[Oberon] SystemV - Viewer Scroll

[Tomas Kral]

Joerg, Andreas,

> Forward scrolling: (single pass)
> Backward scrolling: second pass in forward direction.

Ah, this is the answer, then. Single (simpler) vs. double (more
complex).

The exercise is still worth doing, question is whether backward scroll
with its double pass will yield noticeably faster update in the end.

-- 
Tomas Kral <thomas.kral at email.cz>