Tile.ts

/*---------------------------------------------------------------------------------------------
* Copyright (c) 2019 Bentley Systems, Incorporated. All rights reserved.
* Licensed under the MIT License. See LICENSE.md in the project root for license terms.
*--------------------------------------------------------------------------------------------*/
/** @module Tile */

import {
  assert,
  BeTimePoint,
  dispose,
  IDisposable,
} from "@bentley/bentleyjs-core";
import {
  Arc3d,
  ClipPlaneContainment,
  ClipShape,
  ClipMaskXYZRangePlanes,
  ClipVector,
  Point2d,
  Point3d,
  Range3d,
  Transform,
  Vector3d,
  Map4d,
} from "@bentley/geometry-core";
import {
  BoundingSphere,
  ColorDef,
  ElementAlignedBox3d,
  Frustum,
  FrustumPlanes,
  LinePixels,
  TileProps,
} from "@bentley/imodeljs-common";
import { IModelApp } from "../IModelApp";
import { IModelConnection } from "../IModelConnection";
import {
  GraphicBranch,
  RenderClipVolume,
  RenderGraphic,
  RenderMemory,
  RenderPlanarClassifier,
  RenderTextureDrape,
} from "../render/System";
import { GraphicBuilder } from "../render/GraphicBuilder";
import { SceneContext } from "../ViewContext";
import { ViewFrustum } from "../Viewport";
import { TileRequest } from "./TileRequest";
import { TileLoader, TileTree, TraversalSelectionContext, TraversalDetails } from "./TileTree";

const scratchRange2d = [new Point2d(), new Point2d(), new Point2d(), new Point2d()];
function addRangeGraphic(builder: GraphicBuilder, range: Range3d, is2d: boolean): void {
  if (!is2d) {
    builder.addRangeBox(range);
    return;
  }

  // 3d box is useless in 2d and will be clipped by near/far planes anyway
  const pts = scratchRange2d;
  pts[0].set(range.low.x, range.low.y);
  pts[1].set(range.high.x, range.low.y);
  pts[2].set(range.high.x, range.high.y);
  pts[3].set(range.low.x, range.high.y);
  builder.addLineString2d(pts, 0);
}

/** @internal */
export function bisectRange3d(range: Range3d, takeUpper: boolean): void {
  const diag = range.diagonal();
  const pt = takeUpper ? range.high : range.low;
  if (diag.x > diag.y && diag.x > diag.z)
    pt.x = (range.low.x + range.high.x) / 2.0;
  else if (diag.y > diag.z)
    pt.y = (range.low.y + range.high.y) / 2.0;
  else
    pt.z = (range.low.z + range.high.z) / 2.0;
}

/** @internal */
export function bisectRange2d(range: Range3d, takeUpper: boolean): void {
  const diag = range.diagonal();
  const pt = takeUpper ? range.high : range.low;
  if (diag.x > diag.y)
    pt.x = (range.low.x + range.high.x) / 2.0;
  else
    pt.y = (range.low.y + range.high.y) / 2.0;
}

/**
 * Given a Tile, compute the ranges which would result from sub-dividing its range a la IModelTile.getChildrenProps().
 * This function exists strictly for debugging purposes.
 */
function computeChildRanges(tile: Tile): Array<{ range: Range3d, isEmpty: boolean }> {
  const emptyMask = tile.emptySubRangeMask;
  const is2d = tile.root.is2d;
  const bisectRange = is2d ? bisectRange2d : bisectRange3d;

  const ranges: Array<{ range: Range3d, isEmpty: boolean }> = [];
  for (let i = 0; i < 2; i++) {
    for (let j = 0; j < 2; j++) {
      for (let k = 0; k < (is2d ? 1 : 2); k++) {
        const emptyBit = 1 << (i + j * 2 + k * 4);
        const isEmpty = 0 !== (emptyMask & emptyBit);

        const range = tile.range.clone();
        bisectRange(range, 0 === i);
        bisectRange(range, 0 === j);
        if (!is2d)
          bisectRange(range, 0 === k);

        ranges.push({ range, isEmpty });
      }
    }
  }

  return ranges;
}

/** A 3d tile within a [[TileTree]].
 * @internal
 */
export class Tile implements IDisposable, RenderMemory.Consumer {
  public readonly root: TileTree;
  public readonly range: ElementAlignedBox3d;
  public readonly parent: Tile | undefined;
  public readonly depth: number;
  public contentId: string;
  public readonly center: Point3d;
  public readonly radius: number;
  public readonly transformToRoot?: Transform;
  protected _maximumSize: number;
  protected _isLeaf: boolean;
  protected _childrenLastUsed: BeTimePoint;
  protected _childrenLoadStatus: TileTree.LoadStatus;
  protected _children?: Tile[];
  protected _contentRange?: ElementAlignedBox3d;
  protected _graphic?: RenderGraphic;
  protected _rangeGraphic?: RenderGraphic;
  protected _rangeGraphicType: Tile.DebugBoundingBoxes = Tile.DebugBoundingBoxes.None;
  protected _sizeMultiplier?: number;
  protected _request?: TileRequest;
  protected _transformToRoot?: Transform;
  protected _localRange?: ElementAlignedBox3d;
  protected _localContentRange?: ElementAlignedBox3d;
  protected _emptySubRangeMask?: number;
  private _state: TileState;
  private static _loadedRealityChildren = new Array<Tile>();

