feat(geom): update pathFromCubics() to auto-create sub-paths if needed

packages/geom/src/path.ts

@@ -1,8 +1,10 @@
+import type { Maybe } from "@thi.ng/api";
 import { isNumber } from "@thi.ng/checks/is-number";
 import type { Attribs, PathSegment } from "@thi.ng/geom-api";
 import { map } from "@thi.ng/transducers/map";
 import { mapcat } from "@thi.ng/transducers/mapcat";
-import type { Vec } from "@thi.ng/vectors";
+import type { ReadonlyVec, Vec } from "@thi.ng/vectors";
+import { equals2 } from "@thi.ng/vectors/equals";
 import { maddN2 } from "@thi.ng/vectors/maddn";
 import type { Cubic } from "./api/cubic.js";
 import { Path } from "./api/path.js";
@@ -15,12 +17,38 @@ export const path = (
 	attribs?: Attribs
 ) => new Path(segments, subPaths, attribs);
 
+/**
+ * Constructs a {@link Path} from given sequence of cubic curves, with optional
+ * `attribs`.
+ *
+ * @remarks
+ * If no `attribs` are given, those from the first curve will be used.
+ *
+ * For each successive curve segment, if the start point of the current curve is
+ * not the same as the last point of the previous curve, a new sub path will be
+ * started.
+ *
+ * @param cubics
+ * @param attribs
+ */
 export const pathFromCubics = (cubics: Cubic[], attribs?: Attribs) => {
-	const path = new Path([], [], attribs || cubics[0].attribs);
-	path.segments.push({ type: "m", point: cubics[0].points[0] });
+	let subPaths: PathSegment[][] = [];
+	let curr: PathSegment[];
+	let lastP: Maybe<ReadonlyVec>;
+	const $beginPath = (c: Cubic) => {
+		curr = [{ type: "m", point: c.points[0] }];
+		subPaths.push(curr);
+	};
 	for (let c of cubics) {
-		path.segments.push({ type: "c", geo: c });
+		if (!(lastP && equals2(lastP, c.points[0]))) $beginPath(c);
+		curr!.push({ type: "c", geo: c });
+		lastP = c.points[3];
 	}
+	const path = new Path(
+		subPaths[0],
+		subPaths.slice(1),
+		attribs || cubics[0].attribs
+	);
 	return path;
 };