Re: "... the window start at a meaningless point within a line."

[Alan Mackenzie <acm@muc.de>]

Hello, Eli.

On Mon, Oct 19, 2015 at 01:56:22PM +0300, Eli Zaretskii wrote:
> > Date: Mon, 19 Oct 2015 10:45:07 +0000
> > Cc: emacs-devel@gnu.org
> > From: Alan Mackenzie <acm@muc.de>

[ .... ]

> My problem is that you "flatten" the layout: where the actual layout
> is 2-dimensional, you make it 1-dimensional, and replace visual cues
> with those A2, L3 markers, that I can never remember which one is
> which.  Reasoning about VERTICAL motion while using a HORIZONTAL
> diagram doesn't help, either.

> So if you want to use diagrams, let's make them reflect the screen
> layout, like this:

>   B--------------------WS----------
>   A--------------------L1----------
>   A2------\n
>   C---------------------------\n
>   C2-------------------------\n

> etc., where a line without a \n at the end is continued on the next
> one.

> With this arrangement, the symbol's at the left can be discarded, and
> we only need the ones that are in the middle of the lines.

> If it's easier for you to have the lines start at WS and L1 instead of
> B and A, that's okay, too; we should just agree which convention we
> use.

I think I'd prefer to have the "actual" BOLs at the LHS.  But the
symbols at the left are still useful for discussion about a scenario.
For point, `it', and target, I suggest we write these below the line
they apply to, even though they look a little ambiguous there.  So, how
about this:

8. nlines = 3:
      B-------------------------------
WS----A-------------------------------
L1----A2------------------------------\n
   ^
C-------------------------------------
C2------------------------------------\n
it
C3------------------------------------
T

?

Here, point starts between L1 and A2, our target BOL is C3 (3 actual
BOLs after L1) and Fvertical_motion puts `it' at C2 (3 xdisp BOLs after
A).

-- 
Alan Mackenzie (Nuremberg, Germany).