emacs/lisp/textmodes/picture.el

;;; picture.el --- "Picture mode" -- editing using quarter-plane screen model -*- lexical-binding: t -*-

;; Copyright (C) 1985-2023 Free Software Foundation, Inc.

;; Author: K. Shane Hartman
;; Maintainer: emacs-devel@gnu.org
;; Keywords: convenience wp

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; This code provides the `picture-mode' commands documented in the Emacs
;; manual.  The screen is treated as a semi-infinite quarter-plane with
;; support for rectangle operations and "etch-a-sketch" character
;; insertion in any of eight directions.

;;; Code:

(defgroup picture nil
  "Editing text-based pictures (\"ASCII art\")."
  :prefix "picture-"
  :group 'text)

(defcustom picture-rectangle-ctl ?+
  "Character `picture-draw-rectangle' uses for top left corners."
  :type 'character)
(defcustom picture-rectangle-ctr ?+
  "Character `picture-draw-rectangle' uses for top right corners."
  :type 'character)
(defcustom picture-rectangle-cbr ?+
  "Character `picture-draw-rectangle' uses for bottom right corners."
  :type 'character)
(defcustom picture-rectangle-cbl ?+
  "Character `picture-draw-rectangle' uses for bottom left corners."
  :type 'character)
(defcustom picture-rectangle-v   ?|
  "Character `picture-draw-rectangle' uses for vertical lines."
  :type 'character)
(defcustom picture-rectangle-h   ?-
  "Character `picture-draw-rectangle' uses for horizontal lines."
  :type 'character)


;; Picture Movement Commands

(defvar picture-desired-column 0
  "Desired current column for Picture mode.
When a cursor is on a wide-column character (e.g. Chinese,
Japanese, Korean), this may be different from `current-column'.")


(defun picture-update-desired-column (adjust-to-current)
  "Maybe update `picture-desired-column'.
If the value of `picture-desired-column' is more than one column
from `current-column', or if the argument ADJUST-TO-CURRENT is
non-nil, set it to the current column.  Return `current-column'."
  (let ((current-column (current-column)))
    (if (or adjust-to-current
	    (< picture-desired-column (1- current-column))
	    (> picture-desired-column (1+ current-column)))
	(setq picture-desired-column current-column))
    current-column))

(defun picture-beginning-of-line (&optional arg)
  "Position point at the beginning of the line.
With ARG not nil, move forward ARG - 1 lines first.
If scan reaches end of buffer, stop there without error."
  (interactive "^P")
  (if arg (forward-line (1- (prefix-numeric-value arg))))
  (beginning-of-line)
  (setq picture-desired-column 0))

(defun picture-end-of-line (&optional arg)
  "Position point after last non-blank character on current line.
With ARG not nil, move forward ARG - 1 lines first.
If scan reaches end of buffer, stop there without error."
  (interactive "^P")
  (if arg (forward-line (1- (prefix-numeric-value arg))))
  (beginning-of-line)
  (skip-chars-backward " \t" (prog1 (point) (end-of-line)))
  (setq picture-desired-column (current-column)))

(defun picture-forward-column (arg &optional interactive)
  "Move cursor right, making whitespace if necessary.
With prefix argument ARG, move that many columns."
  (interactive "^p\nd")
  (let (deactivate-mark)
    (picture-update-desired-column interactive)
    (setq picture-desired-column (max 0 (+ picture-desired-column arg)))
    (let ((current-column (move-to-column picture-desired-column t)))
      (if (and (> current-column picture-desired-column)
	       (< arg 0))
	  ;; It seems that we have just tried to move to the right
	  ;; column of a multi-column character.
	  (forward-char -1)))))

(defun picture-backward-column (arg &optional interactive)
  "Move cursor left, making whitespace if necessary.
With prefix argument ARG, move that many columns."
  (interactive "^p\nd")
  (picture-update-desired-column interactive)
  (picture-forward-column (- arg)))

(defun picture-move-down (arg)
  "Move vertically down, making whitespace if necessary.
With prefix argument ARG, move that many lines."
  (interactive "^p")
  (let (deactivate-mark)
    (picture-update-desired-column nil)
    (picture-newline arg)
    (let ((current-column (move-to-column picture-desired-column t)))
      (if (> current-column picture-desired-column)
	  (forward-char -1)))))

(defvar picture-vertical-step 0
  "Amount to move vertically after text character in Picture mode.")

