import { SystemNames, System } from "."; import { Mass, BoundingBox, ComponentNames, Jump, Velocity, Forces, } from "../components"; import { Game } from "../Game"; import { PhysicsConstants } from "../config"; import { Entity } from "../entities"; import type { Dimension2D } from "../interfaces"; import { QuadTree } from "../structures"; export class Collision extends System { private static readonly COLLIDABLE_COMPONENT_NAMES = [ ComponentNames.Collide, ComponentNames.TopCollidable, ]; private static readonly QUADTREE_MAX_LEVELS = 10; private static readonly QUADTREE_SPLIT_THRESHOLD = 10; private quadTree: QuadTree; constructor(screenDimensions: Dimension2D) { super(SystemNames.Collision); this.quadTree = new QuadTree( { x: 0, y: 0 }, screenDimensions, Collision.QUADTREE_MAX_LEVELS, Collision.QUADTREE_SPLIT_THRESHOLD, ); } public update(_dt: number, game: Game) { // rebuild the quadtree this.quadTree.clear(); const entitiesToAddToQuadtree: Entity[] = []; Collision.COLLIDABLE_COMPONENT_NAMES.map((componentName) => game.componentEntities.get(componentName), ).forEach( (entityIds?: Set) => entityIds?.forEach((id) => { const entity = game.entities.get(id); if (!entity || !entity.hasComponent(ComponentNames.BoundingBox)) { return; } entitiesToAddToQuadtree.push(entity); }), ); entitiesToAddToQuadtree.forEach((entity) => { const boundingBox = entity.getComponent( ComponentNames.BoundingBox, ); let dimension = { ...boundingBox.dimension }; if (boundingBox.rotation != 0) { dimension = boundingBox.getOutscribedBoxDims(); } this.quadTree.insert(entity.id, dimension, boundingBox.center); }); // find colliding entities and perform collisions const collidingEntities = this.getCollidingEntities( entitiesToAddToQuadtree, game, ); collidingEntities.forEach(([entityAId, entityBId]) => { const [entityA, entityB] = [entityAId, entityBId].map((id) => game.entities.get(id), ); if (entityA && entityB) { this.performCollision(entityA, entityB); } }); } private performCollision(entityA: Entity, entityB: Entity) { const [entityABoundingBox, entityBBoundingBox] = [entityA, entityB].map( (entity) => entity.getComponent(ComponentNames.BoundingBox), ); let velocity = new Velocity(); if (entityA.hasComponent(ComponentNames.Velocity)) { velocity = entityA.getComponent(ComponentNames.Velocity); } if ( entityA.hasComponent(ComponentNames.Collide) && entityB.hasComponent(ComponentNames.TopCollidable) && entityABoundingBox.center.y <= entityBBoundingBox.center.y && velocity.dCartesian.dy >= 0 // don't apply "floor" logic when coming through the bottom ) { if (entityBBoundingBox.rotation != 0) { throw new Error( `entity with id ${entityB.id} has TopCollidable component and a non-zero rotation. that is not (yet) supported.`, ); } // remove previous velocity in the y axis if (velocity) velocity.dCartesian.dy = 0; // apply normal force if (entityA.hasComponent(ComponentNames.Gravity)) { const mass = entityA.getComponent(ComponentNames.Mass).mass; const F_n = -mass * PhysicsConstants.GRAVITY; entityA.getComponent(ComponentNames.Forces).forces.push({ fCartesian: { fy: F_n, fx: 0 }, torque: 0, }); } // reset the entities' jump if (entityA.hasComponent(ComponentNames.Jump)) { entityA.getComponent(ComponentNames.Jump).canJump = true; } entityABoundingBox.center.y = entityBBoundingBox.center.y - entityBBoundingBox.dimension.height / 2 - this.getDyToPushOutOfFloor(entityABoundingBox, entityBBoundingBox); } } private getCollidingEntities( collidableEntities: Entity[], game: Game, ): [number, number][] { const collidingEntityIds: [number, number][] = []; for (const entity of collidableEntities) { const boundingBox = entity.getComponent( ComponentNames.BoundingBox, ); const neighborIds = this.quadTree .getNeighborIds({ id: entity.id, dimension: boundingBox.dimension, center: boundingBox.center, }) .filter((neighborId) => neighborId != entity.id); neighborIds.forEach((neighborId) => { const neighbor = game.getEntity(neighborId); if (!neighbor) return; const neighborBoundingBox = neighbor.getComponent( ComponentNames.BoundingBox, ); if (boundingBox.isCollidingWith(neighborBoundingBox)) { collidingEntityIds.push([entity.id, neighborId]); } }); } return collidingEntityIds; } // ramblings: https://excalidraw.com/#json=z-xD86Za4a3duZuV2Oky0,KaGe-5iHJu1Si8inEo4GLQ private getDyToPushOutOfFloor( entityBoundingBox: BoundingBox, floorBoundingBox: BoundingBox, ): number { const { dimension: { width, height }, center: { x }, } = entityBoundingBox; const outScribedRectangle = entityBoundingBox.getOutscribedBoxDims(); let rads = entityBoundingBox.getRotationInPiOfUnitCircle(); let dx = (width * Math.cos(rads) - height * Math.sin(rads)) / 2; if (rads >= Math.PI / 2) { rads -= Math.PI / 2; dx = (height * Math.cos(rads) - width * Math.sin(rads)) / 2; } const clippedX = x + dx; // x coordinate of the vertex below the surface (if existant) let boundedCollisionX = 0; // bounded x on the surface from width if (x >= floorBoundingBox.center.x) { boundedCollisionX = Math.min( floorBoundingBox.center.x + floorBoundingBox.dimension.width / 2, clippedX, ); return ( outScribedRectangle.height / 2 - Math.max((clippedX - boundedCollisionX) * Math.tan(rads), 0) ); } boundedCollisionX = Math.max( floorBoundingBox.center.x - floorBoundingBox.dimension.width / 2, clippedX, ); return ( outScribedRectangle.height / 2 - Math.max((boundedCollisionX - clippedX) * Math.tan(Math.PI / 2 - rads), 0) ); } }