  public constructor(props: Tile.Params) {
    this.root = props.root;
    this.range = props.range;
    this.parent = props.parent;
    this.depth = undefined !== this.parent ? this.parent.depth + 1 : 0;
    this._state = TileState.NotReady;
    this.contentId = props.contentId;
    this._maximumSize = props.maximumSize;
    this._isLeaf = (true === props.isLeaf);
    this._childrenLastUsed = BeTimePoint.now();
    this._contentRange = props.contentRange;
    this._sizeMultiplier = props.sizeMultiplier;
    if (undefined !== (this.transformToRoot = props.transformToRoot)) {
      this.transformToRoot.multiplyRange(props.range, this.range);
      this._localRange = this.range;
      if (undefined !== props.contentRange) {
        this.transformToRoot.multiplyRange(props.contentRange, this._contentRange);
        this._localContentRange = props.contentRange;
      }
    }
    if (!this.root.loader.tileRequiresLoading(props)) {
      this.setIsReady();    // If no contents, this node is for structure only and no content loading is required.
    }

    this.center = this.range.low.interpolate(0.5, this.range.high);
    this.radius = 0.5 * this.range.low.distance(this.range.high);

    this._childrenLoadStatus = this.hasChildren && this.depth < this.root.loader.maxDepth ? TileTree.LoadStatus.NotLoaded : TileTree.LoadStatus.Loaded;
  }

  public dispose() {
    this._graphic = dispose(this._graphic);
    this._rangeGraphic = dispose(this._rangeGraphic);
    this._rangeGraphicType = Tile.DebugBoundingBoxes.None;

    if (this._children)
      for (const child of this._children)
        dispose(child);

    this._children = undefined;
    this._state = TileState.Abandoned;
  }

  public collectStatistics(stats: RenderMemory.Statistics): void {
    if (undefined !== this._graphic)
      this._graphic.collectStatistics(stats);

    if (undefined !== this._children)
      for (const child of this._children)
        child.collectStatistics(stats);
  }

  public get loadStatus(): Tile.LoadStatus {
    switch (this._state) {
      case TileState.NotReady: {
        if (undefined === this.request)
          return Tile.LoadStatus.NotLoaded;
        else if (TileRequest.State.Loading === this.request.state)
          return Tile.LoadStatus.Loading;

        assert(TileRequest.State.Completed !== this.request.state && TileRequest.State.Failed !== this.request.state); // this.request should be undefined in these cases...
        return Tile.LoadStatus.Queued;
      }
      case TileState.Ready: {
        assert(undefined === this.request);
        return Tile.LoadStatus.Ready;
      }
      case TileState.NotFound: {
        assert(undefined === this.request);
        return Tile.LoadStatus.NotFound;
      }
      default: {
        assert(TileState.Abandoned === this._state);
        return Tile.LoadStatus.Abandoned;
      }
    }
  }

  public get isLoading(): boolean { return Tile.LoadStatus.Loading === this.loadStatus; }
  public get isQueued(): boolean { return Tile.LoadStatus.Queued === this.loadStatus; }
  public get isNotFound(): boolean { return Tile.LoadStatus.NotFound === this.loadStatus; }
  public get isReady(): boolean { return Tile.LoadStatus.Ready === this.loadStatus; }

  public setContent(content: Tile.Content): void {
    // This should never happen but paranoia.
    this._graphic = dispose(this._graphic);

    const { graphic, isLeaf, contentRange, sizeMultiplier } = content;

    this._graphic = graphic;

