bug#1355: suggestion on the modeline

[Alan Mackenzie <acm@muc.de>]

Hi, R and X!

On Sun, Nov 16, 2008 at 09:57:21PM -0500, Richard M. Stallman wrote:

>       The cursor location percentage should by default not shown if  
>     emacs is running in GUI with scroll bar.

> Maybe so.

>       When emacs is running in a terminal, the special indicator  
>      Top  and  Bot  should be shown as percentage as usual,  

> "Top" is equivalent to 00%, and showing "00%" instead would
> be just as good.  However, "Bot" gives you other information:
> that the bottom of the buffer is on the screen.

Incidentally, I think the wrong percentage is displayed.  Assuming that
the window shows part of the buffer, there's stuff above, stuff below,
like this:

a               ^
a               |
a               |
a               |
  W             |              ^
  W             |              |
  W             |              |
  W          buffer         window
  W             |              |
  W             |              |
  W             |              v
b               |
b               |
b               |
b               v

, the percentage currently displayed is a / (a + W + b).  So, although in
the picture, the window is showing the middle of the buffer, the
percentage displayed is 22%, rather than 50%.  This is particularly
jarring when scrolling through, perhaps, an info page.  You see 47%, then
two lines later, Bot.

A better calculation would be a / (a + b), the degree of "travel" of the
windown through the buffer.  This approaches 100% as the window reaches
the bottom of the buffer.

I've been using this for many years now.  Here's how:

[ Emacs 22.3 ]
*** xdisp.orig.c	2008-08-26 15:45:44.000000000 +0000
--- xdisp.c	2008-09-12 13:59:17.000000000 +0000
***************
*** 18033,18041 ****
      case 'p':
        {
  	int pos = marker_position (w->start);
! 	int total = BUF_ZV (b) - BUF_BEGV (b);
  
! 	if (XFASTINT (w->window_end_pos) <= BUF_Z (b) - BUF_ZV (b))
  	  {
  	    if (pos <= BUF_BEGV (b))
  	      return "All";
--- 18033,18043 ----
      case 'p':
        {
  	int pos = marker_position (w->start);
!         int bottpos = BUF_Z (b) - XFASTINT (w->window_end_pos); /* ACM */
!         int totnotdisp = BUF_ZV (b) - BUF_BEGV (b) - (bottpos - pos); /* ACM */
! 	int total ;
  
!         if ((bottpos >= BUF_ZV (b)) || (totnotdisp <= 0)) /* ACM */
  	  {
  	    if (pos <= BUF_BEGV (b))
  	      return "All";
***************
*** 18046,18056 ****
  	  return "Top";
  	else
  	  {
! 	    if (total > 1000000)
  	      /* Do it differently for a large value, to avoid overflow.  */
! 	      total = ((pos - BUF_BEGV (b)) + (total / 100) - 1) / (total / 100);
  	    else
! 	      total = ((pos - BUF_BEGV (b)) * 100 + total - 1) / total;
  	    /* We can't normally display a 3-digit number,
  	       so get us a 2-digit number that is close.  */
  	    if (total == 100)
--- 18048,18060 ----
  	  return "Top";
  	else
  	  {
!             if (totnotdisp > 1000000)
  	      /* Do it differently for a large value, to avoid overflow.  */
! 	      total = ((pos - BUF_BEGV (b)) + (totnotdisp / 100) - 1)
!                       / (totnotdisp / 100); /* ACM */
  	    else
!               total = ((pos - BUF_BEGV (b)) * 100 + totnotdisp - 1)
!                       / totnotdisp ; /* ACM */
  	    /* We can't normally display a 3-digit number,
  	       so get us a 2-digit number that is close.  */
  	    if (total == 100)


-- 
Alan Mackenzie (Nuremberg, Germany).