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Go to the previous, next chapter.
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 M-x edit-picture to enter Picture mode.
In Picture mode, editing is based on the 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 C-c prefix to run special picture editing
commands.
One of these keys, C-c C-c, is pretty important. Often a picture is part of
a larger file that is usually edited in some other major mode. M-x edit-picture
records the name of the previous major mode so you can use the C-c C-c command (picture-mode-exit) later to go back
to that mode. 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 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.
Turning on Picture mode runs the hook picture-mode-hook (see section Hooks).
Most keys do the same thing in Picture mode that they usually do, but do it in a
quarter-plane style. For example, C-f is rebound to run 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. C-b is rebound to run picture-backward-column,
which always moves point left one column, converting a
tab to multiple spaces if necessary. C-n and C-p are rebound to run picture-move-down
and picture-move-up, which can either insert spaces or convert tabs as
necessary to make sure that point stays in exactly the
same column. C-e runs picture-end-of-line, which moves to after
the last nonblank character on the line. There is no
need to change C-a, as the choice of screen model does not affect beginnings of
lines.
Insertion of text
is adapted to the quarter-plane screen model through the use of Overwrite mode (see
section Minor Modes). Self-inserting characters replace
existing text, column by column, rather than pushing
existing text to the right. RET runs picture-newline, which just moves to the beginning of the
following line so that new text will replace that
line.
Picture mode provides erasure instead of deletion
and killing of text.
DEL (picture-backward-clear-column) replaces the preceding character with a space rather than removing it; this moves
point backwards. C-d (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 SPC.) C-k (picture-clear-line)
really kills the contents of lines, but does not delete the newlines from the buffer.
To do actual insertion, you must use special
commands. C-o (picture-open-line) creates a blank line after the
current line; it never splits a line. C-M-o, split-line, makes
sense in Picture mode, so it is not changed. LFD (picture-duplicate-line)
inserts below the current line another line with the same contents.
To do actual deletion in Picture mode, use C-w,
C-c C-d (which is defined as delete-char, as C-d is in
other modes), or one of the picture rectangle commands
(see section Picture Mode Rectangle Commands).
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.
- C-c Move left after insertion (
picture-movement-left).
C-c > Move right after insertion (picture-movement-right).
C-c ^ Move up after insertion (picture-movement-up).
C-c . Move down after insertion (picture-movement-down).
C-c ` Move up and left (``northwest'') after insertion
(picture-movement-nw). C-c ' Move up and right (``northeast'') after insertion (picture-movement-ne). C-c /
Move down and left (``southwest'') after insertion (picture-movement-sw).
C-c \ Move down and right (``southeast'') after insertion
(picture-movement-se).
Two motion commands move based on the current Picture insertion
direction. The command C-c C-f (picture-motion)
moves in the same direction as motion after ``insertion''
currently does, while C-c C-b (picture-motion-reverse) moves in
the opposite direction.
Two kinds of tab-like action are provided in Picture mode. Use M-TAB (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 C-u
M-TAB, this command moves to the next such
interesting character in the current line. M-TAB
does not change the text; it only moves point. ``Interesting'' characters are defined by the variable picture-tab-chars, which should
define a set of characters. The syntax for this variable
is like the syntax used inside of [...] in a regular expression---but without
the [ and the ]. Its default value is "!-~".
TAB itself runs picture-tab, which operates based on the
current tab stop settings; it is the Picture mode equivalent of tab-to-tab-stop.
Normally it just moves point, but with a numeric
argument it clears the text that it moves over.
The context-based and tab-stop-based forms of tabbing are brought together by the command C-c TAB, picture-set-tab-stops.
This command sets the tab stops to the positions which M-TAB
would consider significant in the current line. The use of this command, together with TAB, can get the effect
of context-based tabbing. But M-TAB is more convenient in the cases where it is
sufficient.
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 (see
section Rectangles).
- C-c C-k Clear out the region-rectangle with spaces (
picture-clear-rectangle). With argument, delete the text. C-c C-w r Similar but save rectangle contents in register r first (picture-clear-rectangle-to-register). C-c C-y Copy last
killed rectangle into the buffer by overwriting, with upper left corner at point (picture-yank-rectangle).
With argument, insert instead. C-c C-x r Similar, but use the rectangle in register r (picture-yank-rectangle-from-register).
The picture rectangle commands C-c C-k (picture-clear-rectangle) and C-c C-w (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 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. C-c C-k either with or without a numeric argument
saves the rectangle for C-c C-y.
The Picture mode commands for yanking rectangles
differ from the standard ones in overwriting instead of inserting. This is the same way
that Picture mode insertion of other text differs from other modes. C-c C-y (picture-yank-rectangle) inserts (by overwriting) the rectangle that was most recently killed, while C-c
C-x (picture-yank-rectangle-from-register)
does likewise for the rectangle found in a specified
register.
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