PullDownToRefresh: rewrite spring animation

- fix #12

src/timelines/PullDownToRefresh.tsx

@@ -46,41 +46,56 @@ const PullDownToRefresh: Component<{
   let lts = -1;
   let ds = 0;
   let holding = false;
-  const M = 1;
-  const K = -10;
-  const D = -10;
+  const K = 5;
   const updatePullDown = (ts: number) => {
     released = false;
     try {
       const x = untrack(pullDown);
       const dt = lts !== -1 ? ts - lts : 1 / 60;
-      const fs = (ds / Math.pow(dt, 2)) * M;
-      const fh = (x + ds) * K + D * v;
-      const f = fs + fh;
-      const a = f / M;
-      v += a * dt;
-      if (holding && v < 0) {
-        v = 0
-      }
+      const vspring = holding ? 0 : K * x * dt;
+      v = ds / dt - vspring;
+
       setPullDown(x + v * dt);
+
       if (Math.abs(x) > 1 || Math.abs(v) > 1) {
         requestAnimationFrame(updatePullDown);
       } else {
         v = 0;
         lts = -1;
       }
-      if (!holding && untrack(pullDownDistance) >= 160 && !props.loading && props.onRefresh) {
-        setTimeout(props.onRefresh, 0)
+
+      if (
+        !holding &&
+        untrack(pullDownDistance) >= 160 &&
+        !props.loading &&
+        props.onRefresh
+      ) {
+        setTimeout(props.onRefresh, 0);
+        // FIXME: this may trigger at multiple frames
       }
     } finally {
       ds = 0;
       released = true;
     }
   };
+
+  let wheelTimeout: ReturnType<typeof setTimeout> | undefined;
+
+  const onWheelNotUpdated = () => {
+    wheelTimeout = undefined;
+    holding = false;
+  };
+
   const handleLinkedWheel = (event: WheelEvent) => {
     const scrollTop = (event.target as HTMLElement).scrollTop;
     if (scrollTop >= 0 && scrollTop < 1) {
-      ds = -(event.deltaY / window.devicePixelRatio / 4);
+      event.preventDefault()
+      ds = -(event.deltaY / window.devicePixelRatio / 2);
+      holding = true;
+      if (wheelTimeout) {
+        clearTimeout(wheelTimeout);
+      }
+      wheelTimeout = setTimeout(onWheelNotUpdated, 200);
       if (released) {
         released = false;
         requestAnimationFrame(updatePullDown);
@@ -107,6 +122,7 @@ const PullDownToRefresh: Component<{
       return;
     }
     const item = event.targetTouches.item(0)!;
+    event.preventDefault();
     if (lastTouchId && item.identifier !== lastTouchId) {
       lastTouchId = undefined;
       lastTouchScreenY = 0;
@@ -114,7 +130,7 @@ const PullDownToRefresh: Component<{
     }
     holding = true;
     if (lastTouchScreenY !== 0) {
-      ds = item.screenY - lastTouchScreenY;
+      ds = (item.screenY - lastTouchScreenY) / window.devicePixelRatio;
     }
     lastTouchScreenY = item.screenY;
     if (released) {