RE: Slow redisplay with long lines

[Stephan Mueller]

From: Eli Zaretskii [mailto:address@hidden 
" > From: Stephan Mueller <address@hidden>
" > " > Long lines slow down redisplay because it needs to scan the entire
" > " > line to see how tall it will be on display.
" > "
" > " Why should it care about the whole line rather than only the part
" > " of it that's displayed?
" > 
" > So that the line height doesn't change when scrolling horizontally
" > and a taller character comes into view?
"
" No, horizontal scrolling causes another redisplay, which examines the
" characters that came into view at that time.

So, IIUC, that means that scrolling horizontally _can_ cause the user's
experience to be that the height of a line was changed by looking at a
different portion of it.  Understood it is redisplayed (and so no doubt
draws correctly), but I'd still consider the height change to be an odd
behaviour.  I'm curious if it was an intentional choice (perhaps in the
name of perf, removing one of the reasons to scan the whole line)?
 
stephan($0.02);