1460484 - Consider having out-of-flow frames contribute to the overflow area of their placeholder

Status: NEW

(Core :: Layout, enhancement, P2)

Description

[Matt Woodrow (:mattwoodrow)]

For display list purposes, we almost always want to know the overflow area of a given frame, including that of any placeholder descendants.

We currently have workarounds (nsDisplayListBuilder::MarkOutOfFlowFrameForDisplay), and bug 1453541 to deal with the current state.

We should consider trying to include the overflow area of OOF frames during reflow, as it would simplify display list code (but possible make other things more complicated).

Dbaron mentioned that the layout of OOFs can depend on the in-flow content, so we'd need to layout the normal content, layout the OOFs, and then do a post-processing pass to update the overflow areas of the normal content.

We also probably should do a full audit on the other (non-display list) consumers of overflow area, and see which they need.

Comment 1

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

The post-processing would be needed for absolutely-positioned frames, but floats could be handled in the primary pass.  I think there are a few other edge-cases of out-of-flows that would need to be considered.