[BRLTTY] ‘empty console’

[Nicolas Pitre]

On Thu, 28 Nov 2019, Sebastian Humenda wrote:
> Nicolas Pitre schrieb am Wed, Nov 27, 2019 at 12:38:29PM -0500:
> > On the BRLTTY's side, there could possibly be a way to use TIOCGWINSZ on
> > the console device when vcsa returns 255 on the screen dimension. But
> > that won't help with cursor position beyond 255 though. At least the
> > user could then be warned.
> 
> How do other applications work around this limitation? E.g. Tmux? Wouldn't
> they need to tinker with overlong lines as  well?

Applications don't rely on /dev/vcsa. They use the ioctl(TIOCGWINSZ) on 
their output file descriptor.

BRLTTY could do that on /dev/tty and get the screen dimensions.

The problem is with the cursor position. By writing "\033[6n" to 
/dev/tty it is possible to read back a response string with the cursor 
position, but it is not clear to me how to prevent the actual program 
running on that terminal from consuming the response instead.

> Limiting BRLTTY users to screens with a larger font just because Linux 
> cannot deal with it doesn't seem appealing. I suppose the vcsa header 
> cannot be fixed due to backward compatibility concerns. What about the 
> vcsu headers, do they expose similar information,

No. vcsu is raw content like vcs (without the a).

The vcsua (orvcsau) is still not implemented as it is unclear what kind 
of attributes would be universally useful to export, and no one took the 
time to figure that out yet.

> would it be worth discussing with Linux devs changing it there?

Actually, that Linux dev would likely be me.  ;-)


Nicolas