    // NB: If this tile has no graphics, it may or may not have children - but we don't want to load the children until
    // this tile is too coarse for view based on its size in pixels.
    // That is different than an "undisplayable" tile (maximumSize=0) whose children should be loaded immediately.
    if (undefined !== graphic && 0 === this._maximumSize)
      this._maximumSize = 512;

    if (undefined !== isLeaf && isLeaf !== this._isLeaf) {
      this._isLeaf = isLeaf;
      this.unloadChildren();
    }

    if (undefined !== sizeMultiplier && (undefined === this._sizeMultiplier || sizeMultiplier > this._sizeMultiplier)) {
      this._sizeMultiplier = sizeMultiplier;
      this.contentId = this.loader.adjustContentIdSizeMultiplier(this.contentId, sizeMultiplier);
      if (undefined !== this._children && this._children.length > 1)
        this.unloadChildren();
    }

    if (undefined !== contentRange)
      this._contentRange = contentRange;

    this._emptySubRangeMask = content.emptySubRangeMask;

    this.setIsReady();
  }

  public setIsReady(): void { this._state = TileState.Ready; IModelApp.viewManager.onNewTilesReady(); }
  public setNotFound(): void { this._state = TileState.NotFound; }
  public setAbandoned(): void {
    const children = this.children;
    if (undefined !== children)
      for (const child of children)
        child.setAbandoned();

    this._state = TileState.Abandoned;
  }

  public get maximumSize(): number { return this._maximumSize * this.sizeMultiplier; }
  public get isEmpty(): boolean { return this.isReady && !this.hasGraphics && !this.hasChildren; }
  public get hasChildren(): boolean { return !this.isLeaf; }
  public get contentRange(): ElementAlignedBox3d {
    if (undefined !== this._contentRange)
      return this._contentRange;
    else if (undefined === this.parent && undefined !== this.root.contentRange)
      return this.root.contentRange;
    else
      return this.range;
  }

  public get isLeaf(): boolean { return this._isLeaf; }
  public get isDisplayable(): boolean { return this.maximumSize > 0; }
  public get isParentDisplayable(): boolean { return undefined !== this.parent && this.parent.isDisplayable; }
  public get isUndisplayableRootTile(): boolean { return undefined === this.parent && !this.isDisplayable; }
  public get emptySubRangeMask(): number { return undefined !== this._emptySubRangeMask ? this._emptySubRangeMask : 0; }

  public get graphics(): RenderGraphic | undefined { return this._graphic; }
  public get hasGraphics(): boolean { return undefined !== this.graphics; }
  public get sizeMultiplier(): number { return undefined !== this._sizeMultiplier ? this._sizeMultiplier : 1.0; }
  public get hasSizeMultiplier(): boolean { return undefined !== this._sizeMultiplier; }
  public get children(): Tile[] | undefined { return this._children; }
  public get iModel(): IModelConnection { return this.root.iModel; }
  public get yAxisUp(): boolean { return this.root.yAxisUp; }
  public get loader(): TileLoader { return this.root.loader; }

  public get hasContentRange(): boolean { return undefined !== this._contentRange; }
  public isRegionCulled(args: Tile.DrawArgs): boolean { return Tile._scratchRootSphere.init(this.center, this.radius), this.isCulled(this.range, args, Tile._scratchRootSphere); }
  public isContentCulled(args: Tile.DrawArgs): boolean { return this.isCulled(this.contentRange, args); }

  public getRangeGraphic(context: SceneContext): RenderGraphic | undefined {
    const type = context.viewport.debugBoundingBoxes;
    if (type === this._rangeGraphicType)
      return this._rangeGraphic;

    this._rangeGraphicType = type;
    this._rangeGraphic = dispose(this._rangeGraphic);
    if (Tile.DebugBoundingBoxes.None !== type) {
      const builder = context.createSceneGraphicBuilder();
      if (Tile.DebugBoundingBoxes.Both === type) {
        builder.setSymbology(ColorDef.blue, ColorDef.blue, 1);
        addRangeGraphic(builder, this.range, this.root.is2d);
        if (this.hasContentRange) {
          builder.setSymbology(ColorDef.red, ColorDef.red, 1);
          addRangeGraphic(builder, this.contentRange, this.root.is2d);
        }
      } else if (Tile.DebugBoundingBoxes.ChildVolumes === type) {
        const ranges = computeChildRanges(this);
        for (const range of ranges) {
          const color = range.isEmpty ? ColorDef.blue : ColorDef.green;
          const pixels = !range.isEmpty ? LinePixels.HiddenLine : LinePixels.Solid;
          const width = !range.isEmpty ? 2 : 1;
          builder.setSymbology(color, color, width, pixels);
          addRangeGraphic(builder, range.range, this.root.is2d);
        }
      } else if (Tile.DebugBoundingBoxes.Sphere === type) {
        builder.setSymbology(ColorDef.green, ColorDef.green, 1);

        const x = new Vector3d(this.radius, 0, 0);
        const y = new Vector3d(0, this.radius, 0);
        const z = new Vector3d(0, 0, this.radius);
        builder.addArc(Arc3d.create(this.center, x, y), false, false);
        builder.addArc(Arc3d.create(this.center, x, z), false, false);
        builder.addArc(Arc3d.create(this.center, y, z), false, false);
      } else {
        const color = this.hasSizeMultiplier ? ColorDef.red : (this.isLeaf ? ColorDef.blue : ColorDef.green);
        builder.setSymbology(color, color, 1);
        const range = Tile.DebugBoundingBoxes.Content === type ? this.contentRange : this.range;
        addRangeGraphic(builder, range, this.root.is2d);
      }

