New approach: observe how the where the cursor went.

calculate vertical the cursor and window diffs

One line taller:

if cursor moves down a line:

move everything down a line

scroll_offset -= 1

top_usable_line += 1

if cursor stays:

everything stays

One line shorter:

if cursor moves up a line:

move everything up a line

scroll_offset += 1

top_usable_line -= 1 if top_usable_line > 0

if cursor stays:

everything stays

To make terminal one line taller:

if there is another line of history to show, show that and move everything down a li.

Top usable line goes visually down by one (+=1). Scroll offset -= 1

CURSOR MOVES DOWN

if there are no more lines of history

if there is junk space at the bottom, absorb it.

Top usable line, scroll offset remain the same

if cursor is on bottom line, move everything up a line

Top usable line goes up one. Scroll offset goes up one

To make terminal one line shorter:

if there is at least one line of history offscreen,

move everything up one line. Top usable line moves up (-= 1) (while > 0)

Scroll offset += 1

if there is no history offscreen

if there is empty space at the bottom,

remove empty space at bottom. Top usable line, scroll offset are the same

if there is no empty space (cursor is at bottom), move up one line.

Top usable line moves up by one, -= 1

scroll offset += 1,

if cursor is on top line? (seems to depend on terminal emulator)

Note: We should probably kill the completion box during resizes, because real terminal

is based on where the cursor is

Note: How does terminal wrapping work? It doesn't change the height

when a line wraps around, so how does addressing even work?

How to make a terminal one

Note: Terminal.app adds a line and puts cursor at bottom when scroll up.

Current bug: when window change brings pre-bpython history into visibility, problems