Created attachment 8617069 [details] parent – scrolling test case # Problem Scrolling an iframe inside a `preserve-3d` parent makes the the iframe disappear for 5+ seconds while a repaint occurs (even though "preserve-3d is NOT inherited"). # Steps to reproduce 1. Create a parent document with an iframe placed inside an element that has a style set of `transform-style: preserve-3d`. 2. Load the page in fullscreen + VR mode. 3. Notice how long it takes for the iframe to load (even when the document is served locally). 4. Scroll the iframe (either by directly manipulating `document.document.scrollTop` or `window.scrollTo` on the iframe's `contentWindow` or via JS that gets called from within the iframe). 5. Notice it takes at least 5 seconds for the iframe's document to be updated (the content actually disappears, but the iframe container remains). (I tried using the Dev Tools' profiler, but surprisingly nothing stood out.) # Test cases with an `<iframe>`: https://cvan.io/css-vr-slow-iframe-scrolling-tests/ with a `<div>`: https://cvan.io/css-vr-slow-iframe-scrolling-tests/div.html
This seems painfully slow; we do disable a bunch of clipping and partial updates that we'd normally do while scrolling, but we should investigate what's actually being painted here.
Webvr is no longer dependent on this, but this is still affecting non-webvr sites.
Whiteboard: [webvr] [horizon][css-vr]
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