tig window flickers

[jirislaby]

Very often, it happens that the tig window flickers or show half screen old+half screen new content. This happens especially when paging (pg-up, pg-down) through history or patch.
If I run for example this in the linux kernel:

tig v5.16-rc1..v5.16

I see this:

Then, if I navigate through it, I see:
https://user-images.githubusercontent.com/530775/151510043-2aab187f-516c-46f4-9b89-1495e4d02a03.mp4

I don't know if this is tig's, curses, compositor (plasma on wayland), or gfx driver (i915 -- KMS) issue. However, I don't see it with any other app (incl. kernel's menuconfig, vim, less -- the latter two seem to use only tinfo, not curses).

[koutcher]

Have you tried with a different terminal emulator ?

[jirislaby]

@koutcher right, happens only in xterm which I use. In, konsole, does not reproduce.

[koutcher]

@jirislaby, the flickering on your video looks a bit like some double-buffer artefact, maybe you can confirm with strace if tig is doing something while it happens. Tig is using some optimisation tricks (see init_display() in src/display.c), you could try to unset XTERM_VERSION and try with TERM_PROGRAM set either to gnome-terminal or Apple_Terminal to see if one helps.

[jirislaby]

Wow:

unset XTERM_VERSION
export TERM_PROGRAM=gnome-terminal
tig v5.16-rc1..v5.16

The issue is gone, the same as with:

unset XTERM_VERSION
export TERM_PROGRAM=Apple_Terminal
tig v5.16-rc1..v5.16

For confirmation, the issue is back with:

export XTERM_VERSION='XTerm(370)'
tig v5.16-rc1..v5.16

So it's use_scroll_redrawwin causing issues if I got it right:

tig/src/display.c

Lines 695 to 723 in 7218788

	term = getenv("XTERM_VERSION")
	? NULL
	: (getenv("TERM_PROGRAM") ? getenv("TERM_PROGRAM") : getenv("COLORTERM"));
	if (term && !strcmp(term, "gnome-terminal")) {
	/* In the gnome-terminal-emulator, the warning message
	* shown when scrolling up one line while the cursor is
	* on the first line followed by scrolling down one line
	* corrupts the status line. This is fixed by calling
	* wclear. */
	use_scroll_status_wclear = true;
	use_scroll_redrawwin = false;
	} else if (term &&
	(!strcmp(term, "xrvt-xpm") || !strcmp(term, "Apple_Terminal") ||
	!strcmp(term, "iTerm.app"))) {
	/* No problems with full optimizations in
	* xrvt-(unicode)
	* aterm
	* Terminal.app
	* iTerm2 */
	use_scroll_status_wclear = use_scroll_redrawwin = false;
	} else {
	/* When scrolling in (u)xterm the last line in the
	* scrolling direction will update slowly. This is
	* the conservative default. */
	use_scroll_redrawwin = true;
	use_scroll_status_wclear = false;
	}

[jirislaby]

It's also slightly problematic over ssh. XTERM_VERSION is not sent by default. Only these are (TERM is documented in ssh's man):

$ env|grep TERM
COLORTERM=1
TERM=xterm-256color

So the detection above doesn't work there too.

[koutcher]

I tried to reproduce the original issues with xterm and gnome-terminal on a venerable RHEL 4 and couldn't succeed, so I think it is not unreasonable to believe we can now remove these hacks safely.