1780320 - Support child scroll roots if in the root coordinate system

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, task)

Comment 1

[Glenn Watson [:gw]]

Attachment: Bug 1780320 - Support child scroll roots if in the root coordinate system

A requirement of calling get_relative_transform is that the child
node is an ancestor of the reference node. To ensure this invariant
is met, we exclude non-ancestor scroll roots from consideration when
picking a scroll root for an atomic picture cache slice. However, this
can mean we select a non-optimal scroll root in some cases. But the
get_relative_transform constraint only applies if the spatial nodes
are in a different coordinate system - if we know that the scroll roots
are in the same coordinate system, we can always calculate the correct
relative transform, regardless of ancestry of the nodes. We can rely on
this to relax the condition here, which means we select a more appropriate
scroll root, resulting in much less invalidation and rasterization work
in these cases.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/d6c85070b665
Support child scroll roots if in the root coordinate system r=gfx-reviewers,lsalzman

Comment 3

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/d6c85070b665