(id);
      const sprite = this.sprites.get(id);
      if (sprite) disposeSpriteMesh(sprite);
      this.sprites.delete(id);
      this.fields.get(id)?.destroy();
      this.fields.delete(id);
      this.tilemaps.get(id)?.destroy();
      this.tilemaps.delete(id);
      this.dropGhosts(id);
      node.destroy();
      this.nodes.delete(id);
      this.disposeDecorations(id);
    }
    this.syncDrawOrder(items);
    this.sweepMasks();
    this.shadeCamera(this.shadingCamera(camera, items), view, shaders, background);
    this.syncOverlays(frame, view, camera);
  }

  /**
   * Lays the camera's shader over its frame (#299): the masks and objects are drawn into the
   * camera's picture, cleared to the scene's background – see-through on a view that paints none –
   * and the picture stands in for them. Without a shader that compiles they are drawn as they are.
   */
  private shadeCamera(
    camera: ActiveCamera | null,
    view: View,
    shaders: ShaderSource,
    background: number,
  ): void {
    const renderer = ui().app.renderer;
    const shade = this.cameraShade ?? new CameraShade();
    const clear = this.paintsBackground() ? background : null;
    const ppu = view.scale * renderer.resolution;
    const mesh = camera ? shade.draw(this.shaded, camera, shaders, ppu, renderer, clear) : null;
    if (!camera || !mesh) {
      if (shade !== this.cameraShade) shade.destroy();
      this.unshadeCamera();
      return;
    }
    this.cameraShade = shade;
    if (!this.keepsWorldAroundShader() && this.shaded.parent !== this.offstage)
      this.offstage.addChild(this.shaded);
    if (mesh.parent !== this.world) this.world.addChildAt(mesh, this.world.getChildIndex(this.overlay));
    if (wornShader(camera.props, shaders)?.time) this.animated = true;
  }

  /** Back to drawing the objects themselves. */
  private unshadeCamera(): void {
    if (!this.cameraShade) return;
    this.cameraShade.destroy();
    this.cameraShade = null;
    if (this.shaded.parent !== this.world)
      this.world.addChildAt(this.shaded, this.world.getChildIndex(this.overlay));
  }

  /** The pixels of the camera shader's picture while one is drawn (#299, test hook). */
  cameraShaderPixels(): { w: number; h: number } | null {
    return this.cameraShade?.pixels ?? null;
  }

  /**
   * Lays one view per overlay camera over this one (#302): each draws what its camera sees of the
   * same frame, see-through, fitted into the main picture. Without a main view there are none.
   */
  private syncOverlays(frame: Frame | null, main: View | null, camera: ActiveCamera | null): void {
    const cameras = frame && main && camera ? this.overlayCameras() : [];
    const wanted = new Set(cameras.map((c) => c.id));
    for (const [id, overlay] of this.overlays)
      if (!wanted.has(id)) {
        overlay.destroy();
        this.overlays.delete(id);
      }
    let at = this.getChildIndex(this.contentMask) + 1;
    for (const overlayCamera of cameras) {
      let overlay = this.overlays.get(overlayCamera.id);
      if (!overlay) {
        overlay = new OverlayCameraView(() => this.state.project);
        this.overlays.set(overlayCamera.id, overlay);
        this.addChild(overlay);
      }
      this.setChildIndex(overlay, at++);
      const view = overlayView(overlayCamera, main!, cameraFrame(camera!.props));
      overlay.show(overlayCamera, view, frame!, this.w, this.h);
      if (overlay.animates) this.animated = true;
    }
  }

  /** What each overlay camera draws, in the order they are laid on (#302, test hook). */
  overlayInfo(): { camera: string; drawOrder: string[]; rect: View['rect'] }[] {
    return [...this.overlays].map(([camera, overlay]) => ({
      camera,
      drawOrder: overlay.drawOrder(),
      rect: overlay.shownRect(),
    }));
  }

  /**
   * Re-attaches the object nodes in ascending `z`, ties in hierarchy order, each layer of a map
   * sorted in on its own (#174, see `drawSlots`). Explicit rather than Pixi's lazy
   * `sortableChildren` so the order is deterministic and honours hierarchy changes.
   */
  private syncDrawOrder(items: DrawItem[]): void {
    this.objects.removeChildren();
    const byId = new Map(items.map((item) => [item.id, item]));
    for (const { id, layerId, row } of drawSlots(items)) {
      const clip = byId.get(id)?.clip ?? null;
      if (layerId) {
        const layer = this.tilemaps.get(id)?.layerContainer(layerId, row);
        if (layer) this.objects.addChild(this.clipTo(layer, clip));
        continue;
      }
      // Picture and text are siblings because Graphics may not have children: the picture right
      // under its node, which only holds the hit area, the text right above its box. A ghost goes
      // right under what it is the rest of.
      const ghost = this.ghostSprites.get(id);
      if (ghost) this.objects.addChild(this.clipTo(ghost, clip, true));
      const sprite = this.sprites.get(id);
      if (sprite) this.objects.addChild(this.clipTo(sprite, clip));
      const node = this.nodes.get(id);
      if (node) this.objects.addChild(node);
      const ghostText = this.ghostTexts.get(id);
      if (ghostText) this.objects.addChild(this.clipTo(ghostText.mesh, clip, true));
      const text = this.texts.get(id);
      if (text) this.objects.addChild(this.clipTo(text.mesh, clip));
      const field = this.fields.get(id);
      if (field) this.objects.addChild(this.clipTo(field.node, clip));
    }
  }

