emacs/doc/emacs/picture-xtra.texi

@c This is part of the Emacs manual.
@c Copyright (C) 2004-2017 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@c
@c This file is included either in emacs-xtra.texi (when producing the
@c printed version) or in the main Emacs manual (for the on-line version).
@node Picture Mode
@section Editing Pictures
@cindex pictures
@cindex making pictures out of text characters
@findex picture-mode

  To edit a picture made out of text characters (for example, a picture
of the division of a register into fields, as a comment in a program),
use the command @kbd{M-x picture-mode} to enter Picture mode.

  In Picture mode, editing is based on the @dfn{quarter-plane} model of
text, according to which the text characters lie studded on an area that
stretches infinitely far to the right and downward.  The concept of the end
of a line does not exist in this model; the most you can say is where the
last nonblank character on the line is found.

  Of course, Emacs really always considers text as a sequence of
characters, and lines really do have ends.  But Picture mode replaces
the most frequently-used commands with variants that simulate the
quarter-plane model of text.  They do this by inserting spaces or by
converting tabs to spaces.

  Most of the basic editing commands of Emacs are redefined by Picture mode
to do essentially the same thing but in a quarter-plane way.  In addition,
Picture mode defines various keys starting with the @kbd{C-c} prefix to
run special picture editing commands.

  One of these keys, @kbd{C-c C-c}, is particularly important.  Often
a picture is part of a larger file that is usually edited in some
other major mode.  Picture mode records the name of the previous major
mode so you can use the @kbd{C-c C-c} command
(@code{picture-mode-exit}) later to go back to that mode.  @kbd{C-c
C-c} also deletes spaces from the ends of lines, unless given a
numeric argument.

  The special commands of Picture mode all work in other modes (provided
the @file{picture} library is loaded), but are not bound to keys except
in Picture mode.  The descriptions below talk of moving ``one column''
and so on, but all the picture mode commands handle numeric arguments as
their normal equivalents do.

@vindex picture-mode-hook
  Turning on Picture mode runs the hook @code{picture-mode-hook}.
Additional extensions to Picture mode can be found in
@file{artist.el}.

@menu
* Basic Picture::         Basic concepts and simple commands of Picture Mode.
* Insert in Picture::     Controlling direction of cursor motion
                            after self-inserting characters.
* Tabs in Picture::       Various features for tab stops and indentation.
* Rectangles in Picture:: Clearing and superimposing rectangles.
@end menu

@node Basic Picture
@subsection Basic Editing in Picture Mode

@findex picture-forward-column
@findex picture-backward-column
@findex picture-move-down
@findex picture-move-up
@cindex editing in Picture mode

  Most keys do the same thing in Picture mode that they usually do, but
do it in a quarter-plane style.  For example, @kbd{C-f} is rebound to
run @code{picture-forward-column}, a command which moves point one
column to the right, inserting a space if necessary so that the actual
end of the line makes no difference.  @kbd{C-b} is rebound to run
@code{picture-backward-column}, which always moves point left one
column, converting a tab to multiple spaces if necessary.  @kbd{C-n} and
@kbd{C-p} are rebound to run @code{picture-move-down} and
@code{picture-move-up}, which can either insert spaces or convert tabs
as necessary to make sure that point stays in exactly the same column.
@kbd{C-e} runs @code{picture-end-of-line}, which moves to after the last
nonblank character on the line.  @kbd{C-a} runs
@code{picture-beginning-of-line}.  (The choice of screen model does not
affect beginnings of lines; the only extra thing this command does is
update the current picture column to 0.)

@findex picture-newline
  Insertion of text is adapted to the quarter-plane screen model
through the use of Overwrite mode
@iftex
(@pxref{Minor Modes,,, emacs, the Emacs Manual}.)
@end iftex
@ifnottex
(@pxref{Minor Modes}.)
@end ifnottex
Self-inserting characters replace existing text, column by column,
rather than pushing existing text to the right.  @key{RET} runs
@code{picture-newline}, which just moves to the beginning of the
following line so that new text will replace that line.

