The default behaviour for View Transitions when capturing the image of an element is to paint its entire ink overflow rectangle. But there are cases where this is not possible. A common one is the element exceeding max texture size supported by the hardware on that device. It can technically be done (by tiling the image) but is complicated. It's also likely we'll hit cases where painting the whole element will have significant memory overhead and clipping the snapshot makes sense.

We want the snapshot to include at least the intersection of the element's ink overflow rectangle and the snapshot root (a.k.a the visible viewport). Other than that, it's unclear how prescriptive the spec needs to be here.

• The spec could recommend that for the area outside the visible viewport, or if the whole element is outside the viewport, the implementation should capture the subset closest to the viewport.
• The snapshot should be at least as big as the snapshot root.

This issue is tracked here in the spec.