Re: line-pixel-height beyond eol

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 13 Sep 2017 09:24:30 +0900 (JST)
> Cc: emacs-devel@gnu.org, tkk@misasa.okayama-u.ac.jp
> From: Tak Kunihiro <tkk@misasa.okayama-u.ac.jp>
> 
> > I don't think I understand what value you want to obtain.  Can you
> > elaborate, and perhaps also explain what do you want to do with that
> > value and why?
> 
> With Eww, I often meet pages with wide images.  I want to scroll
> pixel-wisely the buffers with auto-hscroll-mode off even when
> (current-column) is a large number.
> 
> The building block of pixel-wise scrolling is described as below.
> 
>   (progn (vertical-motion 1)
>          (dolist (vs (number-sequence 1 (1- (frame-char-height))))
>            (set-window-vscroll nil vs t) (sit-for 0.01))
>          (scroll-up 1))
> 
> To determine when to flush in a buffer of lines with different height,
> I have to know

Just a moment: why would you need to change the above code when lines
have variable height?  The above code scrolls the buffer one pixel at
a time until you scroll the height of frame's canonical character;
with tall lines, doing that will scroll less than the full line.  But
why is that a problem?  The user will just have to spin the wheel some
more.

>   - height of line in pixel of the top line on screen.

Why the top line on screen?  What is special about that line?

> I think that, on XXX condition, I rather should obtain it as
> frame-char-height instead of line-pixel-height.  I cannot find how to
> describe the XXX condition.

I think you may be trying a specific solution too early.  I'm not yet
sure I understand why the original code doesn't work for your needs.