  /**
   * Cuts `target` to the region, or with `inverse` to everything outside it. The mask lives in
   * world units like the objects, and stays with the target until the target goes.
   */
  private clipTo<T extends Container>(target: T, region: ClipRegion | null, inverse = false): T {
    let mask = this.maskOf.get(target);
    if (!region) {
      if (mask) {
        target.mask = null;
        mask.destroy();
        this.maskOf.delete(target);
      }
      return target;
    }
    if (!mask) {
      mask = new Graphics();
      this.masks.addChild(mask);
      this.maskOf.set(target, mask);
      target.setMask({ mask, inverse });
    }
    mask.clear();
    if (region.length >= 3) mask.poly([...region]).fill(0xffffff);
    return target;
  }

  /** Masks whose target is gone: a tilemap drops the containers of layers it no longer has itself. */
  private sweepMasks(): void {
    for (const [target, mask] of this.maskOf)
      if (target.destroyed) {
        mask.destroy();
        this.maskOf.delete(target);
      }
  }

  private dropGhosts(id: string): void {
    const sprite = this.ghostSprites.get(id);
    if (sprite) disposeSpriteMesh(sprite);
    this.ghostSprites.delete(id);
    this.ghostTexts.get(id)?.destroy();
    this.ghostTexts.delete(id);
  }

  /** Whether the item has a cut-off part to show faintly right now. */
  private ghosted(item: DrawItem, onScreen: boolean): boolean {
    return onScreen && item.clip !== null && this.opensClip(item);
  }

  /**
   * The particles of one source. Their positions are world units, like everything else under
   * `objects`, so the container itself carries no transform: the source's own goes into each
   * particle, which is what lets one stay where it was born while its source flies on.
   */
  private syncParticles(
    item: DrawItem,
    onScreen: boolean,
    shaders: ShaderSource,
    view: View,
    bounds: WorldRect,
  ): void {
    let field = this.fields.get(item.id);
    if (item.type !== 'particles' || !item.particles || !onScreen) {
      if (field) field.node.visible = false;
      return;
    }
    if (!field) {
      field = new ParticleField();
      this.fields.set(item.id, field);
      this.objects.addChild(field.node);
    }
    field.node.visible = true;
    // A source is a moving picture by definition, so the view keeps redrawing while one is on screen.
    this.animated = true;
    const build = particleLibrary.buildFor(item.particles);
    const compiled = build.compiled;
    const params = compiled ? compiled.params.map((row) => Number(item.props[row.key] ?? row.default)) : [];
    const edge = wornShader(item.props, shaders)?.edge ?? SHEET_EDGE;
    const texture = item.texture ? textureLibrary.get(item.texture, edge) : null;
    field.wear(item.props, shaders, texture);
    field.sync(
      compiled,
      item.props,
      params,
      item.m,
      texture ?? Texture.WHITE,
      particleLibrary.now(),
      item.emits,
      hashId(item.id),
    );
    const renderer = ui().app.renderer;
    field.shadeField(item.props, shaders, item.m, view.scale * renderer.resolution, renderer, bounds);
  }

  /** The device pixels of a source's field-shader picture while one is drawn (#170, test hook). */
  fieldPixels(objectId: string): { w: number; h: number } | null {
    const field = this.fields.get(objectId);
    return field?.node.visible ? field.fieldPixels : null;
  }

  /**
   * A painted map, drawn from its own meshes. It keeps redrawing the view while an animated
   * tile is on it, the same way a Time shader does.
   */
  private syncTilemap(item: DrawItem, onScreen: boolean): void {
    let field = this.tilemaps.get(item.id);
    if (item.type !== 'tilemap' || !item.tilemap || !onScreen) {
      if (field) field.visible = false;
      return;
    }
    if (!field) {
      // Its layers are attached by `syncDrawOrder`, which runs after every item is synced.
      field = new TilemapField();
      this.tilemaps.set(item.id, field);
    }
    field.visible = true;
    field.sync(item, textureLibrary, gameClock.now, this.tilemapFocus(item));
    if (field.animated) this.animated = true;
  }

  /**
   * Which layer of a tilemap is singled out and how (#138). The game view shows every map as the
   * game does; only the scene view, where one paints, has a say.
   */
  protected tilemapFocus(_item: DrawItem): LayerFocus | null {
    return null;
  }

  /** Where the centre of one cell of a placed tilemap is on screen, so a check can sample it. */
  cellScreen(objectId: string, x: number, y: number): Vec2 | null {
    const view = this.currentView();
    const item = this.lastItems.find((i) => i.id === objectId);
    if (!view || !item || item.type !== 'tilemap') return null;
    const centre = cellCentre(item, x, y);
    const local = worldToScreen(view, centre.x, centre.y);
    const origin = this.getGlobalPosition();
    return { x: origin.x + local.x, y: origin.y + local.y };
  }