      this._rangeGraphic = builder.finish();
    }

    return this._rangeGraphic;
  }

  /** Returns the range of this tile's contents in world coordinates. */
  public computeWorldContentRange(): ElementAlignedBox3d {
    const range = new Range3d();
    if (!this.contentRange.isNull)
      this.root.location.multiplyRange(this.contentRange, range);

    return range;
  }

  public computeVisibility(args: Tile.DrawArgs): Tile.Visibility {
    const forcedDepth = this.root.debugForcedDepth;
    if (undefined !== forcedDepth) {
      if (this.depth === forcedDepth)
        return Tile.Visibility.Visible;
      else
        return Tile.Visibility.TooCoarse;
    }

    // NB: We test for region culling before isDisplayable - otherwise we will never unload children of undisplayed tiles when
    // they are outside frustum
    if (this.isEmpty || this.isRegionCulled(args))
      return Tile.Visibility.OutsideFrustum;

    // some nodes are merely for structure and don't have any geometry
    if (!this.isDisplayable)
      return Tile.Visibility.TooCoarse;

    const hasContentRange = this.hasContentRange;
    if (!this.hasChildren) {
      if (hasContentRange && this.isContentCulled(args))
        return Tile.Visibility.OutsideFrustum;
      else
        return Tile.Visibility.Visible; // it's a leaf node
    }
    const pixelSize = args.getPixelSize(this);
    const maxSize = this.maximumSize * args.tileSizeModifier;

    if (pixelSize > maxSize)
      return Tile.Visibility.TooCoarse;
    else if (hasContentRange && this.isContentCulled(args))
      return Tile.Visibility.OutsideFrustum;
    else
      return Tile.Visibility.Visible;
  }

  public getContentClip(): ClipVector | undefined {
    return ClipVector.createCapture([ClipShape.createBlock(this.contentRange, ClipMaskXYZRangePlanes.All)]);
  }

  protected get _anyChildNotFound() {
    if (this._children !== undefined)
      for (const child of this._children)
        if (child.isNotFound)
          return true;

    return this._childrenLoadStatus === TileTree.LoadStatus.NotFound;
  }

  protected selectRealityChildren(context: TraversalSelectionContext, args: Tile.DrawArgs, traversalDetails: TraversalDetails) {
    const childrenLoadStatus = this.loadChildren(); // NB: asynchronous
    if (TileTree.LoadStatus.Loading === childrenLoadStatus) {
      args.markChildrenLoading();
      this._childrenLastUsed = args.now;
      return;
    }

    if (undefined !== this.children) {
      const traversalChildren = this.root.getTraversalChildren(this.depth);
      traversalChildren.initialize();
      for (let i = 0; i < this.children!.length; i++)
        this.children[i].selectRealityTiles(context, args, traversalChildren.getChildDetail(i));

      traversalChildren.combine(traversalDetails);
    }
  }
  public addBoundingRectangle(builder: GraphicBuilder, color: ColorDef) {
    builder.setSymbology(color, color, 3);
    builder.addRangeBox(this.range);
  }

  public allChildrenIncluded(tiles: Tile[]) {
    if (this.children === undefined || tiles.length !== this.children.length)
      return false;
    for (const tile of tiles)
      if (tile.parent !== this)
        return false;
    return true;
  }
  protected getLoadedRealityChildren(args: Tile.DrawArgs): boolean {
    if (this._childrenLoadStatus !== TileTree.LoadStatus.Loaded || this._children === undefined)
      return false;

    for (const child of this._children) {
      if (child.isReady && Tile.Visibility.Visible === child.computeVisibility(args)) {
        this._childrenLastUsed = args.now;
        Tile._loadedRealityChildren.push(child);
      } else if (!child.getLoadedRealityChildren(args))
        return false;
    }
    return true;
  }

  public selectRealityTiles(context: TraversalSelectionContext, args: Tile.DrawArgs, traversalDetails: TraversalDetails) {
    const vis = this.computeVisibility(args);
    if (Tile.Visibility.OutsideFrustum === vis) {
      this.unloadChildren(args.purgeOlderThan);
      return;
    }

    if (this.isDisplayable && (vis === Tile.Visibility.Visible || this.isLeaf || this._anyChildNotFound)) {
      context.selectOrQueue(this, traversalDetails);
      const preloadSkip = this.root.loader.preloadRealityParentSkip;
      let preloadCount = this.root.loader.preloadRealityParentDepth + preloadSkip;
      let parentDepth = 0;
      for (let parent = this.parent; preloadCount > 0 && parent !== undefined; parent = parent.parent) {
        if (parent.children!.length > 1 && ++parentDepth > preloadSkip) {
          context.preload(parent);
          preloadCount--;
        }