(defvar picture-horizontal-step 1
  "Amount to move horizontally after text character in Picture mode.")

(defun picture-move-up (arg)
  "Move vertically up, making whitespace if necessary.
With prefix argument ARG, move that many lines."
  (interactive "^p")
  (picture-update-desired-column nil)
  (picture-move-down (- arg)))

(defun picture-movement-right ()
  "Move right after self-inserting character in Picture mode."
  (interactive)
  (picture-set-motion 0 1))

(defun picture-movement-left ()
  "Move left after self-inserting character in Picture mode."
  (interactive)
  (picture-set-motion 0 -1))

(defun picture-movement-up ()
  "Move up after self-inserting character in Picture mode."
  (interactive)
  (picture-set-motion -1 0))

(defun picture-movement-down ()
  "Move down after self-inserting character in Picture mode."
  (interactive)
  (picture-set-motion 1 0))

(defun picture-movement-nw (&optional arg)
  "Move up and left after self-inserting character in Picture mode.
With prefix argument ARG, move up and two-column left."
  (interactive "P")
  (picture-set-motion -1 (if arg -2 -1)))

(defun picture-movement-ne (&optional arg)
  "Move up and right after self-inserting character in Picture mode.
With prefix argument ARG, move up and two-column right."
  (interactive "P")
  (picture-set-motion -1 (if arg 2 1)))

(defun picture-movement-sw (&optional arg)
  "Move down and left after self-inserting character in Picture mode.
With prefix argument ARG, move down and two-column left."
  (interactive "P")
  (picture-set-motion 1 (if arg -2 -1)))

(defun picture-movement-se (&optional arg)
  "Move down and right after self-inserting character in Picture mode.
With prefix argument ARG, move down and two-column right."
  (interactive "P")
  (picture-set-motion 1 (if arg 2 1)))

(defun picture-set-motion (vertical horizontal)
  "Set VERTICAL and HORIZONTAL increments for movement in Picture mode.
The mode line is updated to reflect the current direction."
  (setq picture-vertical-step vertical
        picture-horizontal-step horizontal)
  (setq mode-name
	(format "Picture:%s"
                (nth (+ 2 (% horizontal 3) (* 5 (1+ (% vertical 2))))
		     '(wnw nw up ne ene Left left none right Right
			   wsw sw down se ese))))
  (force-mode-line-update)
  (message ""))

(defun picture-move ()
  "Move in direction of `picture-vertical-step' and `picture-horizontal-step'."
  (if (/= picture-vertical-step 0)
      (picture-move-down picture-vertical-step))
  (if (/= picture-horizontal-step 0)
      (picture-forward-column picture-horizontal-step)))

(defun picture-motion (arg)
  "Move point in direction of current picture motion in Picture mode.
With ARG do it that many times.  Useful for delineating rectangles in
conjunction with diagonal picture motion.
Use \"\\[command-apropos] picture-movement\" to see commands which control motion."
  (interactive "^p")
  (picture-move-down (* arg picture-vertical-step))
  (picture-forward-column (* arg picture-horizontal-step)))

(defun picture-motion-reverse (arg)
  "Move point in direction opposite of current picture motion in Picture mode.
With ARG do it that many times.  Useful for delineating rectangles in
conjunction with diagonal picture motion.
Use \"\\[command-apropos] picture-movement\" to see commands which control motion."
  (interactive "^p")
  (picture-motion (- arg)))