@findex picture-backward-clear-column
@findex picture-clear-column
@findex picture-clear-line
  In Picture mode, the commands that normally delete or kill text,
instead erase text (replacing it with spaces).  @key{DEL}
(@code{picture-backward-clear-column}) replaces the preceding
character with a space rather than removing it; this moves point
backwards.  @kbd{C-d} (@code{picture-clear-column}) replaces the next
character or characters with spaces, but does not move point.  (If you
want to clear characters to spaces and move forward over them, use
@key{SPC}.)  @kbd{C-k} (@code{picture-clear-line}) really kills the
contents of lines, but does not delete the newlines from the buffer.

@findex picture-open-line
  To do actual insertion, you must use special commands.  @kbd{C-o}
(@code{picture-open-line}) creates a blank line after the current
line; it never splits a line.  @kbd{C-M-o} (@code{split-line}) makes
sense in Picture mode, so it is not changed.  @kbd{C-j}
(@code{picture-duplicate-line}) inserts another line with the same
contents below the current line.

@kindex C-c C-d @r{(Picture mode)}
   To do actual deletion in Picture mode, use @kbd{C-w}, @kbd{C-c C-d}
(which is defined as @code{delete-char}, as @kbd{C-d} is in other
modes), or one of the picture rectangle commands (@pxref{Rectangles in
Picture}).

@node Insert in Picture
@subsection Controlling Motion after Insert

@findex picture-movement-up
@findex picture-movement-down
@findex picture-movement-left
@findex picture-movement-right
@findex picture-movement-nw
@findex picture-movement-ne
@findex picture-movement-sw
@findex picture-movement-se
@kindex C-c < @r{(Picture mode)}
@kindex C-c > @r{(Picture mode)}
@kindex C-c ^ @r{(Picture mode)}
@kindex C-c . @r{(Picture mode)}
@kindex C-c ` @r{(Picture mode)}
@kindex C-c ' @r{(Picture mode)}
@kindex C-c / @r{(Picture mode)}
@kindex C-c \ @r{(Picture mode)}
  Since self-inserting characters in Picture mode overwrite and move
point, there is no essential restriction on how point should be moved.
Normally point moves right, but you can specify any of the eight
orthogonal or diagonal directions for motion after a self-inserting
character.  This is useful for drawing lines in the buffer.

@table @kbd
@item C-c <
@itemx C-c @key{LEFT}
Move left after insertion (@code{picture-movement-left}).
@item C-c >
@itemx C-c @key{RIGHT}
Move right after insertion (@code{picture-movement-right}).
@item C-c ^
@itemx C-c @key{UP}
Move up after insertion (@code{picture-movement-up}).
@item C-c .
@itemx C-c @key{DOWN}
Move down after insertion (@code{picture-movement-down}).
@item C-c `
@itemx C-c @key{Home}
Move up and left (``northwest'') after insertion (@code{picture-movement-nw}).
@item C-c '
@itemx C-c @key{prior}
Move up and right (``northeast'') after insertion
(@code{picture-movement-ne}).
@item C-c /
@itemx C-c @key{End}
Move down and left (``southwest'') after insertion
@*(@code{picture-movement-sw}).
@item C-c \
@itemx C-c @key{next}
Move down and right (``southeast'') after insertion
@*(@code{picture-movement-se}).
@end table

@kindex C-c C-f @r{(Picture mode)}
@kindex C-c C-b @r{(Picture mode)}
@findex picture-motion
@findex picture-motion-reverse
  Two motion commands move based on the current Picture insertion
direction.  The command @kbd{C-c C-f} (@code{picture-motion}) moves in the
same direction as motion after insertion currently does, while @kbd{C-c
C-b} (@code{picture-motion-reverse}) moves in the opposite direction.

