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import { SystemNames, System } from ".";
import {
Mass,
BoundingBox,
ComponentNames,
Jump,
Velocity,
Moment,
} 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<number>) =>
entityIds.forEach((id) => {
const entity = game.entities.get(id);
if (!entity.hasComponent(ComponentNames.BoundingBox)) {
return;
}
entitiesToAddToQuadtree.push(entity);
})
);
entitiesToAddToQuadtree.forEach((entity) => {
const boundingBox = entity.getComponent<BoundingBox>(
ComponentNames.BoundingBox
);
this.quadTree.insert(
entity.id,
boundingBox.dimension,
boundingBox.center
);
});
// find colliding entities and perform collisions
const collidingEntities = this.getCollidingEntities(
entitiesToAddToQuadtree,
game.entities
);
collidingEntities.forEach(([entityAId, entityBId]) => {
const [entityA, entityB] = [entityAId, entityBId].map((id) =>
game.entities.get(id)
);
this.performCollision(entityA, entityB);
});
}
private performCollision(entityA: Entity, entityB: Entity) {
const [entityABoundingBox, entityBBoundingBox] = [entityA, entityB].map(
(entity) => entity.getComponent<BoundingBox>(ComponentNames.BoundingBox)
);
let velocity: Velocity;
if (entityA.hasComponent(ComponentNames.Velocity)) {
velocity = entityA.getComponent<Velocity>(ComponentNames.Velocity);
}
if (
entityA.hasComponent(ComponentNames.Collide) &&
entityB.hasComponent(ComponentNames.TopCollidable) &&
entityABoundingBox.center.y <= entityBBoundingBox.center.y &&
velocity &&
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
velocity.dCartesian.dy = 0;
// apply normal force
if (entityA.hasComponent(ComponentNames.Gravity)) {
const mass = entityA.getComponent<Mass>(ComponentNames.Mass).mass;
const F_n = -mass * PhysicsConstants.GRAVITY;
entityA.getComponent<Forces>(ComponentNames.Forces).forces.push({
fCartesian: { fy: F_n },
});
}
// reset the entities' jump
if (entityA.hasComponent(ComponentNames.Jump)) {
entityA.getComponent<Jump>(ComponentNames.Jump).canJump = true;
}
entityABoundingBox.center.y =
entityBBoundingBox.center.y -
entityBBoundingBox.dimension.height / 2 -
this.getDyToPushOutOfFloor(entityABoundingBox, entityBBoundingBox);
}
}
private getCollidingEntities(
collidableEntities: Entity[],
entityMap: Map<number, Entity>
): [number, number][] {
const collidingEntityIds: [number, number] = [];
for (const entity of collidableEntities) {
const boundingBox = entity.getComponent<BoundingBox>(
ComponentNames.BoundingBox
);
this.quadTree
.getNeighborIds({
id: entity.id,
dimension: boundingBox.dimension,
center: boundingBox.center,
})
.filter((neighborId) => neighborId != entity.id)
.forEach((neighborId) => {
const neighborBoundingBox = entityMap
.get(neighborId)
.getComponent<BoundingBox>(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 {
rotation,
center: { x, y },
dimension: { width, height },
} = entityBoundingBox;
let rads = rotation * (Math.PI / 180);
if (rads >= Math.PI) {
rads -= Math.PI; // we have symmetry so we can skip two cases
}
let boundedCollisionX = 0; // bounded x on the surface from width
let clippedX = 0; // x coordinate of the vertex below the surface
let outScribedRectangleHeight, dy, dx;
if (rads <= Math.PI / 2) {
dx = (width * Math.cos(rads) - height * Math.sin(rads)) / 2;
outScribedRectangleHeight =
width * Math.sin(rads) + height * Math.cos(rads);
} else if (rads <= Math.PI) {
rads -= Math.PI / 2;
dx = (height * Math.cos(rads) - width * Math.sin(rads)) / 2;
outScribedRectangleHeight =
width * Math.cos(rads) + height * Math.sin(rads);
}
if (x >= floorBoundingBox.center.x) {
clippedX = x + dx;
boundedCollisionX = Math.min(
floorBoundingBox.center.x + floorBoundingBox.dimension.width / 2,
clippedX
);
return (
outScribedRectangleHeight / 2 -
Math.max((clippedX - boundedCollisionX) * Math.tan(rads), 0)
);
}
clippedX = x - dx;
boundedCollisionX = Math.max(
floorBoundingBox.center.x - floorBoundingBox.dimension.width / 2,
clippedX
);
return (
outScribedRectangleHeight / 2 -
Math.max((boundedCollisionX - clippedX) * Math.tan(rads), 0)
);
}
}
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