        if (!this.isReady) {      // This tile is visible but not loaded - Use higher resolution children if present
          if (this.getLoadedRealityChildren(args))
            context.select(Tile._loadedRealityChildren);
          Tile._loadedRealityChildren.length = 0;
        }
      }
    } else {
      this.selectRealityChildren(context, args, traversalDetails);
      if (this.isDisplayable) {
        if (0 !== traversalDetails.queuedChildren.length && this.isReady) {
          context.selectOrQueue(this, traversalDetails);
        }
      }
    }
  }

  public selectTiles(selected: Tile[], args: Tile.DrawArgs, numSkipped: number = 0): Tile.SelectParent {
    const vis = this.computeVisibility(args);
    if (Tile.Visibility.OutsideFrustum === vis) {
      this.unloadChildren(args.purgeOlderThan);
      return Tile.SelectParent.No;
    }
    if (Tile.Visibility.Visible === vis) {
      // This tile is of appropriate resolution to draw. If need loading or refinement, enqueue.
      if (!this.isReady) {
        args.insertMissing(this);
      }

      if (this.hasGraphics) {
        // It can be drawn - select it
        ++args.context.viewport.numReadyTiles;
        selected.push(this);
        this.unloadChildren(args.purgeOlderThan);
      } else if (!this.isReady) {
        // It can't be drawn. If direct children are drawable, draw them in this tile's place; otherwise draw the parent.
        // Do not load/request the children for this purpose.
        const initialSize = selected.length;
        const kids = this.children;
        if (undefined === kids)
          return Tile.SelectParent.Yes;

        for (const kid of kids) {
          if (Tile.Visibility.OutsideFrustum !== kid.computeVisibility(args)) {
            if (!kid.hasGraphics) {
              selected.length = initialSize;
              return Tile.SelectParent.Yes;
            } else {
              selected.push(kid);
            }
          }
        }

        this._childrenLastUsed = args.now;
      }

      // We're drawing either this tile, or its direct children.
      return Tile.SelectParent.No;
    }

    // This tile is too coarse to draw. Try to draw something more appropriate.
    // If it is not ready to draw, we may want to skip loading in favor of loading its descendants.
    let canSkipThisTile = this.isReady || this.isParentDisplayable;
    if (canSkipThisTile && this.isDisplayable) { // skipping an undisplayable tile doesn't count toward the maximum
      // Some tiles do not sub-divide - they only facet the same geometry to a higher resolution. We can skip directly to the correct resolution.
      const isNotReady = !this.isReady && !this.hasGraphics && !this.hasSizeMultiplier;
      if (isNotReady) {
        if (numSkipped >= this.root.maxTilesToSkip)
          canSkipThisTile = false;
        else
          numSkipped += 1;
      }
    }

    const childrenLoadStatus = this.loadChildren(); // NB: asynchronous
    const children = canSkipThisTile ? this.children : undefined;
    if (canSkipThisTile && TileTree.LoadStatus.Loading === childrenLoadStatus) {
      args.markChildrenLoading();
      this._childrenLastUsed = args.now;
    }

    if (undefined !== children) {
      // If we are the root tile and we are not displayable, then we want to draw *any* currently available children in our place, or else we would draw nothing.
      // Otherwise, if we want to draw children in our place, we should wait for *all* of them to load, or else we would show missing chunks where not-yet-loaded children belong.
      const isUndisplayableRootTile = this.isUndisplayableRootTile;
      this._childrenLastUsed = args.now;
      let drawChildren = true;
      const initialSize = selected.length;
      for (const child of children) {
        // NB: We must continue iterating children so that they can be requested if missing.
        if (Tile.SelectParent.Yes === child.selectTiles(selected, args, numSkipped)) {
          if (child.loadStatus === Tile.LoadStatus.NotFound) {
            // At least one child we want to draw failed to load. e.g., we reached max depth of map tile tree. Draw parent instead.
            drawChildren = canSkipThisTile = false;
          } else {
            // At least one child we want to draw is not yet loaded. Wait for it to load before drawing it and its siblings, unless we have nothing to draw in their place.
            drawChildren = isUndisplayableRootTile;
          }
        }
      }

      if (drawChildren)
        return Tile.SelectParent.No;

