Understanding Updating World Coordinate

[TheMachineHere]

Hi,

I'm fairly new to ARCore and OpenGL.
This app is great and similar to what i'm trying to do.

I don't understand how the coordinates are updated for each stroke in this app after you move around. I know LineUtils.GetWorldCoords gets you world coordinate from screen touch, but how do we keep track of that and keep updating them?

Any help would be very appreciated.

Thanks,