Re: [csswg-drafts] [css-view-transitions-2] Ignore offscreen elements from participating in transitions (#8282)

A quick summary of the main points to resolve here:

1. The primary purpose of the feature is to ignore names on elements which are offscreen, we need to decide which reference rectangles to use to define whether an element is offscreen. The proposed resolution is that an element is offscreen if its ink overflow rectangle doesn't intersect with the snapshot containing block. Given the resolution on https://github.com/w3c/csswg-drafts/issues/8649, ink overflow is sufficiently spec'd for this use-case.

2. The second question is about the syntax. From the options discussed above, `view-transition-visibility` seems like a good fit (it's kinda like `content-visibility`). The values being `visible` and `viewport`, where `viewport` means the element's `view-transition-name` is ignored if it's offscreen (as defined in 1 above).

3. The last question is what should be the default value for this property. The current behaviour is `visible` so changing it would come with a compat risk. That said, from a perf perspective `viewport` is better because it avoids rendering of offscreen content which most authors won't realize. If the group thinks this is the right thing to do, we can collect data on the usage to decide if the compat risk is acceptable.

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Received on Tuesday, 28 May 2024 14:08:14 UTC