801923 - nsDisplayListBuilder::IsFixedItem is broken

Status: NEW

(Core :: Layout, defect)

Description

[Jonathan Watt [:jwatt]]

It seems like nsDisplayListBuilder::IsFixedItem is a bit broken. It bases its return value on whether nsLayoutUtils::IsScrolledByRootContentDocumentDisplayportScrolling returns false. However, on non-Mobile it will _always_ return false, since it calls nsLayoutUtils::GetDisplayPort(), which Matt tells me will always return null for non-Mobile.

Comment 1

[Robert O'Callahan (:roc) (email my personal email if necessary)]

That's OK. Display items are fixed from the point of view of the off-main-thread-compositor ... which there isn't one, on desktop (and if there was one, we'd be setting a display port!)