[Line UI] Bug with handle movement when page has scrolled.

[atomworks]

Overview

When scrolling a page with the UI line drawing tool the handles become Y-offset against the mouse position when dragging a handle.

I'm sure we've fixed this bug before so I'm not sure why it's back on this project. The project using this is using 1.5.4 but since then it seems no code has change in the LineUI. There is a slight chance this is due to some implementation on the project side as they are toggling between a read-only and dragging variation but it's best to investigate and confirm this in isolation first as I expect it's most likely an issue on the UI Kit side.

Investigation

Looking at this issue it's a bug where by when the body scrolls it changes the co-ordinates being reported causing handles to become detached. It seems that many of our use cases currently have their own divs that scroll internally for this view and so the body doesn't actually move, so previously we may have used this behaviour as a fix. However, it's something we should fix on the UI Kit side.

How to recreate.

Just add a basic line drawing instance to an empty page and wrap it in a container with a fixed height of 200vh (for example). Then you can scroll and recreate this behaviour.

[atomworks]

I just test this thinking we fixed it a long time ago and it's still an issue. We might want to address this one sooner, perhaps while reviewing the component.

Some of the newer patterns planned will need this to work.