bug#57607: Feature request: Use the character cell on bottom-right corner of a terminal

[Akib Azmain Turja via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> Akib Azmain Turja <akib@disroot.org> writes:
>
>> Forwarding to bug-gnu-emacs list.
>>
>> Akib Azmain Turja <akib@disroot.org> writes:
>>
>>> Emacs never writes to the bottom-right corner of a terminal, because the
>>> terminal might open a new line at bottom of screen.  But terminals
>>> having any of 'ich', 'ich1' and 'smir' capabilities can write to the
>>> bottom-right corner of the terminal.  Almost all terminals have at least
>>> one of the aforementioned capabilities.  Why doesn't Emacs make use of
>>> that?
>
> I don't know.  And I don't know if that would work, it would require
> investigation.

There must be a way reliably way to do so, because ncurses can write to
the last character cell on terminal on linux console and xterm-like
terminal emulators.

>
> Emacs already writes to the bottom-right corner in case neither "am" nor
> "xn" are defined for the terminal in question.  vt100 and xterm, for
> instance, have "am" defined here, so Emacs doesn't write to the
> bottom-right corner.

I repeat: vt100 and xterm-like terminal having any of 'ich', 'ich1',
'il' and 'il1' or both 'smir' and 'rmir' can write to the last character
cell reliably without scrolling.

Here is what Emacs can do IMHO:

Glyph matrix (or whatever):

+------------------------+
|foo                     |
|bar                     |
|baz                     |
| --- *scratch* ---------|
|A very looooong message.|
+------------------------+

* Case: Any of 'ich', 'ich1', or both 'smir' and 'rmir' defined.

  *Note*: Won't work on displays with only a single column.

  Write to all character cells except the last two:

  +------------------------+
  |foo                     |
  |bar                     |
  |baz                     |
  | --- *scratch* ---------|
  |A very looooong messag  | <-- cursor
  +------------------------+
                         ^
                         |
                       cursor

  * Case: 'ich1' defined.

    Write the glyph to be placed on the last character cell.

    +------------------------+
    |foo                     |
    |bar                     |
    |baz                     |
    | --- *scratch* ---------|
    |A very looooong messag. | <-- cursor
    +------------------------+
                            ^
                            |
                          cursor

    Move to the character cell on the left side (cub1):

    +------------------------+
    |foo                     |
    |bar                     |
    |baz                     |
    | --- *scratch* ---------|
    |A very looooong messag. | <-- cursor
    +------------------------+
                           ^
                           |
                         cursor

    Invoke (or write or whatever) 'ich1':

    +------------------------+
    |foo                     |
    |bar                     |
    |baz                     |
    | --- *scratch* ---------|
    |A very looooong messag .| <-- cursor
    +------------------------+
                           ^
                           |
                         cursor

    Write the glyph to be placed on the character cell before the last
    character cell:

    +------------------------+
    |foo                     |
    |bar                     |
    |baz                     |
    | --- *scratch* ---------|
    |A very looooong message.| <-- cursor
    +------------------------+
                            ^
                            |
                          cursor

  * Case: 'ich' defined.

  Same as the 'ich1' case, but invoke 'ich' with parameter '1' instead
  of 'ich1'.

  * Case: 'smir' and 'rmir' defined.

    Write the glyph to be placed on the last character cell.

    +------------------------+
    |foo                     |
    |bar                     |
    |baz                     |
    | --- *scratch* ---------|
    |A very looooong messag. | <-- cursor
    +------------------------+
                            ^
                            |
                          cursor

    Move to the character cell on the left side (cub1):

    +------------------------+
    |foo                     |
    |bar                     |
    |baz                     |
    | --- *scratch* ---------|
    |A very looooong messag. | <-- cursor
    +------------------------+
                           ^
                           |
                         cursor

    Invoke 'smir'.

    Write the glyph to be placed on the character cell before the last
    character cell:

    +------------------------+
    |foo                     |
    |bar                     |
    |baz                     |
    | --- *scratch* ---------|
    |A very looooong message.| <-- cursor
    +------------------------+
                            ^
                            |
                          cursor

    Invoke 'rmir'.

* Case: 'il' or 'il1' defined.

  *Note*: Won't work on displays with only a single line.

  Write to all lines except the last two:

  +------------------------+
  |foo                     |
  |bar                     |
  |baz                     |
  |                        | <-- cursor
  |                        |
  +------------------------+
   ^
   |
  cursor

  Write the glyphs to be placed on the last line.

  +------------------------+
  |foo                     |
  |bar                     |
  |baz                     |
  |A very looooong message.|
  |                        | <-- cursor
  +------------------------+
   ^
   |
  cursor

  Move to the character cell above (cuu1):

  +------------------------+
  |foo                     |
  |bar                     |
  |baz                     |
  |A very looooong message.| <-- cursor
  |                        |
  +------------------------+
   ^
   |
  cursor

  * Case: 'il1' defined.

    Invoke 'il1'.

  * Case: 'il' defined.

    Invoke 'il1' with parameter '1'.

  +------------------------+
  |foo                     |
  |bar                     |
  |baz                     |
  |                        | <-- cursor
  |A very looooong message.|
  +------------------------+
   ^
   |
  cursor

  Insert the glyphs to be placed on the line before the last line:

  +------------------------+
  |foo                     |
  |bar                     |
  |baz                     |
  | --- *scratch* ---------|
  |A very looooong message.| <-- cursor
  +------------------------+
   ^
   |
  cursor

-- 
Akib Azmain Turja

Find me on Mastodon at @akib@hostux.social.

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