1924130 - Optionally skip rendering a snapshotted picture

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, task, P3)

Description

[Nicolas Silva [:nical]]

For the live capture of the new-state, the view-transition spec requires that the capture be rendered "as if it was an image". The plan is to use an actual Image display item for it.

To render the live snapshot as an image in the same frame it is captured (since it is live), we have to prevent the capturing step from actually drawing into the parent so that only the image item will. Conveniently, the spec also wants the live capture to be snatched into the front layer so this should help.

Note: I bet that we will eventually come to regret the resulting API. It's really odd and surprising to have something at an arbitrary place in the display list that is rendered but not composited, so that something elsewhere in the display list can render it. The better long term solution would be to extract these stacking contexts from the flow of the DL by either making them separate pipelines or explicitly having multiple roots in the DL/frame (internally that's what webrender will probably have to do to manage the snapshots).
However the way this weird API seems to perfectly sit in between the quirks of how the spec and and display list building want to operate.

Comment 1

[Nicolas Silva [:nical]]

Attachment: Bug 1924130 - Add support for detached stacking contexts. r=#gfx-reviewers

A dettached stacking context is cached into a snapshot image but not drawn into the frame.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/443287b84688
Add support for detached stacking contexts. r=gfx-reviewers,gw

Comment 3

[amarc]

https://hg.mozilla.org/mozilla-central/rev/443287b84688