From 0b02f6579e4d0ce443f844f43fa718ac74bd77c5 Mon Sep 17 00:00:00 2001
From: Ovgodd <c.gromoff@gmail.com>
Date: Tue, 1 Sep 2026 09:07:10 +0200
Subject: [PATCH] =?UTF-8?q?fixup!=20=E2=99=BB=EF=B8=8F(frontend)=20refacto?=
 =?UTF-8?q?r=20screen=20share=20zoom=20pan=20with=20useMove=20and=20impera?=
 =?UTF-8?q?tive=20DOM=20updates?=
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---
 .../rooms/livekit/utils/screenShareZoom.ts       | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/src/frontend/src/features/rooms/livekit/utils/screenShareZoom.ts b/src/frontend/src/features/rooms/livekit/utils/screenShareZoom.ts
index 20fcb09e..51912642 100644
--- a/src/frontend/src/features/rooms/livekit/utils/screenShareZoom.ts
+++ b/src/frontend/src/features/rooms/livekit/utils/screenShareZoom.ts
@@ -2,7 +2,6 @@ export const MIN_ZOOM = 1
 export const MAX_ZOOM = 4
 export const ZOOM_STEP = 0.1
 export const WHEEL_ZOOM_SPEED = 0.002
-export const WHEEL_ZOOM_FOCUS_BLEND = 0.3
 export const PAN_STEP = 5
 export const PAN_CLAMP_HALF = 50
 
@@ -59,7 +58,10 @@ export const getCursorFromZoomState = (zoom: number, dragging: boolean) => {
   return dragging ? 'grabbing' : 'grab'
 }
 
-// Blend the current pan toward the cursor position so the zoom "tracks" the pointer.
+// Keep the content point under the cursor anchored while zooming. With
+// `scale(z) translate(pan%)`, a point at `offset` from the center renders at
+// `z * (offset + pan)`, so holding it still gives:
+// pan' = pan + cursor * (1 / zoom' - 1 / zoom).
 export const getWheelPanOffset = ({
   pan,
   prevZoom,
@@ -73,15 +75,11 @@ export const getWheelPanOffset = ({
   cursorXPercent: number
   cursorYPercent: number
 }): PanOffset => {
-  const zoomRatio = nextZoom / prevZoom
+  const panShift = 1 / nextZoom - 1 / prevZoom
   return clampPan(
     {
-      x:
-        pan.x +
-        (cursorXPercent - pan.x) * (1 - 1 / zoomRatio) * WHEEL_ZOOM_FOCUS_BLEND,
-      y:
-        pan.y +
-        (cursorYPercent - pan.y) * (1 - 1 / zoomRatio) * WHEEL_ZOOM_FOCUS_BLEND,
+      x: pan.x + cursorXPercent * panShift,
+      y: pan.y + cursorYPercent * panShift,
     },
     nextZoom
   )