[css-view-transitions-1] UA CSS should add transform-origin to view-transition-group

[khushalsagar]

The UA CSS should have the following rule on view-transition-group:

transform-origin: top left;

This is because the dynamic transform computed here should be with respect to the top left corner of the element. Given that the element's bounds will also animate during the transition, it makes sense.

[astearns]

I’d like to see at least one other person agree to the proposed resolution here before trying the async route. What happens when authors override the UA default? Are there no writing mode or direction concerns with a top left default?

[khushalsagar]

What happens when authors override the UA default? Are there no writing mode or direction concerns with a top left default?

Devs changing the UA default would lead to unpredictable behaviour no matter what the default is. Since the transform value computed by the UA for the group will assume a particular value for transform-origin. The writing mode/direction is a good point. Its not intuitive for the transform to be relative to the top-left corner for RTL writing mode.

I'm going to close this issue then. The current spec uses the default value of transform-origin which is relative to the center of the box. That makes most sense in that it is immune to writing mode/direction.