time for a snapshot

workshop/steps/09-slide/slide.ts

@@ -0,0 +1,11 @@
+import { dot, scale, sub, type Vec } from "./given.ts";
+
+/**
+ * Remove the component of `v` that points into a wall with the given (unit)
+ * normal, leaving only the motion that runs along the wall.
+ *
+ *   vSlide = v - normal * dot(v, normal)
+ */
+export function slide(v: Vec, normal: Vec): Vec {
+	return sub(v, scale(normal, dot(v, normal)));
+}