(defun picture-mouse-set-point (event)
  "Move point to the position of EVENT, making whitespace if necessary."
  (interactive "e")
  (let ((position (event-start event)))
    (unless (posn-area position) ; Ignore EVENT unless in text area
      (let* ((window (posn-window position))
	     (frame  (if (framep window) window (window-frame window)))
	     (pair   (posn-x-y position))
	     (start-pos (window-start window))
	     (start-pair (posn-x-y (posn-at-point start-pos)))
	     (dx (- (car pair) (car start-pair)))
	     (dy (- (cdr pair) (cdr start-pair)))
	     (char-ht (frame-char-height frame))
	     (spacing (when (display-graphic-p frame)
			(or (with-current-buffer (window-buffer window)
			      line-spacing)
			    (frame-parameter frame 'line-spacing)))))
	(cond ((floatp spacing)
	       (setq spacing (truncate (* spacing char-ht))))
	      ((null spacing)
	       (setq spacing 0)))
	(goto-char start-pos)
	(picture-move-down      (/ dy (+ char-ht spacing)))
	(picture-forward-column (/ dx (frame-char-width frame)))))))


;; Picture insertion and deletion.

(defun picture-insert (ch arg)
  (let* ((width (char-width ch))
	 ;; We must be sure that the succeeding insertion won't delete
	 ;; the just inserted character.
	 (picture-horizontal-step
	  (if (and (= picture-vertical-step 0)
		   (> width 1)
		   (< (abs picture-horizontal-step) 2))
	      (* picture-horizontal-step 2)
	    picture-horizontal-step)))
    (while (> arg 0)
      (setq arg (1- arg))
      (if (/= picture-desired-column (current-column))
	  (move-to-column picture-desired-column t))
      (let ((col (+ picture-desired-column width)))
	(or (eolp)
	    (let ((pos (point)))
	      (move-to-column col t)
	      (let ((old-width (string-width (buffer-substring pos (point)))))
		(delete-region pos (point))
		(when (> old-width width)
		  (insert-char ?  (- old-width width))
		  (goto-char pos))))))
      (insert ch)
      (forward-char -1)
      (picture-move))))

(defun picture-self-insert (arg)
  "Insert this character in place of character previously at the cursor.
The cursor then moves in the direction you previously specified
with the commands `picture-movement-right', `picture-movement-up', etc.
Use \"\\[command-apropos] picture-movement\" to see those commands."
  (interactive "p")
  (picture-update-desired-column (not (eq this-command last-command)))
  (picture-insert last-command-event arg)) ; Always a character in this case.

(defun picture-clear-column (arg)
  "Clear out ARG columns after point without moving."
  (interactive "p")
  (let* ((original-col (current-column))
	 (target-col (max 0 (+ original-col arg)))
	 pos)
    (move-to-column target-col t)
    (setq pos (point))
    (move-to-column original-col)
    (delete-region pos (point))
    (save-excursion
     (indent-to (max target-col original-col))))
  (setq picture-desired-column (current-column)))

(defun picture-backward-clear-column (arg)
  "Clear out ARG columns before point, moving back over them."
  (interactive "p")
  (picture-clear-column (- arg)))

(defun picture-clear-line (arg)
  "Clear out rest of line; if at end of line, advance to next line.
Cleared-out line text goes into the kill ring, as do newlines
that are advanced over.  With prefix argument ARG, clear out (and
save in kill ring) that many lines."
  (interactive "P")
  (if arg
      (progn
       (setq arg (prefix-numeric-value arg))
       (kill-line arg)
       (newline (if (> arg 0) arg (- arg))))
    (if (looking-at "[ \t]*$")
	(kill-ring-save (point) (progn (forward-line 1) (point)))
      (kill-region (point) (progn (end-of-line) (point))))))

(defun picture-newline (arg)
  "Move to the beginning of the following line.
With prefix argument ARG, move that many lines (up, if negative
argument);
always moves to the beginning of a line."
  (interactive "^p")
  (let ((start (point))
        (lines-left (forward-line arg)))
    (if (and (eobp)
             (> (point) start))
        (newline))
    (if (> lines-left 0)
        (newline lines-left))))

