On 2023-11-02 02:48, Dragan Simic wrote:
On 2023-11-02 06:48, Thomas Guyot wrote:
-c or --clear-screen ( and backward compat. -C or
--CLEAR-SCREEN )
Causes full screen repaints to be painted from the top
line down. By default, full screen repaints are done by scrolling
from the bottom of the screen.
AFAIK, the "-c" option is about the way screen contents is updated when
scrolled, and it exists to aid in resolving possible issues with some
terminal emulators. To make sure, I just tested it, and "-c" doesn't
replace "-X".
That's correct, you need both and also -y0
-yn or --max-forw-scroll=n
Specifies a maximum number of lines to scroll
forward. If it is necessary to scroll forward more than n lines, the
screen is repainted in‐
stead. The -c or -C option may be used to repaint from
the top of the screen if desired. By default, any forward movement
causes scrolling.
This option is, I'd guess, also about aiding in resolving possible
issues with some terminal emulators. Or maybe even with some actual
terminals as pieces of hardware, who knows, which may be too slow to
scroll many lines at once.
With a value of 0, it effectively redraw the screen on scroll. This
could have a potential impact on slow connections.
I actually have one major issue with it, it's that displaying anything
less than a full page will fill the screen with ~ on the bottom, just
like when scrolling up on a partial page without -F. I can see this
being a major annoyance when using for ex. git log -1, git show --stat
or --name-only, etc. as I usually do it to keep the latest history
within the current screen (and there's likely even commands that I
never seen using the pager because I never exceeded the page height).
Huh, this confuses me a bit, quite frankly. Isn't the "-F" option used
specifically to make pagination invisible in case fewer lines than one
full screen are displayed?
Indeed, but when less update from the bottom, it can add new lines and
let the overflow lines scroll up into the scrollback buffer.
Then updating it from the top, it draws the whole page, top to bottom.
That's fine for a full page but not desired for a partial one. Also note
that on my terminal (rxvt-unicode) when less clears the screen to draw
the first page the current screen is rolled up into scrollback - iirc
that's a configurable option, it would be worth testing other terminal's
behavior on that. IIRC it may also erase it when using the wrong termcap
file.
I haven't looked at the code, but I think it could be possibly to start
the -c behavior only after a full page is drawn, after exiting on
partial pages, which would give us the best of both worlds.
OTOH by repainting from the top, the scrollback buffer is never
affected. only the last displayed page remains on the terminal.
Just to clarify, it's the "-X" option that creates all the issues, and
the "--redraw-on-quit" option is already there to replace it with no
associated issues, but the trouble is that only newer versions of
less(1) support the "--redraw-on-quit" option. IOW, it's all about
improving less(1) to avoid complex workarounds required to handle
different versions, such as the workarounds used in bat(1).
TBH I haven't tested --redraw-on-quit, even on Debian Bookworm which was
just released a couple months ago this option isn't available. I suspect
that the issue isn't -X, but the scrolling behavior controlled by -y and
the full redraw controlled by -c.Actually I just tested my solution on
xfce4-terminal and it doesn't work, the terminal still push up stuff
above on redraw (noteworthy is with rxvt-unicode the first draw pushes
the current screen contents up but no other redraw does, which is what
makes it work so well - I haven't tried to find out what is being done
exactly... OTOH the redraw on scroll down is slightly noticeable there,
while impossible to see on xfce4-terminal. I'll install the latest less
and see what happens with --redraw on
If less could only enable this behavior after the first full page
draw, that would be perfect!
Could you, please, elaborate a bit on that?
I mentioned it slightly above, to be clear it would mean that:
1. less starts by just writing lined down as usual, making any lines
above scroll up and overflow into the scrollback buffer as usual
2. If less draws less than a page, exits as before - the effective
result is as if pager was cat
3. If less reaches a full page and still has lines to write, it turns on
-c's behavior and further updates happen from the top of the screen,
preventing scroll up (at least on rxvt-unicode)
Now, if all other terms misbehave here, that's an issue, making this
suggestion mostly useless. And considering the number of Windows users
we absolutely need to test Windows Terminal, and should probably test
MacOS's term too (whatever that is).
Dragan, that may be useful if you're discussing with less
developers...
We've basically reached some kind of an agreement about the need for a
good solution, which turned out to be rather complex as a result of
being quite universal and extensible, which was required for it to,
hopefully, be accepted into less(1). Also, the author of less(1) seems
to be quite busy with some other things, and he prefers to implement new
features himself.
We've also agreed on another new feature for less(1), hopefully, which
isn't exactly related, but should be quite useful. It's about the
secure mode for less(1).
Feel free to cc me on your next correspondence. If there are mailing
lists archives for the thread I'll fetch them as needed. We have at
least one working term/switch combination, which IMO is a better start
than nothing :)
Regards,
--
Thomas
