vertecs/src/physics/broadphase/sap/SweepAndPruneBroadphase.ts

A typescript entity-component-system framework

import Broadphase from "../Broadphase";
import { Entity } from "../../../core";
import Body from "../../bodies/Body";
import Endpoint from "./Endpoint";

export default class SweepAndPruneBroadphase extends Broadphase {
    readonly #potentialCollisionPairs: [Entity, Entity][];

    readonly #endpoints: Endpoint[][];

    public constructor() {
        super();
        // X, Y, Z axes
        this.#endpoints = [[], [], []];
        this.#potentialCollisionPairs = [];
    }

    public onEntityAdded(entity: Entity): void {
        const body = entity.getComponent(Body);

        if (!body) {
            throw new Error("Entity must have a Body component");
        }

        for (let i = 0; i < this.#endpoints.length; i++) {
            this.#endpoints[i].push(
                new Endpoint(body.getBoundingBox().minimum[i], true, entity),
                new Endpoint(body.getBoundingBox().maximum[i], false, entity)
            );
        }
    }

    public onEntityRemoved(entity: Entity): void {
        this.#endpoints.forEach((axis) => {
            // Find the indices of the entity's endpoints
            const minIndex = axis.findIndex(
                (endpoint) => endpoint.entity === entity && endpoint.isMinimum
            );
            const maxIndex = axis.findIndex(
                (endpoint) => endpoint.entity === entity && !endpoint.isMinimum
            );

            // Remove the endpoints by splicing them out of the array
            if (minIndex !== -1) axis.splice(minIndex, 1);
            if (maxIndex !== -1) axis.splice(maxIndex, 1);
        });

        this.updateCollisionPairs();
    }

    public onEntityMoved(entity: Entity): void {
        const body = entity.getComponent(Body);

        if (!body) {
            throw new Error("Entity must have a Body component");
        }

        this.#endpoints.forEach((axis, index) => {
            const minEndpoint = axis.find(
                (endpoint) => endpoint.entity === entity && endpoint.isMinimum
            );
            const maxEndpoint = axis.find(
                (endpoint) => endpoint.entity === entity && !endpoint.isMinimum
            );

            if (minEndpoint)
                minEndpoint.value = body.getBoundingBox().minimum[index];
            if (maxEndpoint)
                maxEndpoint.value = body.getBoundingBox().maximum[index];
        });

        this.updateCollisionPairs();
    }

    public getCollisionPairs(entities: Entity[]): [Entity, Entity][] {
        return this.#potentialCollisionPairs;
    }

    private updateCollisionPairs(): void {
        this.sortEndpoints();
        this.#potentialCollisionPairs.length = 0;

        this.#endpoints.forEach((axis) => {
            const activeList: Entity[] = [];

            axis.forEach((endpoint) => {
                if (endpoint.isMinimum) {
                    for (let i = 0; i < activeList.length; i++) {
                        const active = activeList[i];
                        const pair: [Entity, Entity] = [
                            active,
                            endpoint.entity,
                        ].sort() as [Entity, Entity];

                        // Check if the pair already exists in the potential collisions
                        if (
                            !this.#potentialCollisionPairs.some(
                                (collision) =>
                                    collision[0] === pair[0] &&
                                    collision[1] === pair[1]
                            )
                        ) {
                            this.#potentialCollisionPairs.push(pair);
                        }
                    }
                    activeList.push(endpoint.entity);
                } else {
                    const index = activeList.indexOf(endpoint.entity);
                    if (index !== -1) {
                        activeList.splice(index, 1);
                    }
                }
            });
        });
    }

    private sortEndpoints(): void {
        this.#endpoints.forEach((axis) => {
            axis.sort(
                (a, b) =>
                    a.value - b.value ||
                    Number(b.isMinimum) - Number(a.isMinimum)
            );
        });
    }
}