Re: ***UNCHECKED*** RE: Strange behavior of Ncurses

[Thomas Dickey]

On Thu, Oct 17, 2024 at 01:18:48PM +0000, Urban Söderberg wrote:
> Hi Thomas & Branden,
> 
> We disabled the scrolling optimization using hashmaps, because we suspected 
> that was the reason behind messed up output. 
> So we rebuilt Ncurses with --disable-hashmap and that solved our problem, no 
> clr_eos is sent and no messy output observed.
> So we believe we found our way forward. Thanks a lot for your quick support!

hmm - the quickest thing to check would have been the padding.

What (actual) terminal device or program were you using?
 
> Best regards
> Urban
> 
> -----Original Message-----
> From: Thomas Dickey <dickey@his.com> 
> Sent: Thursday, 17 October 2024 02:43
> To: Urban Söderberg <Urban.Soderberg@knowit.se>
> Cc: Thomas Dickey <dickey@his.com>; G. Branden Robinson 
> <g.branden.robinson@gmail.com>; Ncurses Mailing List <bug-ncurses@gnu.org>; 
> Gustav W. Uppenberg <gustav.uppenberg@knowit.se>; Roxana Prelipceanu 
> <roxana.prelipceanu@knowit.se>; Pauline Littbrand 
> <pauline.littbrand@knowit.se>; Kristoffer Mattila 
> <kristoffer.mattila@knowit.se>
> Subject: Re: ***UNCHECKED*** RE: Strange behavior of Ncurses
> 
> On Wed, Oct 16, 2024 at 01:54:39PM +0000, Urban Söderberg wrote:
> > Hi Thomas & Branden,
> >  
> > We have activated trace in Ncurses.
> >  
> > Attached are two files:
> > space_trace_printout.zip
> > nr_trace_printout.zip
> > Unzip with password: 123456
> > Ncurses-functions used can be seen as well as $TERM.
> 
> I see - TERM=vt100, and 38400 baudrate.
> 
> As an aside, vt100 has padding (because it's for the real hardware terminal).
> If you're using a terminal emulator, you'll get some unwanted delays from 
> just that.  You can suppress the delays with the environment variable 
> NCURSES_NO_PADDING
> 
> In the vt100 entry, clear, cup, cuf1, ed, el, el1 all have time delays, and 
> if you're moving the cursor or clearing the screen a lot, that adds up:
> 
>       clear=\E[H\E[J$<50>, cr=\r, csr=\E[%i%p1%d;%p2%dr,
>       cub=\E[%p1%dD, cub1=^H, cud=\E[%p1%dB, cud1=\n,
>       cuf=\E[%p1%dC, cuf1=\E[C$<2>,
>       cup=\E[%i%p1%d;%p2%dH$<5>, cuu=\E[%p1%dA,
>       cuu1=\E[A$<2>, ed=\E[J$<50>, el=\E[K$<3>, el1=\E[1K$<3>,
> 
> Alternatively, if that's some real hardware, it may not scroll very well, and 
> _that_ could be the problem. :-)
> 
> These traces say the screensize is 69 by 185 (rather wide), and that ncurses 
> is initializing the terminal to scroll the whole screen.
> The initialization didn't show in the earlier examples.
>   
> > First one, space_trace_printout, is covering the printout which we have 
> > issues with, where we see the clear to end of screen escape sequence, move 
> > cursor to first line,  followed by a lot of scrap text.
> > This trace-log is also bigger than the other one.
> >  
> > Second one, nr_trace_printout, no issue is seen, each line starting with a 
> > number, making each line unique.
> >  
> > A look at space_trace_printout:
> > Hard to us to interpret entries, but we noticed something, 
> > nc_scroll_optimize (at line: 67364):
> > .
> > .
> > newscr[65]  30 31 ='                             46   '
> > newscr[66]  16 31 ='                PRC-610      229  '
> > newscr[67]  16 31 ='                             423  '
> > newscr[68]  29 31 ='                                  '
