bug#21012: 25.0.50; eww: last char of a line sometimes not fully visible

[Michael Heerdegen <michael_heerdegen@web.de>]

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Hello!

in eww, using shr-use-fonts -> t, for some lines, the last character is
only partially visible.  Not a big deal, but distracting.

Here is a screenshot made with emacs -Q:


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The issue seems to happen more likely with larger fonts (e.g. with
text-scale-mode -- of course I had hitten g after rescaling), but it
also happens with the default font here.

While browsing through and playing with the code, I found two places
where I could improve things:

1.

--8<---------------cut here---------------start------------->8---
(defun shr-insert-document (dom)
  ...
  (setq shr-content-cache nil)
  (let ((start (point))
	(shr-start nil)
        ...
	(shr-internal-width (or (and shr-width..3..)
				(if (not shr-use-fonts)
				    (- (window-width) 2)
				  (- (window-pixel-width) ; <---- here
				     (* (frame-fringe-width) 2))))))
    (shr-descend dom)
    (shr-fill-lines start (point))
    (shr-remove-trailing-whitespace start (point))
    (when shr-warning..1..)))
--8<---------------cut here---------------end--------------->8---

AFAICT

  (- (window-pixel-width) (* (frame-fringe-width) 2))

is not the available width for text, it is a larger value including
scroll bars etc.  When I change it to

  (window-body-width nil t)

this improves things.  The issue still occurs with this change, though
much less often.


2.

--8<---------------cut here---------------start------------->8---
(defun shr-vertical-motion (column)
  (if (not shr-use-fonts)
      (move-to-column column)
    (unless (eolp)
      (forward-char 1))
    (vertical-motion (cons (/ column (frame-char-width)) 0)) ; <-- here
    (unless (eolp)
      (forward-char 1))))
--8<---------------cut here---------------end--------------->8---

This function is used, among other places, to decide where to break
lines in `shr-fill-line'.

Probably (/ column (frame-char-width)) can be too large if you are
unlucky.  For testing I tried with this version:

--8<---------------cut here---------------start------------->8---
(defun shr-vertical-motion (column)
  (if (not shr-use-fonts)
      (move-to-column column)
    (unless (eolp)
      (forward-char 1))
    (end-of-visual-line)))
--8<---------------cut here---------------end--------------->8---

This seems to fix this issue (together with the first change), though I
guess it's wrong when shr-vertical-motion is called with column <
window-width (dunno if this is done somewhere).


Thanks,

Michael.




In GNU Emacs 25.0.50.4 (x86_64-unknown-linux-gnu, GTK+ Version 3.16.4)
 of 2015-07-07 on drachen
Repository revision: 0bfc94047da4960af55196242728a7a55120867f
Windowing system distributor `The X.Org Foundation', version 11.0.11702000
System Description:	Debian GNU/Linux testing (stretch)

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GSETTINGS NOTIFY
LIBXML2 FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11