flickering when scrolling

[LuanVSO]

when scrolling the text flickers, the whole buffer goes blank and is repainted. it's especially noticeable when trying to scroll up when the buffer is already at the top of the file.

https://user-images.githubusercontent.com/43626415/123591731-bf6ab200-d7c2-11eb-9f5b-0a0c57a9a8db.mp4