> > + + + + called {_nc_signal_handler(0)
> > + + + + return }
> > + + + + called {_nc_scroll_optimize(0x17fb4f0)
> > virt  -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 
> > -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 
> > -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 
> > -1 -1
> > + + + + return }
> > GoTo(0x17fb4f0, 68, 0) from (68, 184)
> > + + + + called {_nc_tinfo_mvcur(0x17fb4f0,68,184,68,0)
> > + + + + + called {tparm("\e[%i%p1%d;%p2%dH$<5>", 68, 0) return 
> > + + + + + }"\e[69;1H$<5>"
> > + + + + + called {tparm("\e[%p1%dD", 184) return }"\e[184D"
> > + + + + + called {tparm("\e[%p1%dB", 68) return }"\e[68B"
> > tputs(mvcur = "\r", 1, _nc_outch) called
> > + + + + return }0
> > tputs(clr_eos = "\e[J$<50>", 1, _nc_outch) called Transforming lines, 
> > nonempty 68
> > + + + + called {TransformLine(0x17fb4f0, 0)
> > GoTo(0x17fb4f0, 0, 16) from (68, 0)
> > + + + + + called {_nc_tinfo_mvcur(0x17fb4f0,68,0,0,16)
> > + + + + + + called {tparm("\e[%i%p1%d;%p2%dH$<5>", 0, 16) return 
> > + + + + + + }"\e[1;17H$<5>"
> > tputs(mvcur = "\e[1;17H$<5>", 1, _nc_outch) called
> > + + + + + return }0
> > PutRange(0x17fb4f0, 0x1815310, 0x17ffd60, 0, 16, 31) EmitRange 
> > 7:{"PRC-610"} PutAttrChar({'P' = 0120}) at (0, 16) PutAttrChar({'R' = 
> > 0122}) at (0, 17) PutAttrChar({'C' = 0103}) at (0, 18) 
> > PutAttrChar({'-' = 055}) at (0, 19) .
> > .
> > 
> > Compare this to the trace where the same text is printed, but 
> > nc_scroll_optimize (at line:  67041) behaves differently:
> > .
> > . 
> > newscr[65]   0 32 ='0                             46   '
> > newscr[66]   0 32 ='1                PRC-610      229  '
> > newscr[67]   0 32 ='2                             423  '
> > newscr[68]   0 32 ='                                   '
> > + + + + called {_nc_signal_handler(0)
> > + + + + return }
> > + + + + called {_nc_scroll_optimize(0x1fbf4f0)
> > new line 2 is hash-identical to old line 3 (unique) new line 5 is 
> > hash-identical to old line 6 (unique) new line 8 is hash-identical to 
> > old line 9 (unique) new line 11 is hash-identical to old line 12 
> > (unique) new line 14 is hash-identical to old line 15 (unique) new 
> > line 17 is hash-identical to old line 18 (unique) new line 20 is 
> > hash-identical to old line 21 (unique) new line 23 is hash-identical 
> > to old line 24 (unique) new line 26 is hash-identical to old line 27 
> > (unique) new line 29 is hash-identical to old line 30 (unique) new 
> > line 32 is hash-identical to old line 33 (unique) new line 35 is 
> > hash-identical to old line 36 (unique) new line 38 is hash-identical 
> > to old line 39 (unique) new line 41 is hash-identical to old line 42 
> > (unique) new line 44 is hash-identical to old line 45 (unique) new 
> > line 47 is hash-identical to old line 48 (unique) new line 50 is 
> > hash-identical to old line 51 (unique) new line 53 is hash-identical 
> > to old line 54 (unique) new line 56 is hash-identical to old line 57 
> > (unique) new line 59 is hash-identical to old line 60 (unique) new 
> > line 62 is hash-identical to old line 63 (unique) new line 65 is 
> > hash-identical to old line 66 (unique) connected new line 1 to old 
> > line 2 (backward continuation) connected new line 0 to old line 1 
> > (backward continuation) connected new line 3 to old line 4 (forward 
