fix: add delta

app/util/delta.js

@@ -0,0 +1,32 @@
+import TickingPromise from '@/util/ticking-promise.js';
+
+export default function delta(object, properties) {
+  const deltas = {};
+  for (const key in properties) {
+    const property = properties[key];
+    const delta = {
+      duration: Infinity,
+      elapsed: 0,
+      ...property,
+    };
+    deltas[key] = delta;
+  }
+  let stop;
+  const promise = new TickingPromise(
+    (resolve) => {
+      stop = resolve;
+    },
+    (elapsed, resolve) => {
+      for (const key in deltas) {
+        deltas[key].elapsed += elapsed;
+        if (deltas[key].elapsed >= deltas[key].duration) {
+          object[key] += deltas[key].delta * (deltas[key].duration - deltas[key].elapsed);
+          resolve();
+          return;
+        }
+        object[key] += deltas[key].delta * elapsed;
+      }
+    },
+  );
+  return {stop, deltas, promise};
+}