Bug 257375

Created attachment 466505 [details] minimal repro of the issue When the visual viewport is scaled and moved a getBoundingClientRect does not include visualViewport.offsetLeft. In my minimal repro (attached and online https://www.katur.de/issues/safari_viewport-scaled_pos-fixed.html ) I check every second the BoundingClientRect of a base element and put its top,left value to the position of a position:fixed overlay element. This overlay element should cover the base element exactly. On desktop and mobile Chrome+Firefox this works even with pinch zoom. With mobile Safari I get an offset in the size of visualViewport.offsetLeft. The repo has a second overlay which uses the same BoundingClientRect values but add visualViewport.offsetTop/Left value to the position. With mobile Chrome+Firefox the "BCR overlay" is always over the base element even with pinch zoom. With mobile Safari the "BCR+offset* overlay" is always over the base element even with pinch zoom.