feat(geom): add scaleWithCenter()

Author: postspectacular

packages/geom/src/index.ts

@@ -73,6 +73,7 @@ export * from "./point-inside.js";
 export * from "./resample.js";
 export * from "./rotate.js";
 export * from "./scale.js";
+export * from "./scale-with-center.js";
 export * from "./scatter.js";
 export * from "./simplify.js";
 export * from "./split-arclength.js";

packages/geom/src/scale-with-center.ts

@@ -0,0 +1,27 @@
+import type { IShape } from "@thi.ng/geom-api";
+import type { ReadonlyVec } from "@thi.ng/vectors";
+import { mulN } from "@thi.ng/vectors/muln";
+import { scale } from "./scale.js";
+import { translate } from "./translate.js";
+
+/**
+ * Applies a sequence of translate and scale operations to return an uniformly
+ * scaled version of the given shape using `center` as the point of reference.
+ *
+ * @remarks
+ * This op is likely slower than using {@link transform} with a equivalent
+ * transformation matrix (e.g. using [`scaleWithCenter()` from
+ * thi.ng/matrices](https://docs.thi.ng/umbrella/matrices/functions/scaleWithCenter23.html)),
+ * but will not change the shape type (as might be the case with `transform()`).
+ *
+ * Also see: {@link scale}, {@link translate}, {@link applyTransforms}.
+ *
+ * @param shape
+ * @param center
+ * @param factor
+ */
+export const scaleWithCenter = (
+	shape: IShape,
+	center: ReadonlyVec,
+	factor: number
+) => translate(scale(translate(shape, mulN([], center, -1)), factor), center);