> > continuation) connected new line 4 to old line 5 (backward 
> > continuation) connected new line 6 to old line 7 (forward 
> > continuation) connected new line 7 to old line 8 (backward 
> > continuation) .
> > .
> >  
> > Why does _nc_scroll_optimize behave differently in those cases? We would 
> > expect it to behave the same.
> > Is this normal behavior? Can this optimization be disabled, or is it 
> > something we can do/configure to avoid this behavior?
> 
> The scrolling optimization compares the whole line, because (it usually 
> works) vt100-style scrolling regions affect the whole line.  Lines with 
> numbers are going to look different -- and it'll cause ncurses to give up on 
> that faster than the other example.
> 
> The space_trace_printout example says that it's calling the optimization 
> function 275 times because wrefresh is called that many times, and _that_ 
> happens after adding a newline (causing the scrolling).  The trace seems to 
> show that it's recognizing that the lines shift by one - okay.
> 
> You asked about the backspaces - I see an example in this chunk, which says 
> that it's updating a line partially by jumping from
> 1,32 to 2,29, and the relevant capability is cursor_left (which in the vt100 
> entry happens to be a backspace because it's shorter than \E[D (1 byte vs 3)
> 
>       {TransformLine(0x17fb4f0, 2)
>       GoTo(0x17fb4f0, 2, 29) from (1, 32)
>       + + + + + called {_nc_tinfo_mvcur(0x17fb4f0,1,32,2,29)
>       + + + + + + called {tparm("\e[%i%p1%d;%p2%dH$<5>", 2, 29)
>       + + + + + + return }"\e[3;30H$<5>"
>       + + + + + + called {tparm("\e[%p1%dB", 1)
>       + + + + + + return }"\e[1B"
>       + + + + + + called {tparm("\e[%p1%dD", 3)
>       + + + + + + return }"\e[3D"
>       + + + + + + called {tparm("\e[%p1%dB", 1)
>       + + + + + + return }"\e[1B"
>       + + + + + + called {tparm("\e[%p1%dC", 29)
>       + + + + + + return }"\e[29C"
>       + + + + + + called {tparm("\e[%p1%dB", 2)
>       + + + + + + return }"\e[2B"
>       + + + + + + called {tparm("\e[%p1%dC", 29)
>       + + + + + + return }"\e[29C"
>       + + + + + + called {tparm("\e[%p1%dB", 1)
>       + + + + + + return }"\e[1B"
>       + + + + + + called {tparm("\e[%p1%dD", 3)
>       + + + + + + return }"\e[3D"
>       tputs(mvcur = "\n\b\b\b", 1, _nc_outch) called
>       + + + + + return }0
>       PutRange(0x17fb4f0, 0x18158f0, 0x18089e0, 2, 29, 31)
>       EmitRange 3:{"2  "}
>       PutAttrChar({'2' = 062}) at (2, 29)
>       PutAttrChar({' ' = 040}) at (2, 30)
>       PutAttrChar({' ' = 040}) at (2, 31)
>       + + + + return }
> 
> But determining whether you need the padding is easier than determining if 
> that terminal is inefficient with scrolling or partial line updates :-)
>   
> > Best regards
> > Urban
> > 
> > -----Original Message-----
> > From: Thomas Dickey <dickey@his.com>
> > Sent: Saturday, 12 October 2024 15:53
> > To: G. Branden Robinson <g.branden.robinson@gmail.com>
> > Cc: Urban Söderberg <Urban.Soderberg@knowit.se>; Ncurses Mailing List 
> > <bug-ncurses@gnu.org>; Gustav W. Uppenberg 
> > <gustav.uppenberg@knowit.se>; Roxana Prelipceanu 
> > <roxana.prelipceanu@knowit.se>; Pauline Littbrand 
> > <pauline.littbrand@knowit.se>; Kristoffer Mattila 
> > <kristoffer.mattila@knowit.se>
> > Subject: Re: Strange behavior of Ncurses
> > 
