bug#16668: 24.3; Feature Request: Face to indicate lines displayed in window that are not part of the buffer.

bug#16668: 24.3; Feature Request: Face to indicate lines displayed in window that are not part of the buffer.

[Tim Visher]

I was told to submit a feature request via report-emacs-bug so I am.
Unfortunately, all the boilerplat around me seems to be related to bug
reports so I appologize in advance if I'm not following the correct
protocol.

I'd like some visual indication of where the contents of the buffer
ends. I've always thought it would be nice to have a different color
for the space beneath the buffer in the window.

So if I have a buffer with

```
this is the last line of text in the file


``` note the 2 blank lines at the bottom of the file

displayed in a window that looks like

```
snth
satoe
this is the last line of text in the file




``` Note the 2 extra blank lines

I'd like:

```
Normal Faces
Normal Faces
Normal Faces
Normal Faces
Normal Faces
Face indicating not part of buffer
Face indicating not part of buffer
```

Or something similar.


In GNU Emacs 24.3.1 (x86_64-apple-darwin13.0.0)
of 2013-10-27 on ts-macbook-air
Configured using:
`configure '--prefix=/usr/local/Cellar/emacs/24.3' '--without-dbus'
'--enable-locallisppath=/usr/local/share/emacs/site-lisp'
'--infodir=/usr/local/Cellar/emacs/24.3/share/info/emacs'
'--with-gnutls' '--without-x' 'CC=cc''

Important settings:
  value of $EMACSPATH: /Users/tim/.lein/bin:/Users/tim/bin:/usr/local/opt/coreutils/libexec/gnubin:/Users/tim/.gem/ruby/1.8/bin:/usr/local/bin:/usr/local/sbin:/Users/tim/bin:/usr/local/bin:/usr/local/sbin:/usr/bin:/bin:/usr/sbin:/sbin:/opt/X11/bin:/Users/tim/Dropbox/monetate/bin:/Users/tim/git/monetate-frontend/frontend/bin
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Org

Minor modes in effect:
  whitespace-mode: t
  winner-mode: t
  savehist-mode: t
  global-hl-line-mode: t
  cua-mode: t
  auto-insert-mode: t
  ido-vertical-mode: t
  flx-ido-mode: t
  ido-ubiquitous-mode: t
  show-paren-mode: t
  ido-everywhere: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
y y C-x C-f l u n c h a n d RET ESC > C-p C-e SPC - 
SPC H e a r d SPC o f SPC o n SPC C-h C-h C-h @ SPC 
[ [ h t t p : / / w w w . e v o l u t i o n n e w s 
. o r g / 2 0 1 4 / 0 2 / s i m o n _ p e y t o n _ 
j o 0 8 1 8 7 1 . h t m l ] [ S i m o n SPC P e y t 
o n SPC J o n e s SPC o n SPC " H o w SPC t o SPC W 
r i t e SPC a SPC G r e a t SPC R e s e a r c h SPC 
P a p e r " SPC - SPC E v o l u t i o n SPC N e w s 
SPC & SPC V i e w s ] ] C-a ESC f ESC f ESC f ESC f 
ESC f ESC f ESC f ESC f ESC f ESC f ESC f C-x C-s ESC 
x r e p o r t e RET

Recent messages:
you're loaded, Charnock!
Loading vc-git...done
Saving file /Users/tim/.emacs.d/timvisher/custom.el...
Wrote /Users/tim/.emacs.d/timvisher/custom.el [2 times]
Loading term/xterm...done
For information about GNU Emacs and the GNU system, type <f1> C-a.
OVERVIEW
Mark set
Saving file /Users/tim/Dropbox/lunchandlearn.org...
Wrote /Users/tim/Dropbox/lunchandlearn.org

Load-path shadows:
/Users/tim/.emacs.d/elpa/clojure-test-mode-3.0.0/clojure-test-mode hides ~/.emacs.d/site-lisp/clojure-test-mode
~/.emacs.d/timvisher/custom hides /usr/local/Cellar/emacs/24.3/share/emacs/24.3/lisp/custom

