init

lib/Segment.ts

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+import { lerp } from "./lerp.ts";
+import type { Vector } from "./Vector.ts";
+
+export type Segment = [Vector, Vector];
+
+export type SegmentIntersection = {
+	position: Vector;
+	offset: number;
+};
+
+export function createSegmentIntersection(): SegmentIntersection {
+	return {
+		position: {
+			x: Number.NaN,
+			y: Number.NaN,
+		},
+		offset: Number.NaN,
+	};
+}
+
+export function setSegmentIntersection(
+	segmentIntersection: SegmentIntersection,
+	a: Segment,
+	b: Segment,
+): void {
+	const bottom =
+		(b[1].y - b[0].y) * (a[1].x - a[0].x) -
+		(b[1].x - b[0].x) * (a[1].y - a[0].y);
+
+	if (bottom === 0) {
+		segmentIntersection.position.x = Number.NaN;
+		segmentIntersection.position.y = Number.NaN;
+		segmentIntersection.offset = Number.NaN;
+
+		return;
+	}
+
+	const tTop =
+		(b[1].x - b[0].x) * (a[0].y - b[0].y) -
+		(b[1].y - b[0].y) * (a[0].x - b[0].x);
+	const uTop =
+		(b[0].y - a[0].y) * (a[0].x - a[1].x) -
+		(b[0].x - a[0].x) * (a[0].y - a[1].y);
+
+	const t = tTop / bottom;
+	const u = uTop / bottom;
+
+	if (t < 0 || t > 1 || u < 0 || u > 1) {
+		segmentIntersection.position.x = Number.NaN;
+		segmentIntersection.position.y = Number.NaN;
+		segmentIntersection.offset = Number.NaN;
+
+		return;
+	}
+
+	segmentIntersection.position.x = lerp(a[0].x, a[1].x, t);
+	segmentIntersection.position.y = lerp(a[0].y, a[1].y, t);
+	segmentIntersection.offset = t;
+}
+
+export function drawSegment(
+	segment: Segment,
+	ctx: CanvasRenderingContext2D,
+	color: string,
+): void {
+	ctx.lineWidth = 2;
+	ctx.strokeStyle = color;
+	ctx.beginPath();
+	ctx.moveTo(segment[0].x, segment[0].y);
+	ctx.lineTo(segment[1].x, segment[1].y);
+	ctx.stroke();
+}