> > [Du får inte e-post ofta från dickey@his.com. Läs om varför det här är 
> > viktigt på https://aka.ms/LearnAboutSenderIdentification ]
> > 
> > ----- Original Message -----
> > | From: "G. Branden Robinson" <g.branden.robinson@gmail.com>
> > | To: "Urban Söderberg" <Urban.Soderberg@knowit.se>
> > | Cc: "Thomas Dickey" <dickey@his.com>, "Ncurses Mailing List" 
> > <bug-ncurses@gnu.org>, "Gustav W. Uppenberg"
> > | <gustav.uppenberg@knowit.se>, "Roxana Prelipceanu" 
> > <roxana.prelipceanu@knowit.se>, "Pauline Littbrand"
> > | <pauline.littbrand@knowit.se>, "Kristoffer Mattila" 
> > | <kristoffer.mattila@knowit.se>
> > | Sent: Friday, October 11, 2024 2:11:02 PM
> > | Subject: Re: Strange behavior of Ncurses
> > 
> > | At 2024-10-11T13:18:16+0000, Urban Söderberg wrote:
> > |> We did strace on our application and could see that character 
> > |> sequences are caused by ncurses.
> > |>
> > |> File: dev-pts-2-trace3.log
> > |> Printout lines starting with spaces.
> > |> We can see several lines like this:
> > |> [pid 2001732] 12:04:54.106158 write(1</dev/pts/2<char 136:2>>, 
> > |> "\33[J\33[1;17H",
> > |> 10) = 10 <0.000015>
> > |> This causes issues.
> > |
> > | Just FYI, the sequence in question,
> > |
> > | \33[J
> > |
> > | looks like "CSI J", the ECMA-48 escape sequence for clearing the 
> > | screen, [1] and
> > |
> > | \33[1;17H
> > |
> > | looks like "CSI H", the ECMA-48 escape sequence for (absolute) 
> > | cursor positioning ("CUP").
> > |
> > | A copy of ECMA-48 can be found here:
> > |
> > | https://www.ecma-international.org/wp-content/uploads/ECMA-48_5th_ed
> > | it
> > | ion_june_1991.pdf
> > |
> > | If ncurses is emitting those sequences, it is likely because the 
> > | terminfo database entry for the value of $TERM on the system records 
> > | that they are how to manifest the operations in question.
> > 
> > Actually, ncurses could emit those strings, but because ncurses optimizes 
> > cursor movement, the only way it would be sending the cursor to the right 
> > margin and _then_ going to the next line would be if the application were 
> > forcing the screen to be updated and causing ncurses to wait for keyboard 
> > input.  That's kind of unlikely.
> > 
> > It's a lot more likely that the application is a low-level terminfo or 
> > termcap application which does no optimization.  If the application is 
> > stripped and statically linked, it would take some work to prove this, but 
> > if it's not, then someone could use "nm" to list the functions it uses.
> > 
> > If it's using initscr or newterm, that says it could be using cursor 
> > optimization.
> > It's still possible that the developer bypasses all of that (think 
> > "printf"...).
> > 
> > strace won't tell me any of that.  "nm" or "nm -D" is the way to start 
> > collecting data.
> > 
> > |
> > | Is your $TERM correct?
> > |
> > | Regards,
> > | Branden
> > |
> > | [1] ECMA-48 calls it "ERASE IN PAGE"; the ctlseqs.ms document calls it
> > |     "Erase in Display".  Both abbreviate it as "ED".
> > 
> > --
> > Thomas E. Dickey <dickey@invisible-island.net> 
> > https://invisible-island.net
> > 
> 
> 
> 
> 
> --
> Thomas E. Dickey <dickey@invisible-island.net> https://invisible-island.net

-- 
Thomas E. Dickey <dickey@invisible-island.net>
https://invisible-island.net

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