Features:
(shadow sort mail-extr emacsbug message rfc822 mml mml-sec mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils smex
org-wl org-w3m org-vm org-rmail org-mhe org-mew org-irc org-jsinfo
org-infojs org-html org-exp ob-exp org-exp-blocks org-agenda org-info
org-gnus gnus-util org-docview org-bibtex bibtex org-bbdb org byte-opt
warnings bytecomp byte-compile cconv ob-tangle ob-ref ob-lob ob-table
org-footnote org-src ob-comint ob-keys org-pcomplete pcomplete comint
ansi-color org-list org-faces org-entities noutline outline org-version
ob-emacs-lisp ob org-compat org-macs ob-eval org-loaddefs format-spec
find-func regexp-opt cal-menu calendar cal-loaddefs vc-git sensitive
sequences solarized-light-theme solarized-definitions cus-edit wid-edit
paredit eldoc elisp-slime-nav help-mode etags hideshow disp-table
whitespace winner ring savehist avoid hl-line cua-base autoinsert
cus-start cus-load server dired-x dired ido-vertical-mode flx-ido flx
ido-ubiquitous easy-mmode cl-macs gv cl ag-autoloads
align-cljlet-autoloads better-defaults-autoloads time-date paren edmacro
kmacro saveplace uniquify advice help-fns cl-lib advice-preload ido
clojure-test-mode-autoloads cider-autoloads clojure-mode-autoloads
dash-functional-autoloads deft-autoloads elein-autoloads
elisp-slime-nav-autoloads expand-region-autoloads
find-file-in-project-autoloads flx-ido-autoloads flx-autoloads
idle-highlight-mode-autoloads ido-ubiquitous-autoloads
ido-vertical-mode-autoloads magit-autoloads info tool-bar easymenu
markdown-mode-autoloads marmalade-autoloads furl-autoloads
paredit-autoloads pbcopy-autoloads projectile-autoloads
pkg-info-autoloads epl-autoloads s-autoloads sensitive-autoloads
sequences-autoloads smartparens-autoloads dash-autoloads finder-inf
smex-autoloads vimgolf-autoloads wgrep-autoloads yasnippet-autoloads
package ediff-hook vc-hooks lisp-float-type tabulated-list newcomment
lisp-mode register page menu-bar rfn-eshadow timer jit-lock font-lock
syntax facemenu font-core frame cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote make-network-process multi-tty emacs)

bug#16668: 24.3; Feature Request: Face to indicate lines displayed in window that are not part of the buffer.

[Eli Zaretskii]

> From: Tim Visher <tim.visher@gmail.com>
> Date: Thu, 6 Feb 2014 09:33:15 -0500
> 
> I'd like some visual indication of where the contents of the buffer
> ends. I've always thought it would be nice to have a different color
> for the space beneath the buffer in the window.
> 
> So if I have a buffer with
> 
> ```
> this is the last line of text in the file
> 
> 
> ``` note the 2 blank lines at the bottom of the file
> 
> displayed in a window that looks like
> 
> ```
> snth
> satoe
> this is the last line of text in the file
> 
> 
> 
> 
> ``` Note the 2 extra blank lines
> 
> I'd like:
> 
> ```
> Normal Faces
> Normal Faces
> Normal Faces
> Normal Faces
> Normal Faces
> Face indicating not part of buffer
> Face indicating not part of buffer
> ```
> 
> Or something similar.

A great introductory exercise for anyone who would like to gain
experience in hacking the Emacs display engine.  Volunteers are most
welcome.

bug#16668: 24.3; Feature Request: Face to indicate lines displayed in window that are not part of the buffer.

[Tim Visher]

On Thu, Feb 6, 2014 at 10:40 AM, Eli Zaretskii <eliz@gnu.org> wrote:
>> From: Tim Visher <tim.visher@gmail.com>
>> Date: Thu, 6 Feb 2014 09:33:15 -0500
>>
>> I'd like some visual indication of where the contents of the buffer
>> ends. I've always thought it would be nice to have a different color
>> for the space beneath the buffer in the window.
>>
>> So if I have a buffer with
>>
>> ```
>> this is the last line of text in the file
>>
>>
>> ``` note the 2 blank lines at the bottom of the file
>>
>> displayed in a window that looks like
>>
>> ```
>> snth
>> satoe
>> this is the last line of text in the file
>>
>>
>>
>>
>> ``` Note the 2 extra blank lines
>>
>> I'd like:
>>
>> ```
>> Normal Faces
>> Normal Faces
>> Normal Faces
>> Normal Faces
>> Normal Faces
>> Face indicating not part of buffer
>> Face indicating not part of buffer
>> ```
>>
>> Or something similar.
>
> A great introductory exercise for anyone who would like to gain
> experience in hacking the Emacs display engine.  Volunteers are most
> welcome.

Sounds intriguing. Could you perhaps point me to a couple places to
start? I wouldn't mind gaining said experience. :)

bug#16668: 24.3; Feature Request: Face to indicate lines displayed in window that are not part of the buffer.

[Eli Zaretskii]

> From: Tim Visher <tim.visher@gmail.com>
> Date: Mon, 10 Feb 2014 12:07:41 -0500
> Cc: 16668@debbugs.gnu.org
> 
> >> I'd like:
> >>
> >> ```
> >> Normal Faces
> >> Normal Faces
> >> Normal Faces
> >> Normal Faces
> >> Normal Faces
> >> Face indicating not part of buffer
> >> Face indicating not part of buffer
> >> ```
> >>
> >> Or something similar.
> >
> > A great introductory exercise for anyone who would like to gain
> > experience in hacking the Emacs display engine.  Volunteers are most
> > welcome.
> 
> Sounds intriguing. Could you perhaps point me to a couple places to
> start? I wouldn't mind gaining said experience. :)

Thanks for volunteering.

The place to start learning about the display engine is the large
commentary at the beginning of xdisp.c.

The next places to look areextend_face_to_end_of_line and
display_line, both defined in xdisp.c.

After that, ask specific questions (or go ahead and write code ;-).