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Re: flashing symptoms

From: Thomas Dickey
Subject: Re: flashing symptoms
Date: Thu, 9 Nov 2000 05:37:00 -0500

On Thu, Nov 09, 2000 at 07:28:09AM +0100, Frank Heckenbach wrote:
> Thomas E. Dickey wrote:
> > On Tue, 7 Nov 2000, Frank Heckenbach wrote:
> > 
> > > BTW, I recently wrote a program for a similar purpose. I called it
> > > tless (less with terminal control sequences sequences). It allows to
> > > step forward and back through a file with escape sequences. Stepping
> > > back is done be re-writing the complete file up to the new position,
> > > so it's not well suited for larger files. It's quite primitive, but
> > 
> > you probably could improve it by checking for clear-screen control
> > and verifying the cursor position at that point using the cursor position
> > report if it's properly implemented.
> Good idea. Just to make sure that I understand waht you mean:
> - scan the buffer for occurrences of clear_screen
> - after writing a clear_screen, get the current cursor position
>   (this means that clear_screen doesn't necessarily put the cursor
>   at the home position, right?) -- err, how do I get the cursor

right - that's why clear & home are often in the same initialization
string.  Many ANSI terminals support CPR (though I saw a recent comment
claiming it's broken in gnome-terminal ;-).  Getting the position after
clear-screen would always have the terminal in a known state that could
be easily reconstructed.

>   position? (I don't know so much about terminfo...)

There's some debug-code in ncurses that does that - would be simple to
make a function that does this.  tack uses u6 and u7 (user) strings for
this (see the comment in terminfo.src).  The code's in ncurses/tty/tty_update.c,
ifdef'd with POSITION_DEBUG (I happened to recall it since I recently fixed
a bug in it).
> - when scrolling back, restore (with cursor_address) the cursor
>   position after the last clear_screen, and write the buffer
>   starting after the clear_screen
> To facilitate multiple scrolling back, I would have to store each
> occurrence of clear_screen, not only the last one.

yes (but probably still faster than repainting all of the characters in

Thomas E. Dickey <address@hidden>

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