      // Some types of tiles (like maps) allow the ready children to be drawn on top of the parent while other children are not yet loaded.
      if (args.parentsAndChildrenExclusive)
        selected.length = initialSize;
    }

    if (this.isReady) {
      if (this.hasGraphics) {
        selected.push(this);
        if (!canSkipThisTile) {
          // This tile is too coarse, but we require loading it before we can start loading higher-res children.
          ++args.context.viewport.numReadyTiles;
        }
      }

      return Tile.SelectParent.No;
    }

    // This tile is not ready to be drawn. Request it *only* if we cannot skip it.
    if (!canSkipThisTile)
      args.insertMissing(this);

    return this.isParentDisplayable ? Tile.SelectParent.Yes : Tile.SelectParent.No;
  }

  public drawGraphics(args: Tile.DrawArgs): void {
    if (undefined !== this.graphics) {
      args.graphics.add(this.graphics);
      const rangeGraphics = this.getRangeGraphic(args.context);
      if (undefined !== rangeGraphics)
        args.graphics.add(rangeGraphics);
    }
  }

  protected unloadChildren(olderThan?: BeTimePoint): void {
    const children = this.children;
    if (undefined === children) {
      return;
    }

    if (undefined !== olderThan && (this.isUndisplayableRootTile || this._childrenLastUsed.milliseconds > olderThan.milliseconds)) {
      // this node has been used recently, or should never be unloaded based on expiration time. Keep it, but potentially unload its grandchildren.
      for (const child of children)
        child.unloadChildren(olderThan);
    } else {
      for (const child of children) {
        child.setAbandoned();
        child.dispose();
      }

      this._children = undefined;
      this._childrenLoadStatus = TileTree.LoadStatus.NotLoaded;
    }
  }

  private static _scratchWorldFrustum = new Frustum();
  private static _scratchRootFrustum = new Frustum();
  private static _scratchWorldSphere = new BoundingSphere();
  private static _scratchRootSphere = new BoundingSphere();
  private isCulled(range: ElementAlignedBox3d, args: Tile.DrawArgs, sphere?: BoundingSphere) {
    const box = Frustum.fromRange(range, Tile._scratchRootFrustum);
    const worldBox = box.transformBy(args.location, Tile._scratchWorldFrustum);
    const worldSphere = sphere ? sphere.transformBy(args.location, Tile._scratchWorldSphere) : undefined;

    // Test against frustum.
    if (FrustumPlanes.Containment.Outside === args.frustumPlanes.computeFrustumContainment(worldBox, worldSphere))
      return true;

    // Test against TileTree's own clip volume, if any.
    if (undefined !== args.clip && ClipPlaneContainment.StronglyOutside === args.clip.classifyPointContainment(box.points))
      return true;

    // Test against view clip, if any (will be undefined if TileTree does not want view clip applied to it).
    if (undefined !== args.viewClip && ClipPlaneContainment.StronglyOutside === args.viewClip.classifyPointContainment(worldBox.points))
      return true;

    return false;
  }

  protected loadChildren(): TileTree.LoadStatus {
    if (TileTree.LoadStatus.NotLoaded === this._childrenLoadStatus) {
      this._childrenLoadStatus = TileTree.LoadStatus.Loading;
      this.root.loader.getChildrenProps(this).then((props: TileProps[]) => {
        this._children = [];
        this._childrenLoadStatus = TileTree.LoadStatus.Loaded;
        if (undefined !== props) {
          // If this tile is undisplayable, update its content range based on children's content ranges.
          const parentRange = this.hasContentRange ? undefined : new Range3d();
          for (const prop of props) {
            const child = new Tile(Tile.paramsFromJSON(prop, this.root, this));

            this._children.push(child);
            if (undefined !== parentRange && !child.isEmpty)
              parentRange.extendRange(child.contentRange);
          }

          if (undefined !== parentRange)
            this._contentRange = parentRange;
        }

        if (0 === this._children.length) {
          this._children = undefined;
          this._isLeaf = true;
        } else {
          IModelApp.viewManager.onNewTilesReady();
        }
      }).catch((_err) => {
        this._childrenLoadStatus = TileTree.LoadStatus.NotFound;
        this._children = undefined;
        this._isLeaf = true;
      });
    }

    return this._childrenLoadStatus;
  }

  public debugDump(): string {
    let str = "  ".repeat(this.depth);
    str += this.contentId;
    if (undefined !== this._children) {
      str += " " + this._children.length + "\n";
      for (const child of this._children)
        str += child.debugDump();
    } else {
      str += "\n";
    }

    return str;
  }

  public get request(): TileRequest | undefined { return this._request; }
  public set request(request: TileRequest | undefined) {
    assert(undefined === request || undefined === this.request);
    this._request = request;
  }

  public countDescendants(): number {
    let count = 0;
    if (undefined !== this._children) {
      count = this._children.length;
      for (const child of this._children)
        count += child.countDescendants();
    }

