jumpstorm/engine/structures/QuadTree.ts

import type { Coord2D, Dimension2D } from '../interfaces';
import type { BoxedEntry, RefreshingCollisionFinderBehavior } from '.';

enum Quadrant {
  I,
  II,
  III,
  IV
}

/*
  unused due to performance problems. here anyways, in case it _really_ is necessary at some point
  (and to justify the amount of time i spent here).
*/
export class QuadTree implements RefreshingCollisionFinderBehavior {
  private static readonly QUADTREE_MAX_LEVELS = 3;
  private static readonly QUADTREE_SPLIT_THRESHOLD = 2000;

  private maxLevels: number;
  private splitThreshold: number;
  private level: number;
  private topLeft: Coord2D;
  private dimension: Dimension2D;

  private children: Map<Quadrant, QuadTree>;
  private objects: BoxedEntry[];

  constructor(
    topLeft: Coord2D = { x: 0, y: 0 },
    dimension: Dimension2D,
    maxLevels: number = QuadTree.QUADTREE_MAX_LEVELS,
    splitThreshold: number = QuadTree.QUADTREE_SPLIT_THRESHOLD,
    level: number = 0
  ) {
    this.children = new Map<Quadrant, QuadTree>();
    this.objects = [];

    this.maxLevels = maxLevels;
    this.splitThreshold = splitThreshold;
    this.level = level;

    this.topLeft = topLeft;
    this.dimension = dimension;
  }

  public insert(boxedEntry: BoxedEntry): void {
    if (this.hasChildren()) {
      this.getQuadrants(boxedEntry).forEach((quadrant) => {
        const quadrantBox = this.children.get(quadrant);
        quadrantBox!.insert(boxedEntry);
      });
      return;
    }

    this.objects.push(boxedEntry);

    if (
      this.objects.length > this.splitThreshold &&
      this.level < this.maxLevels
    ) {
      if (!this.hasChildren()) {
        this.performSplit();
      }
      this.realignObjects();
    }
  }

  public clear(): void {
    this.objects = [];

    if (this.hasChildren()) {
      this.children.forEach((child) => child.clear());
      this.children.clear();
    }
  }

  public getNeighborIds(boxedEntry: BoxedEntry): Set<string> {
    const neighbors = new Set<string>(
      this.objects.map(({ id }) => id).filter((id) => id != boxedEntry.id)
    );

    if (this.hasChildren()) {
      this.getQuadrants(boxedEntry).forEach((quadrant) => {
        const quadrantBox = this.children.get(quadrant);
        quadrantBox
          ?.getNeighborIds(boxedEntry)
          .forEach((id) => neighbors.add(id));
      });
    }

    return neighbors;
  }

  private performSplit(): void {
    const halfWidth = this.dimension.width / 2;
    const halfHeight = this.dimension.height / 2;

    (
      [
        [Quadrant.I, { x: this.topLeft.x + halfWidth, y: this.topLeft.y }],
        [Quadrant.II, { ...this.topLeft }],
        [Quadrant.III, { x: this.topLeft.x, y: this.topLeft.y + halfHeight }],
        [
          Quadrant.IV,
          { x: this.topLeft.x + halfWidth, y: this.topLeft.y + halfHeight }
        ]
      ] as [Quadrant, Coord2D][]
    ).forEach(([quadrant, pos]) => {
      this.children.set(
        quadrant,
        new QuadTree(
          pos,
          { width: halfWidth, height: halfHeight },
          this.maxLevels,
          this.splitThreshold,
          this.level + 1
        )
      );
    });
  }

  private getQuadrants(boxedEntry: BoxedEntry): Quadrant[] {
    const treeCenter: Coord2D = {
      x: this.topLeft.x + this.dimension.width / 2,
      y: this.topLeft.y + this.dimension.height / 2
    };

    return (
      [
        [
          Quadrant.I,
          (x: number, y: number) => x >= treeCenter.x && y < treeCenter.y
        ],
        [
          Quadrant.II,
          (x: number, y: number) => x < treeCenter.x && y < treeCenter.y
        ],
        [
          Quadrant.III,
          (x: number, y: number) => x < treeCenter.x && y >= treeCenter.y
        ],
        [
          Quadrant.IV,
          (x: number, y: number) => x >= treeCenter.x && y >= treeCenter.y
        ]
      ] as [Quadrant, (x: number, y: number) => boolean][]
    )
      .filter(
        ([_quadrant, condition]) =>
          condition(
            boxedEntry.center.x + boxedEntry.dimension.width / 2,
            boxedEntry.center.y + boxedEntry.dimension.height / 2
          ) ||
          condition(
            boxedEntry.center.x - boxedEntry.dimension.width / 2,
            boxedEntry.center.y - boxedEntry.dimension.height / 2
          )
      )
      .map(([quadrant]) => quadrant);
  }

  private realignObjects(): void {
    this.objects.forEach((boxedEntry) => {
      this.getQuadrants(boxedEntry).forEach((quadrant) => {
        const quadrantBox = this.children.get(quadrant);
        quadrantBox!.insert(boxedEntry);
      });
    });

    this.objects = [];
  }

  private hasChildren() {
    return this.children && this.children.size > 0;
  }

  public setTopLeft(topLeft: Coord2D) {
    this.topLeft = topLeft;
  }

  public setDimension(dimension: Dimension2D) {
    this.dimension = dimension;
  }
}