123 lines
3.6 KiB
TypeScript
123 lines
3.6 KiB
TypeScript
import { Component, ComponentNames } from '.';
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import type { Coord2D, Dimension2D } from '../interfaces';
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import { dotProduct, rotateVector } from '../utils';
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export class BoundingBox extends Component {
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public center: Coord2D;
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public dimension: Dimension2D;
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public rotation: number;
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constructor(center: Coord2D, dimension: Dimension2D, rotation?: number) {
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super(ComponentNames.BoundingBox);
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this.center = center;
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this.dimension = dimension;
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this.rotation = rotation ?? 0;
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}
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public isCollidingWith(box: BoundingBox): boolean {
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// optimization; when neither rotates just check if they overlap
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if (this.rotation == 0 && box.rotation == 0) {
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const thisTopLeft = this.getTopLeft();
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const thisBottomRight = this.getBottomRight();
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const thatTopLeft = box.getTopLeft();
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const thatBottomRight = box.getBottomRight();
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if (
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thisBottomRight.x <= thatTopLeft.x ||
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thisTopLeft.x >= thatBottomRight.x ||
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thisBottomRight.y <= thatTopLeft.y ||
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thisTopLeft.y >= thatBottomRight.y
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) {
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return false;
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}
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return true;
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}
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// https://en.wikipedia.org/wiki/Hyperplane_separation_theorem
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const boxes = [this.getVertices(), box.getVertices()];
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for (const poly of boxes) {
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for (let i = 0; i < poly.length; i++) {
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const [A, B] = [poly[i], poly[(i + 1) % poly.length]];
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const normal: Coord2D = { x: B.y - A.y, y: A.x - B.x };
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const [[minThis, maxThis], [minBox, maxBox]] = boxes.map((box) =>
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box.reduce(
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([min, max], vertex) => {
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const projection = dotProduct(normal, vertex);
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return [Math.min(min, projection), Math.max(max, projection)];
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},
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[Infinity, -Infinity]
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)
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);
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if (maxThis < minBox || maxBox < minThis) return false;
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}
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}
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return true;
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}
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public getVertices(): Coord2D[] {
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return [
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{ x: -this.dimension.width / 2, y: -this.dimension.height / 2 },
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{ x: -this.dimension.width / 2, y: this.dimension.height / 2 },
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{ x: this.dimension.width / 2, y: this.dimension.height / 2 },
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{ x: this.dimension.width / 2, y: -this.dimension.height / 2 }
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]
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.map((vertex) => rotateVector(vertex, this.rotation)) // rotate
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.map((vertex) => {
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// translate
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return {
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x: vertex.x + this.center.x,
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y: vertex.y + this.center.y
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};
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});
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}
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public getRotationInPiOfUnitCircle(): number {
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let rads = this.rotation * (Math.PI / 180);
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if (rads >= Math.PI) {
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// Physics system guarantees rotation \in [0, 360)
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rads -= Math.PI;
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}
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return rads;
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}
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public getOutscribedBoxDims(): Dimension2D {
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let rads = this.getRotationInPiOfUnitCircle();
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const { width, height } = this.dimension;
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if (rads == 0) return this.dimension;
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if (rads <= Math.PI / 2) {
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return {
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width: Math.abs(height * Math.sin(rads) + width * Math.cos(rads)),
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height: Math.abs(width * Math.sin(rads) + height * Math.cos(rads))
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};
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}
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rads -= Math.PI / 2;
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return {
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width: Math.abs(height * Math.cos(rads) + width * Math.sin(rads)),
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height: Math.abs(width * Math.cos(rads) + height * Math.sin(rads))
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};
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}
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public getTopLeft(): Coord2D {
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return {
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x: this.center.x - this.dimension.width / 2,
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y: this.center.y - this.dimension.height / 2
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};
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}
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public getBottomRight(): Coord2D {
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return {
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x: this.center.x + this.dimension.width / 2,
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y: this.center.y + this.dimension.height / 2
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};
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}
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}
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