    return count;
  }
}

// tslint:disable:no-const-enum

/** @internal */
export namespace Tile {
  /**
   * Describes the current status of a Tile. Tiles are loaded by making asynchronous requests to the backend.
   * @internal
   */
  export const enum LoadStatus {
    NotLoaded = 0, // No attempt to load the tile has been made, or the tile has since been unloaded. It currently has no graphics.
    Queued = 1, // A request has been made to load the tile from the backend, and a response is pending.
    Loading = 2, // A response has been received and the tile's graphics and other data are being loaded on the frontend.
    Ready = 3, // The tile has been loaded, and if the tile is displayable it has graphics.
    NotFound = 4, // The tile was requested, and the response from the backend indicated the tile could not be found.
    Abandoned = 5, // The tile has been discarded.
  }

  /**
   * Describes the visibility of a tile based on its size and a view frustum.
   * @internal
   */
  export const enum Visibility {
    OutsideFrustum, // this tile is entirely outside of the viewing frustum
    TooCoarse, // this tile is too coarse to be drawn
    Visible, // this tile is of the correct size to be drawn
  }

  /**
   * Returned by Tile.selectTiles() to indicate whether a parent tile should be drawn in place of a child tile.
   * @internal
   */
  export const enum SelectParent {
    No,
    Yes,
  }

  /**
   * Loosely describes the "importance" of a tile. Requests for tiles of more "importance" are prioritized for loading.
   * @note A lower LoadPriority value indicates higher importance.
   * @internal
   */
  export const enum LoadPriority {
    /** Background map tiles. */
    Map = 1,
    /** Typically, tiles generated from the contents of geometric models. */
    Primary = 20,
    /** Terrain -- requires background/map tiles for drape. */
    Terrain = 30,
    /** Typically, context reality models. */
    Context = 40,
    /** Supplementary tiles used to classify the contents of geometric or reality models. */
    Classifier = 50,
  }

  /**
   * Options for displaying tile bounding boxes for debugging purposes.
   *
   * Bounding boxes are color-coded based on refinement strategy:
   *  - Blue: A leaf tile (has no child tiles).
   *  - Green: An ordinary tile (sub-divides into 4 or 8 child tiles).
   *  - Red: A tile which refines to a single higher-resolution child occupying the same volume.
   * @see [[Viewport.debugBoundingBoxes]]
   * @internal
   */
  export const enum DebugBoundingBoxes {
    /** Display no bounding boxes */
    None = 0,
    /** Display boxes representing the tile's full volume. */
    Volume,
    /** Display boxes representing the range of the tile's contents, which may be tighter than (but never larger than) the tile's full volume. */
    Content,
    /** Display both volume and content boxes. */
    Both,
    /** Display boxes for direct children, where blue boxes indicate empty volumes. */
    ChildVolumes,
    /** Display bounding sphere. */
    Sphere,
  }

  /**
   * Arguments used when selecting and drawing tiles
   * @internal
   */
  export class DrawArgs {
    public readonly location: Transform;
    public readonly root: TileTree;
    public clipVolume?: RenderClipVolume;
    public readonly context: SceneContext;
    public viewFrustum?: ViewFrustum;
    public readonly graphics: GraphicBranch = new GraphicBranch();
    public readonly now: BeTimePoint;
    public readonly purgeOlderThan: BeTimePoint;
    private readonly _frustumPlanes?: FrustumPlanes;
    public planarClassifier?: RenderPlanarClassifier;
    public drape?: RenderTextureDrape;
    public readonly viewClip?: ClipVector;
    public parentsAndChildrenExclusive: boolean;

    public getPixelSize(tile: Tile): number {
      const radius = this.getTileRadius(tile); // use a sphere to test pixel size. We don't know the orientation of the image within the bounding box.
      const center = this.getTileCenter(tile);

      const viewPt = this.worldToViewMap.transform0.multiplyPoint3dQuietNormalize(center);
      const viewPt2 = new Point3d(viewPt.x + 1.0, viewPt.y, viewPt.z);
      const pixelSizeAtPt = this.worldToViewMap.transform1.multiplyPoint3dQuietNormalize(viewPt).distance(this.worldToViewMap.transform1.multiplyPoint3dQuietNormalize(viewPt2));
      return 0 !== pixelSizeAtPt ? radius / pixelSizeAtPt : 1.0e-3;
    }

    public get frustumPlanes(): FrustumPlanes {
      return this._frustumPlanes !== undefined ? this._frustumPlanes : this.context.frustumPlanes;
    }
    protected get worldToViewMap(): Map4d {
      return this.viewFrustum ? this.viewFrustum!.worldToViewMap : this.context.viewport.viewFrustum.worldToViewMap;
    }

    public constructor(context: SceneContext, location: Transform, root: TileTree, now: BeTimePoint, purgeOlderThan: BeTimePoint, clip?: RenderClipVolume, parentsAndChildrenExclusive = true) {
      this.location = location;
      this.root = root;
      this.clipVolume = clip;
      this.context = context;
      this.now = now;
      this.purgeOlderThan = purgeOlderThan;
      this.graphics.setViewFlagOverrides(root.viewFlagOverrides);
      this.viewFrustum = context.viewFrustum;
      if (this.viewFrustum !== undefined)
        this._frustumPlanes = new FrustumPlanes(this.viewFrustum.getFrustum());

      this.planarClassifier = context.getPlanarClassifierForModel(root.modelId);
      this.drape = context.getTextureDrapeForModel(root.modelId);

