Module scrollposition 

Where a scroll region is, and where an application is asking it to go.

Two halves of one gap. A scroll offset lives in the Runtime, written by the finger, the fling and the spring; until this module there was no way for an application to read one and no way to move one. So a “back to top” button, a chat that opens at its newest message, a bar that fades in as the page goes down and a list that loads more when its end comes into view were all inexpressible.

Neither half is a controller. The reference hands the application an object that owns the offset and is asked for it; here the offset belongs to the runtime, a view is rebuilt from state every frame, and an application speaks in messages. So the reading half is a notification — Widget::on_scroll, a message when the offset changes — and the commanding half is a request — ScrollTo, carried by a command and named by the same key a focus request uses.

Structs

ScrollPosition

Where a scroll region is, and how much room it has, at the moment it is reported.

ScrollTo

A request to move a scroll region, addressed to one axis or both.

Enums

ScrollTarget

One axis of a ScrollTo: an offset, or an end named rather than measured.