feat(geom): add splitArclength()

Author: postspectacular

packages/geom/package.json

@@ -334,6 +334,9 @@
 		"./sphere": {
 			"default": "./sphere.js"
 		},
+		"./split-arclength": {
+			"default": "./split-arclength.js"
+		},
 		"./split-at": {
 			"default": "./split-at.js"
 		},

packages/geom/src/index.ts

@@ -71,6 +71,7 @@ export * from "./rotate.js";
 export * from "./scale.js";
 export * from "./scatter.js";
 export * from "./simplify.js";
+export * from "./split-arclength.js";
 export * from "./split-at.js";
 export * from "./split-near.js";
 export * from "./subdiv-curve.js";

packages/geom/src/split-arclength.ts

@@ -0,0 +1,68 @@
+import type { MultiFn2 } from "@thi.ng/defmulti";
+import { DEFAULT, defmulti } from "@thi.ng/defmulti/defmulti";
+import type { IHiccupShape, IShape } from "@thi.ng/geom-api";
+import { Sampler } from "@thi.ng/geom-resample/sampler";
+import { mapcat } from "@thi.ng/transducers/mapcat";
+import type { Vec } from "@thi.ng/vectors";
+import { Group } from "./api/group.js";
+import { Polyline } from "./api/polyline.js";
+import { asPolyline } from "./as-polyline.js";
+import { __copyAttribs } from "./internal/copy.js";
+import { __dispatch } from "./internal/dispatch.js";
+import { __pointArraysAsShapes } from "./internal/points-as-shape.js";
+
+/**
+ * Splits given shape into {@link Polyline} segments of given (max) arc length.
+ * Returns array of new shapes/polylines.
+ *
+ * @remarks
+ * Currently only implemented for:
+ *
+ * - {@link Group}
+ * - {@link Polyline}
+ *
+ * Other shape types will be attempted to be auto-converted via
+ * {@link asPolyline} first.
+ *
+ * @param shape
+ * @param dist
+ */
+export const splitArclength: MultiFn2<IShape, number, IShape[]> = defmulti<
+	any,
+	number,
+	IShape[]
+>(
+	__dispatch,
+	{},
+	{
+		[DEFAULT]: ($: IShape, d: number) => splitArclength(asPolyline($), d),
+
+		group: ($, d) => [
+			new Group(__copyAttribs($.attribs), [
+				...mapcat(
+					(c: IShape) => <IHiccupShape[]>splitArclength(c, d),
+					$.children
+				),
+			]),
+		],
+
+		polyline: ($: Polyline, d) => {
+			const chunks: Vec[][] = [];
+			let pts = $.points;
+			while (true) {
+				const sampler = new Sampler(pts);
+				const total = sampler.totalLength();
+				if (total > d) {
+					const parts = sampler.splitAt(d / total);
+					if (!parts) break;
+					chunks.push(parts[0]);
+					pts = parts[1];
+				} else {
+					chunks.push(pts);
+					break;
+				}
+			}
+			return __pointArraysAsShapes(Polyline, chunks, $.attribs)!;
+		},
+	}
+);