      // NB: Culling is currently feature-gated - ignore view clip if feature not enabled.
      if (context.viewFlags.clipVolume && false !== root.viewFlagOverrides.clipVolumeOverride)
        this.viewClip = context.viewport.view.getViewClip();

      this.graphics.animationId = root.modelId;
      this.parentsAndChildrenExclusive = parentsAndChildrenExclusive;
    }

    /** A multiplier applied to a [[Tile]]'s `maximumSize` property to adjust level of detail.
     * @see [[Viewport.tileSizeModifier]].
     */
    public get tileSizeModifier(): number { return this.context.viewport.tileSizeModifier; }

    public getTileCenter(tile: Tile): Point3d { return this.location.multiplyPoint3d(tile.center); }

    private static _scratchRange = new Range3d();
    public getTileRadius(tile: Tile): number {
      let range: Range3d = tile.range.clone(DrawArgs._scratchRange);
      range = this.location.multiplyRange(range, range);
      return 0.5 * (tile.root.is3d ? range.low.distance(range.high) : range.low.distanceXY(range.high));
    }

    public get clip(): ClipVector | undefined { return undefined !== this.clipVolume ? this.clipVolume.clipVector : undefined; }

    public drawGraphics(): void {
      if (this.graphics.isEmpty)
        return;

      const classifierOrDrape = undefined !== this.planarClassifier ? this.planarClassifier : this.drape;
      const opts = { iModel: this.root.iModel, clipVolume: this.clipVolume, classifierOrDrape };
      const branch = this.context.createGraphicBranch(this.graphics, this.location, opts);

      this.context.outputGraphic(branch);
    }

    public insertMissing(tile: Tile): void {
      this.context.insertMissingTile(tile);
    }

    public markChildrenLoading(): void { this.context.hasMissingTiles = true; }
  }

  /**
   * Parameters used to construct a Tile.
   * @internal
   */
  export interface Params {
    readonly root: TileTree;
    readonly contentId: string;
    readonly range: ElementAlignedBox3d;
    readonly maximumSize: number;
    readonly isLeaf?: boolean;
    readonly parent?: Tile;
    readonly contentRange?: ElementAlignedBox3d;
    readonly transformToRoot?: Transform;
    readonly sizeMultiplier?: number;
  }

  /** @internal */
  export function paramsFromJSON(props: TileProps, root: TileTree, parent?: Tile): Params {
    const contentRange = undefined !== props.contentRange ? Range3d.fromJSON<ElementAlignedBox3d>(props.contentRange) : undefined;
    const transformToRoot = undefined !== props.transformToRoot ? Transform.fromJSON(props.transformToRoot) : undefined;
    return {
      root,
      contentId: props.contentId,
      range: Range3d.fromJSON(props.range),
      maximumSize: props.maximumSize,
      isLeaf: props.isLeaf,
      parent,
      contentRange,
      transformToRoot,
      sizeMultiplier: props.sizeMultiplier,
    };
  }

  /**
   * Describes the contents of a Tile.
   * @internal
   */
  export interface Content {
    /** Graphical representation of the tile's geometry. */
    graphic?: RenderGraphic;
    /** Bounding box tightly enclosing the tile's geometry. */
    contentRange?: ElementAlignedBox3d;
    /** True if this tile requires no subdivision or refinement. */
    isLeaf?: boolean;
    /** If this tile was produced by refinement, the multiplier applied to its screen size. */
    sizeMultiplier?: number;
    /** A bitfield describing empty sub-volumes of this tile's volume. */
    emptySubRangeMask?: number;
  }
}

// Tile.LoadStatus is computed from the combination of Tile._state and, if Tile.request is defined, Tile.request.state.
const enum TileState {
  NotReady = Tile.LoadStatus.NotLoaded, // Tile requires loading, but no request has yet completed.
  Ready = Tile.LoadStatus.Ready, // request completed successfully, or no loading was required.
  NotFound = Tile.LoadStatus.NotFound, // request failed.
  Abandoned = Tile.LoadStatus.Abandoned, // tile was abandoned.
}