A layout measured while the surface is hidden is zero, and rescaling from it cannot recover

Fact

getBoundingClientRect() on an element inside a hidden or collapsed surface returns zeros — a background pane, a display:none ancestor, an embedded view that is not currently shown. The read succeeds; it is the box that is empty.

Anything derived from that measurement inherits the collapse. A canvas scene that sizes its world from the container gets sub-pixel cells, and every object placed in that world is stored at a coordinate that carries no information. When the surface reappears, the usual remedy — rescale the stored coordinates by the ratio of new size to old — cannot help: it multiplies noise by a large number.

Why it matters

The visible symptom appears long after the cause, in a surface that is now fully laid out, so it reads as a broken renderer rather than a stale measurement. Positions come back bunched into a band, or piled in one corner, and the code that produced them is correct for the size it was given.

It also hides in exactly the place work gets verified: a developer's window is always visible, while automated runs, backgrounded tabs and hidden panes are where the zero arrives.

How to apply

• Clamp the measurement to a usable floor rather than trusting it: width = Math.max(MIN, Math.round(rect.width)). A small sane world is recoverable by rescaling; a zero-sized one is not.
• Regenerate rather than rescale whenever the state is still disposable — before the user has interacted, a fresh layout fits the new shape far better than a stretched old one. Rescaling is for state that must be preserved.
• Store positions in units that survive a re-layout — grid cells, fractions of a container — so a resize changes only the conversion to pixels.
• The collapse reaches CSS too: in such a surface the viewport itself reports 0, so every vw/vh-derived custom property resolves to zero and any size built on it — font sizes included — disappears. Floor the token itself: --size: max(11rem, min(20rem, 78vw)).
• Recover automatically rather than measuring once: a ResizeObserver on the element fires as soon as it has a real box, which is the moment the surface becomes visible.