  /**
   * What a placed tilemap drew last redraw: how many meshes, and how many cells in them; `builds`
   * counts the geometries built since the map came on screen (test hook).
   */
  tilemapInfo(objectId: string): { drawCalls: number; builds: number; tiles: number; layers: number } | null {
    const field = this.tilemaps.get(objectId);
    const item = this.lastItems.find((i) => i.id === objectId);
    if (!field?.visible || !item?.tilemap) return null;
    return {
      drawCalls: field.drawCalls,
      builds: field.builds,
      tiles: item.tilemap.layers.reduce((sum, layer) => sum + layer.tiles.length, 0),
      layers: item.tilemap.layers.length,
    };
  }

  private syncSprite(item: DrawItem, onScreen: boolean, size: Size, shaders: ShaderSource): void {
    let sprite = this.sprites.get(item.id);
    if (item.type !== 'sprite' || !onScreen) {
      if (sprite) sprite.visible = false;
      const ghost = this.ghostSprites.get(item.id);
      if (ghost) disposeSpriteMesh(ghost);
      this.ghostSprites.delete(item.id);
      return;
    }
    if (!sprite) {
      sprite = newSpriteMesh();
      this.sprites.set(item.id, sprite);
      this.objects.addChild(sprite);
    }
    sprite.visible = true;
    if (wornShader(item.props, shaders)?.time) this.animated = true;
    syncSpriteMesh(sprite, item, size, textureLibrary, shaders);
    let ghost = this.ghostSprites.get(item.id);
    if (!this.ghosted(item, onScreen)) {
      if (ghost) disposeSpriteMesh(ghost);
      this.ghostSprites.delete(item.id);
      return;
    }
    if (!ghost) {
      ghost = newSpriteMesh();
      ghost.alpha = CLIP_GHOST_ALPHA;
      this.ghostSprites.set(item.id, ghost);
    }
    syncSpriteMesh(ghost, item, size, textureLibrary, shaders);
  }

  /**
   * The typeface a text is drawn in and how wide that makes it. Both are what a font asset is
   * for, and both arrive asynchronously, so a test cannot read them off the model.
   */
  textInfo(id: string): ReturnType<TextPicture['info']> | null {
    const text = this.texts.get(id);
    return text?.mesh.visible ? text.info() : null;
  }

  private syncText(item: DrawItem, onScreen: boolean, scale: number, shaders: ShaderSource): void {
    let text = this.texts.get(item.id);
    if (item.type !== 'text' || !onScreen) {
      if (text) text.mesh.visible = false;
      this.ghostTexts.get(item.id)?.destroy();
      this.ghostTexts.delete(item.id);
      return;
    }
    if (!text) {
      text = new TextPicture();
      this.texts.set(item.id, text);
      this.objects.addChild(text.mesh);
    }
    text.mesh.visible = true;
    if (wornShader(item.props, shaders)?.time) this.animated = true;
    text.sync(item, scale, shaders);
    let ghost = this.ghostTexts.get(item.id);
    if (!this.ghosted(item, onScreen)) {
      ghost?.destroy();
      this.ghostTexts.delete(item.id);
      return;
    }
    if (!ghost) {
      ghost = new TextPicture();
      ghost.mesh.alpha = CLIP_GHOST_ALPHA;
      this.ghostTexts.set(item.id, ghost);
    }
    ghost.sync(item, scale, shaders);
  }
}

/** Only what a camera sees (#302): the items on the render layers in its `Sees`. */
function seenBy(camera: ActiveCamera, items: DrawItem[]): DrawItem[] {
  return items.filter((item) => cameraSees(camera.props, item.renderLayer));
}

/**
 * What one overlay camera sees (#302), drawn like any view but handed its view and frame by the view
 * it lies on, which also redraws it. See-through, and never hit: the mouse belongs to the main
 * camera's view below (#304).
 */
class OverlayCameraView extends WorldViewport {
  private camera: ActiveCamera | null = null;
  private view: View | null = null;
  private frame: Frame = { items: [], background: 0 };

  constructor(project: () => Project) {
    super({
      get project() {
        return project();
      },
      on: () => undefined,
    });
    this.eventMode = 'none';
    this.bg.visible = false;
  }

  show(camera: ActiveCamera, view: View, frame: Frame, w: number, h: number): void {
    this.camera = camera;
    this.view = view;
    this.frame = frame;
    this.w = w;
    this.h = h;
    this.redraw();
  }

  shownRect(): View['rect'] {
    return this.view?.rect ?? { x: 0, y: 0, w: 0, h: 0 };
  }

  protected override currentView(): View | null {
    return this.view;
  }

  protected override mainCamera(): ActiveCamera | null {
    return this.camera;
  }

  protected override collectFrame(): Frame {
    return this.frame;
  }

  protected override get baseColor(): number {
    return 0;
  }

  protected override paintsBackground(): boolean {
    return false;
  }
}