[css-sizing] Is last remembered size logical or physical?

[Loirooriol]

Suppose an element stores a last remembered size with width/inline-size of 100px and height/block-size of 200px.
Then we add content-visibility: hidden so that the element uses that last remembered size.
Then we set writing-mode: vertical-lr.

What's the size of the element?

• width/block-size of 100px and height/inline-size of 200px (i.e. we stored width and height).
• height/inline-size of 100px and width/block-size of 200px. (i.e. we stored inline-size and block-size).

[Loirooriol]

Chromium remembers a logical size https://software.hixie.ch/utilities/js/live-dom-viewer/saved/10521

[Loirooriol]

ResizeObserver tracks changes in the logical sizes, so that seems the right approach.
Otherwise it would be hard to update a physical remembered size when a change in writing-mode preserves the logical size (so the ResizeObserver is not invoked) but swaps the physical size.

[css-meeting-bot]

The CSS Working Group just discussed [css-sizing] Is last remembered size logical or physical?, and agreed to the following:

• RESOLVED: Last remembered size is the logical size, not the physical size

The full IRC log of that discussion

<emeyer> Topic: [css-sizing] Is last remembered size logical or physical?
<emeyer> github: https://github.com//issues/7564
<emeyer> oriol: Spec says when c-i-s is auto, then we record current size, but doesn’t say how this is done and we stored height and width or block and inline size?
<emeyer> …I propose to store a logical size; Blink is already doing this, and I’m doing the same in Firefox
<TabAtkins> q+
<emeyer> …Approach seems better because observers are triggered on logical size change, not physical size
<emilio> ack TabAtkins
<Rossen_> ack TabAtkins
<emeyer> TabAtkins: This seems wild to me, I definitely imagine physical size when I wrote this, but given resizeobserver depends on logical size, let’s do it
<emeyer> RESOLVED: Last remembered size is the logical size, not the physical size