Klaus-Peter Wegge <[email protected]> writes:
> Hello,
> with my update to debian 8 I also updated from brltty3.8 to 5.2.
> Now I'm approaching the following problem when using alpine2.11:
> When reading a mail by moving the braille window around
> the braille window jumps back to the current cursor position all approx.
> 5 seconds. Alpine is configured for -show-cursor.
> I know that freezing the screen may be an option but that's
> not very comfortable.
> This effect does not appear when login in by ssh from an old PC with
> brtlly 4.x.
> The described behavior appears only in alpine.
> Any ideas or hints?
>From the point of view of modern hardware, networking and BRLTTY, ttys
have a design flaw. It is imopssible to write text to a terminal without
moving the cursor (except in some weird cases, see ncurses's leaveok function,
which does not work for example on the Linux console).
Therefore when BRLTTY is reading the screen, and it happens to do so while
some program is writing on the corresponding terminal device, BRLTTY notices
that the cursor has moved to a new location in which case cursor tracking
kicks in.
Therefore it is at the moment almost impossible to use cursor tracking in
programs which update the screen frequently. I, for example, would like to
have emacs display a clock on its mode line, but I cannot activate the
feature, because it causes frequent screen updates and lots of unwanted cursor
tracking.
This could be worked around in BRLTTY perhaps if it could delay cursor
tracking by few milliseconds. This would actually be great, IMHO.
It could work like this:
1. In normal screen update handling routine:
- If cursor has moved, make a note of it
2. If cursor was moved in last screen update, make a cursor position check
one ms after the screen update:
- If cursor did not move, apply cursor tracking and continue normally
- If it did move, restart step 2 unless it is time to do a whole screen
update
(I actually don't know how BRLTTY does screen update handling, so my idea
might need quite a bit of adaptation.)
--
Aura
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