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This library provides improved vertical scrolling commands for GNU Emacs.
47.1 Features | ||
47.2 Command and Functions | ||
47.3 Installation | ||
47.4 Advanced Customization |
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The new vertical scrolling commands offer the following features:
The variable scroll-in-place
, which is true by default, determines
whether or not the standard GNU Emacs scrolling commands (scroll-down
,
scroll-up
, scroll-other-window-down
, and
scroll-other-window
) use the "in place" features listed here. When
scroll-in-place
is nil the standard GNU Emacs scrolling commands
essentially just call the original versions of themselves. (Note that even
when scroll-in-place
is nil the new versions of scroll-down
and
scroll-up
have slightly different behavior when a minibuffer window is
the selected window. See below.)
It is possible to turn off (or turn on) "in place" scrolling for certain
buffers by making buffer-local bindings of the variable
scroll-in-place
for those buffers. The variable
scroll-in-place
is not usually buffer-local, but you can make it so if
you desire.
scroll-up
command undoes the effect of the immediately previous scroll-down
command (if any) and vice versa. In other words, if you scroll up and then
immediately scroll back down, the window configuration is restored to its
exact original state. This allows you to browse through a buffer more
easily, as you can always get back to the original configuration.
Note, however, that the improved scrolling commands are guaranteed to be reversible only if there are no intervening non-scrolling commands. Also, if you give a prefix argument to a scrolling command (in order to specify the number of lines to scroll by), previous scrolling commands may no longer be reversible. More specifically, if the new prefix argument has a different magnitude than the previous scrolling distance, then any previous scrolling commands are not reversible. The new prefix argument takes precedence.
You might find it useful to think of the scrolling commands as forming "chains." A scrolling command either starts or continues a chain. By issuing a non-scrolling command or by changing the number of lines to be scrolled, you break the chain. (Note that simply changing the scrolling direction won’t break the chain; changing the absolute number of lines to be scrolled is what breaks the chain.) Scrolling commands are guaranteed to be reversible only within the current chain. Hopefully that’s clear enough.
However, there are cases in which one doesn’t want the current scrolling
command to use the default scrolling distance that was set by the previous
scrolling command. For example, suppose that you had special commands that
scrolled one line up and one line down. When you invoke one of these
commands, the "in place" scrolling routines set the default scrolling
distance to be just one line. Now suppose that you use one of your special
commands and then immediately invoke scroll-up
(C-v), expecting
it to scroll by a near windowful of text. You would be disappointed —
because the previous command set the default scrolling distance to be just
one line, scroll-up
just scrolls by one line.
To solve this problem, "scroll-in-place" allows you to divide scrolling commands into separate "groups." Commands in a group can only form chains with (and therefore, inherit defaults from) commands in the same group. (Note that no command can be in more than one group.) If you invoke a scrolling command that is not in the same group as that of the immediately previous scrolling command, then the previous chain is broken and you start a new chain — with a new set of defaults.
So to solve the problem described above, you could put your one-line scrolling commands in their own group. Once that is done, the standard scrolling commands will not form chains with your one-line scrolling commands, and therefore will not use the default scrolling distance set by those commands. Problem solved!
By default, all "in place" scrolling commands are in a single group. If you
want to partition some commands into separate groups, you must do that
yourself before any "in place" commands are invoked. For more
information about grouping commands, see the documentation for the variables
scroll-command-groups
and scroll-default-command-group
.
scroll-allow-blank-lines-past-eob
.
Dead space will be displayed if it is necessary in order to make a previous scrolling action reversible, however.
However, if point was already at the buffer boundary when the scrolling command was invoked, the command signals an appropriate error instead.
scroll-up
and scroll-down
either scroll the window in the
variable minibuffer-scroll-window
(which is usually the window of
completions) or the next-window
if there is no
minibuffer-scroll-window
. This is usually much more useful than
scrolling the minibuffer itself. (Note that this feature is available even
when the variable scroll-in-place
is nil.)
