add Circle

src/2d.js

@@ -2,12 +2,50 @@ function sqr(x) {
 	return x * x;
 }
 
+export class Circle {
+	constructor(o, r) {
+		this.o = o;
+		this.r = r;
+	}
+
+	clone() {
+		return new Circle(this.o.clone(), this.r);
+	}
+
+	equal(c) {
+		return this.o.equal(c.o) && this.r == c.r;
+	}
+
+	static intersect(a, b) {
+		return a.o.sub(b.o).norm() <= sqr(a.r + b.r);
+	}
+
+	static collisionElimation(a, b) {
+		if (!Circle.intersect(a, b)) { return false; }
+		const d = a.o.distanceTo(b.o);
+		const ad = (sqr(a.r) - sqr(b.r) + sqr(d)) / (2 * d);
+		const bd = d - ad;
+		const v = b.o.sub(a.o);
+		a.o.subTo(v.adjust(a.r - ad));
+		b.o.addTo(v.adjust(b.r - bd));
+		return true;
+	}
+}
+
 export class Vec2 {
 	constructor(x, y) {
 		this.x = x || 0;
 		this.y = y || 0;
 	}
 
+	adjust(len) {
+		return this.mul(len / this.abs());
+	}
+
+	distanceTo(b) {
+		return this.sub(b).abs();
+	}
+
 	add(y) {
 		return new Vec2(this.x + y.x, this.y + y.y);
 	}

tests/2d.test.js

@@ -1,5 +1,5 @@
 import assert from 'node:assert';
-import { Vec2 } from '../src/2d.js';
+import { Vec2, Circle } from '../src/2d.js';
 
 describe('Vec2', function () {
 	it('construct', function() {
@@ -49,4 +49,20 @@ describe('Vec2', function () {
 		assert.equal(p.dot(q), 10);
 		assert.equal(p.cross(q), -10);
 	});
+
+	it('circle intersect', function() {
+		let c1 = new Circle(new Vec2(0, 0), 1);
+		let c2 = new Circle(new Vec2(0, 1.5), 1);
+		let c3 = new Circle(new Vec2(2, 2), 1);
+		assert.ok(Circle.intersect(c1, c2));
+		assert.ok(!Circle.intersect(c1, c3));
+	});
+
+	it('circle collision elimation', function() {
+		let c1 = new Circle(new Vec2(0, 0), 1);
+		let c2 = new Circle(new Vec2(0, 1.5), 1);
+		assert.ok(Circle.collisionElimation(c1, c2));
+		assert.ok(c1.equal(new Circle(new Vec2(0, -.25), 1)));
+		assert.ok(c2.equal(new Circle(new Vec2(0, 1.75), 1)));
+	});
 });