@node Tabs in Picture
@subsection Picture Mode Tabs

@kindex M-TAB @r{(Picture mode)}
@findex picture-tab-search
@vindex picture-tab-chars
  Two kinds of tab-like action are provided in Picture mode.  Use
@kbd{M-@key{TAB}} (@code{picture-tab-search}) for context-based tabbing.
With no argument, it moves to a point underneath the next
``interesting'' character that follows whitespace in the previous
nonblank line.  ``Next'' here means ``appearing at a horizontal position
greater than the one point starts out at''.  With an argument, as in
@kbd{C-u M-@key{TAB}}, this command moves to the next such interesting
character in the current line.  @kbd{M-@key{TAB}} does not change the
text; it only moves point.  ``Interesting'' characters are defined by
the variable @code{picture-tab-chars}, which should define a set of
characters.  The syntax for this variable is like the syntax used inside
of @samp{[@dots{}]} in a regular expression---but without the @samp{[}
and the @samp{]}.  Its default value is @code{"!-~"}.

@findex picture-tab
  @key{TAB} itself runs @code{picture-tab}, which operates based on the
current tab stop settings; it is the Picture mode equivalent of
@code{tab-to-tab-stop}.  Normally it just moves point, but with a numeric
argument it clears the text that it moves over.

@kindex C-c TAB @r{(Picture mode)}
@findex picture-set-tab-stops
  The context-based and tab-stop-based forms of tabbing are brought
together by the command @kbd{C-c @key{TAB}} (@code{picture-set-tab-stops}).
This command sets the tab stops to the positions which @kbd{M-@key{TAB}}
would consider significant in the current line.  The use of this command,
together with @key{TAB}, can get the effect of context-based tabbing.  But
@kbd{M-@key{TAB}} is more convenient in the cases where it is sufficient.

  It may be convenient to prevent use of actual tab characters in
pictures.  For example, this prevents @kbd{C-x @key{TAB}} from messing
up the picture.  You can do this by setting the variable
@code{indent-tabs-mode} to @code{nil}.

@node Rectangles in Picture
@subsection Picture Mode Rectangle Commands
@cindex rectangles and Picture mode
@cindex Picture mode and rectangles

  Picture mode defines commands for working on rectangular pieces of
the text in ways that fit with the quarter-plane model.  The standard
rectangle commands may also be useful.
@iftex
@xref{Rectangles,,, emacs, the Emacs Manual}.
@end iftex
@ifnottex
@xref{Rectangles}.
@end ifnottex

@table @kbd
@item C-c C-k
Clear out the region-rectangle with spaces
(@code{picture-clear-rectangle}).  With a prefix argument, delete the
text.
@item C-c C-w @var{r}
Similar, but save rectangle contents in register @var{r} first
(@code{picture-clear-rectangle-to-register}).
@item C-c C-y
Copy last killed rectangle into the buffer by overwriting, with upper
left corner at point (@code{picture-yank-rectangle}).  With argument,
insert instead.
@item C-c C-x @var{r}
Similar, but use the rectangle in register @var{r}
(@code{picture-yank-rectangle-from-register}).
@end table

@kindex C-c C-k @r{(Picture mode)}
@kindex C-c C-w @r{(Picture mode)}
@findex picture-clear-rectangle
@findex picture-clear-rectangle-to-register
  The picture rectangle commands @kbd{C-c C-k}
(@code{picture-clear-rectangle}) and @kbd{C-c C-w}
(@code{picture-clear-rectangle-to-register}) differ from the standard
rectangle commands in that they normally clear the rectangle instead of
deleting it; this is analogous with the way @kbd{C-d} is changed in Picture
mode.

  However, deletion of rectangles can be useful in Picture mode, so
these commands delete the rectangle if given a numeric argument.
@kbd{C-c C-k} either with or without a numeric argument saves the
rectangle for @kbd{C-c C-y}.

@kindex C-c C-y @r{(Picture mode)}
@kindex C-c C-x @r{(Picture mode)}
@findex picture-yank-rectangle
@findex picture-yank-rectangle-from-register
  The Picture mode commands for yanking rectangles differ from the
standard ones in that they overwrite instead of inserting.  This is
the same way that Picture mode insertion of other text differs from
other modes.  @kbd{C-c C-y} (@code{picture-yank-rectangle}) inserts
(by overwriting) the rectangle that was most recently killed, while
@kbd{C-c C-x} (@code{picture-yank-rectangle-from-register}) does
likewise for the rectangle found in a specified register.