From 37c834d97584419c0ec800dd5b714b623811021a Mon Sep 17 00:00:00 2001
From: Tommaso Casaburi <tom@bitsocial.net>
Date: Mon, 16 Mar 2026 14:42:30 +0800
Subject: [PATCH] fix(reply-modal): keep drag interactions sharp (#1086)

---
 .../__tests__/reply-modal.test.tsx            | 28 +++++++++++++++++--
 .../reply-modal/reply-modal.module.css        |  3 --
 src/components/reply-modal/reply-modal.tsx    | 23 ++++++++-------
 3 files changed, 38 insertions(+), 16 deletions(-)

diff --git a/src/components/reply-modal/__tests__/reply-modal.test.tsx b/src/components/reply-modal/__tests__/reply-modal.test.tsx
index 0300a25b..7162b7ae 100644
--- a/src/components/reply-modal/__tests__/reply-modal.test.tsx
+++ b/src/components/reply-modal/__tests__/reply-modal.test.tsx
@@ -166,15 +166,26 @@ vi.mock('lodash/debounce', () => ({
 
 vi.mock('@react-spring/web', async () => {
   const React = await vi.importActual<typeof import('react')>('react');
+  const normalizeStyle = (style: Record<string, unknown> | undefined) =>
+    style
+      ? Object.fromEntries(
+          Object.entries(style).map(([key, value]) => [
+            key,
+            typeof value === 'object' && value !== null && 'get' in value && typeof (value as { get: unknown }).get === 'function'
+              ? (value as { get: () => unknown }).get()
+              : value,
+          ]),
+        )
+      : undefined;
 
   return {
     animated: {
-      div: React.forwardRef(({ style, ...props }: any, ref) => React.createElement('div', { ...props, ref, style: { touchAction: style?.touchAction } })),
+      div: React.forwardRef(({ style, ...props }: any, ref) => React.createElement('div', { ...props, ref, style: normalizeStyle(style) })),
     },
     useSpring: () => [
       {
-        x: { get: () => 120 },
-        y: { get: () => 80 },
+        left: { get: () => 120 },
+        top: { get: () => 80 },
       },
       {
         start: testState.springStartMock,
@@ -437,4 +448,15 @@ describe('ReplyModal', () => {
     expect(container.textContent).not.toContain('warning');
     expect(container.textContent).not.toContain('Spoiler?');
   });
+
+  it('positions the draggable modal with left/top styles instead of a transform layer', async () => {
+    await renderReplyModal('/mu/thread/post-1');
+
+    const modal = container.querySelector<HTMLDivElement>('[class*="container"]');
+
+    expect(modal?.style.left).toBe('120px');
+    expect(modal?.style.top).toBe('80px');
+    expect(modal?.style.transform).toBe('');
+    expect(modal?.style.touchAction).toBe('none');
+  });
 });
diff --git a/src/components/reply-modal/reply-modal.module.css b/src/components/reply-modal/reply-modal.module.css
index 8a7be92f..353b371c 100644
--- a/src/components/reply-modal/reply-modal.module.css
+++ b/src/components/reply-modal/reply-modal.module.css
@@ -8,9 +8,6 @@
   z-index: 999;
   background-color: var(--challenge-modal-background-color);
   border: var(--challenge-modal-border);
-  will-change: transform;
-  backface-visibility: hidden;
-  -webkit-backface-visibility: hidden;
 }
 
 .title {
diff --git a/src/components/reply-modal/reply-modal.tsx b/src/components/reply-modal/reply-modal.tsx
index 1f27a578..7b53b982 100644
--- a/src/components/reply-modal/reply-modal.tsx
+++ b/src/components/reply-modal/reply-modal.tsx
@@ -111,13 +111,16 @@ const ReplyModal = ({ closeModal, showReplyModal, parentCid, parentNumber, threa
   const nodeRef = useRef<HTMLDivElement>(null);
   const isMobile = useIsMobile();
 
-  const [{ x, y }, api] = useSpring(() => ({
-    x: window.innerWidth / 2 - 150,
-    y: window.innerHeight / 2 - 200,
+  const [{ left, top }, api] = useSpring(() => ({
+    left: Math.round(window.innerWidth / 2 - 150),
+    top: Math.round(window.innerHeight / 2 - 200),
   }));
 
   const bind = useDrag(
     ({ active, event, offset: [ox, oy] }) => {
+      const nextLeft = Math.round(ox);
+      const nextTop = Math.round(oy);
+
       if (active) {
         event.preventDefault();
         document.body.style.userSelect = 'none';
@@ -126,10 +129,10 @@ const ReplyModal = ({ closeModal, showReplyModal, parentCid, parentNumber, threa
         document.body.style.userSelect = '';
         document.body.style.webkitUserSelect = '';
       }
-      api.start({ x: ox, y: oy, immediate: true });
+      api.start({ left: nextLeft, top: nextTop, immediate: true });
     },
     {
-      from: () => [x.get(), y.get()],
+      from: () => [left.get(), top.get()],
       filterTaps: true,
       bounds: undefined,
     },
@@ -138,10 +141,10 @@ const ReplyModal = ({ closeModal, showReplyModal, parentCid, parentNumber, threa
   useEffect(() => {
     if (nodeRef.current && isMobile) {
       const viewportHeight = window.innerHeight;
-      const centeredPosition = scrollY + viewportHeight / 2 - 300;
-      api.start({ y: centeredPosition, immediate: true });
+      const centeredPosition = Math.round(scrollY + viewportHeight / 2 - 300);
+      api.start({ top: centeredPosition, immediate: true });
     }
-  }, [isMobile, scrollY, api]);
+  }, [api, isMobile, scrollY]);
 
   const parentCidRef = useRef<HTMLSpanElement>(null);
 
@@ -284,8 +287,8 @@ const ReplyModal = ({ closeModal, showReplyModal, parentCid, parentNumber, threa
       className={styles.container}
       ref={nodeRef}
       style={{
-        x,
-        y,
+        left,
+        top,
         touchAction: 'none',
       }}
     >