From 884a5b700c6c924a0d85e656e83994069ee3f716 Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Sun, 4 Nov 2018 20:05:12 +0100
Subject: Add simple math library for line segments

---
 src/math/line.ts | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100644 src/math/line.ts

diff --git a/src/math/line.ts b/src/math/line.ts
new file mode 100644
index 0000000..98e126b
--- /dev/null
+++ b/src/math/line.ts
@@ -0,0 +1,98 @@
+import { mat2, vec2 } from 'gl-matrix';
+
+const rot90 = mat2.fromRotation(mat2.create(), Math.PI / 2);
+
+export function normal(out: vec2, a: vec2): vec2 {
+	return vec2.transformMat2(out, a, rot90);
+}
+
+export function crossz(a: vec2, b: vec2): number {
+	return a[0] * b[1] - a[1] * b[0];
+}
+
+export class Line {
+	constructor(
+		public readonly p: vec2,
+		public readonly v: vec2,
+	) {}
+
+	public projectPointDistance(p2: vec2): number {
+		const v2 = vec2.sub(vec2.create(), p2, this.p);
+		return vec2.dot(this.v, v2);
+	}
+
+	public projectPoint(out: vec2, p2: vec2): vec2 {
+		const d = this.projectPointDistance(p2);
+		return vec2.scaleAndAdd(out, this.p, this.v, d);
+	}
+
+	public distancePoint(p2: vec2): number {
+		const v2 = vec2.sub(vec2.create(), p2, this.p);
+		return crossz(this.v, v2);
+	}
+
+	public intersectLine(out: vec2, l2: Line): vec2 {
+		const vp = vec2.sub(vec2.create(), l2.p, this.p);
+		const d = crossz(vp, this.v);
+		const d2 = d / crossz(this.v, l2.v);
+		return vec2.scaleAndAdd(out, l2.p, l2.v, d2);
+	}
+
+	public equals(l2: Line): boolean {
+		return vec2.equals(this.p, l2.p) && vec2.equals(this.v, l2.v);
+	}
+}
+
+export class LineSegment extends Line {
+	public static fromPoints(p1: vec2, p2: vec2): LineSegment {
+		const d = vec2.dist(p1, p2);
+		const v = vec2.sub(vec2.create(), p2, p1);
+		vec2.scale(v, v, 1 / d);
+
+		return new LineSegment(p1, v, d);
+	}
+
+	constructor(
+		p: vec2,
+		v: vec2,
+		public readonly l: number,
+	) {
+		super(p, v);
+	}
+
+	public getP2(out: vec2): vec2 {
+		return vec2.scaleAndAdd(out, this.p, this.v, this.l);
+	}
+
+	public collidesPoint(p2: vec2): boolean {
+		const d = this.projectPointDistance(p2);
+		return (d >= 0 && d <= this.l);
+	}
+
+	public collidesLine(l2: Line): boolean {
+		const x = this.intersectLine(vec2.create(), l2);
+		return this.collidesPoint(x);
+	}
+
+	public collidesLineSegment(l2: LineSegment): boolean {
+		const x = this.intersectLine(vec2.create(), l2);
+		if (!this.collidesPoint(x))
+			return false;
+		if (!l2.collidesPoint(x))
+			return false;
+
+		return true;
+	}
+
+	public collidesMove(move: LineSegment): boolean {
+		if (!this.collidesLineSegment(move))
+			return false;
+
+		const p2 = move.getP2(vec2.create());
+		return this.distancePoint(p2) < 0;
+	}
+
+	public equals(l2: LineSegment): boolean {
+		return super.equals(l2) && this.l === l2.l;
+	}
+}
-- 
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