1507279 - Add an internal API for setting the visual viewport offset from the main thread

Status: RESOLVED FIXED

(Core :: Panning and Zooming, enhancement, P3)

Description

[Botond Ballo [:botond]]

Several internal consumers (e.g. session history, scroll anchoring) have a need to change the visual viewport offset from the main thread. This bug tracks adding an internal API for making such changes.

The API can live in nsIPresShell for C++ consumers, with an nsIDOMWindowUtils wrapper for JS consumers.

The implementation would send a message to APZ and update the RCD-RSF visual viewport offset, while leaving the layout viewport offset alone (modulo changes needed to keep the layout viewport enclosing the visual viewport).

Comment 1

[Botond Ballo [:botond]]

(In reply to Botond Ballo [:botond] from comment #0)
> The implementation would send a message to APZ and update the RCD-RSF visual
> viewport offset, while leaving the layout viewport offset alone (modulo
> changes needed to keep the layout viewport enclosing the visual viewport).

After thinking about this some more, I think it would make more sense to send the update as part of the next transaction, rather than having a separate message. We can add a "visual viewport offset updated" flag to ScrollMetadata, and have APZ accept both the layout and visual offsets sent by the main thread.

Comment 2

[Botond Ballo [:botond]]

Attachment: Bug 1507279 - Add a mechanism for the main thread to set a visual viewport offset. r=kats

Comment 3

[Botond Ballo [:botond]]

Attachment: Bug 1507279 - Expose the visual scrolling mechanism to internal JS users. r=kats

Depends on D16141

Comment 4

[Botond Ballo [:botond]]

I would have liked to avoid introducing FrameMetrics::mVisualViewportOffset, but that would have required some refactoring that I haven't done yet, and I didn't want to risk this not landing in 66 given all the things in blocks.

For an example use of the API, see this patch.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/bea2de966d14
Add a mechanism for the main thread to set a visual viewport offset. r=kats
https://hg.mozilla.org/integration/autoland/rev/47c259e23cfe
Expose the visual scrolling mechanism to internal JS users. r=kats

Comment 6

[Daniel Varga [:dvarga]]

https://hg.mozilla.org/mozilla-central/rev/bea2de966d14
https://hg.mozilla.org/mozilla-central/rev/47c259e23cfe