(If an error were not signalled in these cases, then there would be many cases in which the last scroll in a particular direction would appear to do nothing because only the point position would change — the displayed text would stay the same! To avoid these cases the scrolling commands signal boundary errors "prematurely" when the window to be scrolled is not selected.)
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This library provides the following "in place" versions of GNU Emacs’ standard vertical scrolling commands:
The variable scroll-in-place
, which is true by default, determines
whether or not the new versions of the standard GNU Emacs scrolling commands
(scroll-down
, scroll-up
, scroll-other-window-down
, and
scroll-other-window
) use the "in place" features listed above. When
scroll-in-place
is nil the standard GNU Emacs scrolling commands
essentially just call the original versions of themselves. (Note that even
when scroll-in-place
is nil the new versions of scroll-down
and
scroll-up
have slightly different behavior when a minibuffer window is
the selected window. See the feature list above.)
NOTE that this package redefines the standard GNU Emacs commands
scroll-down
, scroll-up
, scroll-other-window-down
, and
scroll-other-window
(in order to check the variable
scroll-in-place
, as described above). The command
scroll-other-window-down
first appeared as a standard command in the
FSF’s GNU Emacs 19.26.
This package also provides the following functions and variables which are of use to programmers:
The scroll-window-in-place
function is the heart of the "in place"
scrolling commands. scroll-window
is a function that checks the
variable scroll-in-place
and calls the appropriate scrolling function
(either scroll-window-in-place
or one of the original versions of
scroll-down
and scroll-up
). The function
scroll-window-in-place-continue-sequence
is provided in order to
preserve running "chains" of scrolling commands as described above.
The variable scroll-default-lines
determines the default scrolling
distance when a new chain of "in place" scrolling commands begins. If this
variable is not a number, then the default distance is the height of the
window to be scrolled minus next-screen-context-lines
. The variable
scroll-command-groups
contains the explicit groups of "in place"
scrolling commands; for more information read the variable documentation.
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To use this package, you simply need to load it from within your initialization file:
(require 'scroll-in-place) |
By default, this package provides for the standard GNU Emacs vertical
scrolling commands (scroll-down
, scroll-up
,
scroll-other-window-down
, and scroll-other-window
) to use the
"in place" features. If you would rather not have this, set the variable
(setq scroll-in-place nil)
.
When scroll-in-place
is nil you will have to bind keys in order to
call the "in place" scrolling commands. For example, you might want to do
the following:
(global-set-key "\M-v" 'scroll-down-in-place) (global-set-key "\C-v" 'scroll-up-in-place) |
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If you want to partition certain "in place" scrolling commands into separate groups, you should do something like the following:
;; Make one group containing the commands `scroll-down-one-line' and ;; `scroll-up-one-line'. (These are not standard GNU Emacs commands.) (setq scroll-command-groups (list '(scroll-down-one-line scroll-up-one-line))) |
You could write the ‘scroll-down-one-line’ command like this:
(defun scroll-down-one-line (arg) "Scroll down one line, or number of lines specified by prefix arg." (interactive "P") (let ((scroll-default-lines 1)) (scroll-down-in-place arg))) |
If you want to disable "in place" scrolling for windows that display a
particular buffer (while leaving it available in other windows), you can make
scroll-in-place
a buffer-local variable for that buffer and then bind
that local copy of scroll-in-place
to nil. This is the kind of thing
that one generally does in a major mode hook. For example, you can disable
"in place" scrolling of GNUS article windows with the following code:
(setq gnus-article-mode-hook (function (lambda () (make-local-variable 'scroll-in-place) (setq scroll-in-place nil)))) ;; Set the variable `gnus-Article-mode-hook' instead if you are using ;; an old version of GNUS, say version 3.13 or 3.14. |
The variable scroll-allow-blank-lines-past-eob
can also be made local
to particular buffers, if you desire. (But why would you want to do that?)
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