feat: add image viewer, carousel, and pan/zoom features

lib/momentum.ts

@@ -0,0 +1,70 @@
+export const THROW_MIN_DISTANCE = 14;
+export const THROW_GRACE_MS = 24;
+export const THROW_STALE_MS = 90;
+
+export function freshness(idleMs: number): number {
+  if (idleMs <= THROW_GRACE_MS) return 1;
+  return Math.max(0, 1 - (idleMs - THROW_GRACE_MS) / (THROW_STALE_MS - THROW_GRACE_MS));
+}
+
+export type Vec = { x: number; y: number };
+
+export function createVelocityTracker() {
+  let last: { x: number; y: number; t: number } | null = null;
+  let vx = 0;
+  let vy = 0;
+
+  return {
+    reset(x: number, y: number) {
+      last = { x, y, t: performance.now() };
+      vx = 0;
+      vy = 0;
+    },
+    sample(x: number, y: number) {
+      const now = performance.now();
+      if (last) {
+        const dt = now - last.t;
+        if (dt > 0) {
+          vx = vx * 0.7 + ((x - last.x) / dt) * 0.3;
+          vy = vy * 0.7 + ((y - last.y) / dt) * 0.3;
+        }
+      }
+      last = { x, y, t: now };
+    },
+    release(): Vec {
+      const idle = last ? performance.now() - last.t : Infinity;
+      const f = freshness(idle);
+      return { x: vx * f, y: vy * f };
+    },
+  };
+}
+
+export function runInertia(
+  velocity: Vec,
+  onStep: (dx: number, dy: number) => void,
+  opts: { minSpeed?: number; stopSpeed?: number; decayPerFrame?: number } = {},
+): () => void {
+  const minSpeed = opts.minSpeed ?? 0.04;
+  const stopSpeed = opts.stopSpeed ?? 0.012;
+  const decayPerFrame = opts.decayPerFrame ?? 0.94;
+  let { x: vx, y: vy } = velocity;
+  if (Math.hypot(vx, vy) < minSpeed) return () => { /* nothing started */ };
+
+  let raf = 0;
+  let last = performance.now();
+  const tick = (now: number) => {
+    const dt = Math.min(40, now - last);
+    last = now;
+    onStep(vx * dt, vy * dt);
+    const decay = Math.pow(decayPerFrame, dt / 16);
+    vx *= decay;
+    vy *= decay;
+    if (Math.hypot(vx, vy) > stopSpeed) {
+      raf = requestAnimationFrame(tick);
+    } else {
+      raf = 0;
+    }
+  };
+  raf = requestAnimationFrame(tick);
+  return () => { if (raf) cancelAnimationFrame(raf); };
+}