314946 2026-05-16 05:19:49 -0700 IntersectionObserver is broken at zooms outside 100% 2026-05-19 23:23:23 -0700 1 1 1 Unclassified WebKit Layout and Rendering Safari 26 Unspecified Unspecified NEW P2 Normal --- 1 alexander webkit-unassigned bfulgham kiet.ho simon.fraser zalan oldest_to_newest 2211411 0 alexander 2026-05-16 05:19:49 -0700 Steps to reproduce: 1. Have a container with children that are 100% in both height and width, i.e. match parents size EXACTLTY. 2. Add CSS scroll snap so that each child is not just the same size as parent, but also is match EXACTLY into frame regardless of scroll position. 3. Have IntersectionObserver at 1.0 threshold to monitor the current active slide. 4. Change zoom to something other than 100%. Actual results: IntersectionObserver stops triggering properly, you can see it in this super minimalistic carousel demo: https://codepen.io/waterplea/pen/XJjzrQW At, say 90% or 110% it stops working when swiping to the right, only to the left. Expected results: IntersectionObserver is triggered whenever a frame is snapped into place fully. 2211749 1 simon.fraser 2026-05-18 09:33:54 -0700 Alex, what OS/Safari version are you testing on? 2211762 2 alexander 2026-05-18 10:24:16 -0700 macOS 26.4.1 Safari Version 26.4 (21624.1.16.11.4) This actually happens for all browsers and OSes, it seems, I have filed an issue for FF and for Chrome it is already there for a few years. Not sure about Safari, but in Chrome those 90%/110% zoom causes elements to have subpixel sizes which causes IntersectionObserver to stop firing. 2212263 3 kiet.ho 2026-05-19 17:10:59 -0700 Alex, thank you for the bug report. When you say zoom, is this zooming by Cmd+/- or pinch zoom? 2212338 4 alexander 2026-05-19 23:23:23 -0700 By Cmd+/-, yes.