(defun picture-open-line (arg)
  "Insert ARG empty lines after the current line.
ARG must be positive.
Interactively, ARG is the numeric argument, and defaults to 1."
  (interactive "p")
  (save-excursion
   (end-of-line)
   (open-line arg)))

(defun picture-duplicate-line ()
  "Insert a duplicate of the current line, below it."
  (interactive)
  (save-excursion
   (let ((contents
	  (buffer-substring
	   (progn (beginning-of-line) (point))
	   (progn (picture-newline 1) (point)))))
     (forward-line -1)
     (insert contents))))

;; Like replace-match, but overwrites.
(defun picture-replace-match (newtext fixedcase literal)
  (let (ocolumn change pos)
    (goto-char (setq pos (match-end 0)))
    (setq ocolumn (current-column))
    ;; Make the replacement and undo it, to see how it changes the length.
    (let ((buffer-undo-list nil)
	  list1)
      (replace-match newtext fixedcase literal)
      (setq change (- (current-column) ocolumn))
      (setq list1 buffer-undo-list)
      (while list1
	(setq list1 (primitive-undo 1 list1))))
    (goto-char pos)
    (if (> change 0)
	(delete-region (point)
		       (progn
			 (move-to-column (+ change (current-column)) t)
			 (point))))
    (replace-match newtext fixedcase literal)
    (if (< change 0)
	(insert-char ?\s (- change)))))

;; Picture Tabs

(defcustom picture-tab-chars "!-~"
  "A character set which controls behavior of commands.
\\[picture-set-tab-stops] and \\[picture-tab-search].
The syntax for this variable is like the syntax used inside of `[...]'
in a regular expression--but without the `[' and the `]'.
It is NOT a regular expression, and should follow the usual
rules for the contents of a character alternative.
It defines a set of \"interesting characters\" to look for when setting
\(or searching for) tab stops, initially \"!-~\" (all printing characters).
For example, suppose that you are editing a table which is formatted thus:
| foo		| bar + baz | 23  *
| bubbles	| and + etc | 97  *
and that `picture-tab-chars' is \"|+*\".  Then invoking
\\[picture-set-tab-stops] on either of the previous lines would result
in the following tab stops
		:     :     :     :
Another example - \"A-Za-z0-9\" would produce the tab stops
  :		  :	:     :

Note that if you want the character `-' to be in the set, it must be
included in a range or else appear in a context where it cannot be
taken for indicating a range (e.g. \"-A-Z\" declares the set to be the
letters `A' through `Z' and the character `-').  If you want the
character `\\' in the set it must be preceded by itself: \"\\\\\".

The command \\[picture-tab-search] is defined to move beneath (or to) a
character belonging to this set independent of the tab stops list."
  :type 'string)

(defun picture-set-tab-stops (&optional arg)
  "Set value of `tab-stop-list' according to context of this line.
This controls the behavior of \\[picture-tab].  A tab stop is set at
every column occupied by an \"interesting character\" that is preceded
by whitespace.  Interesting characters are defined by the variable
`picture-tab-chars', see its documentation for an example of usage.
With ARG, just (re)set `tab-stop-list' to its default value.  The tab
stops computed are displayed in the minibuffer with `:' at each stop."
  (interactive "P")
  (save-excursion
    (let (tabs)
      (if arg
	  (setq tabs (or (default-value 'tab-stop-list)
			 (indent-accumulate-tab-stops (window-width))))
	(let ((regexp (concat "[ \t]+[" picture-tab-chars "]")))
	  (beginning-of-line)
	  (let ((bol (point)))
	    (end-of-line)
	    (while (re-search-backward regexp bol t)
	      (skip-chars-forward " \t")
	      (setq tabs (cons (current-column) tabs)))
	    (if (null tabs)
		(error "No characters in set [%s] on this line"
		       picture-tab-chars)))))
      (setq tab-stop-list tabs)
      (let ((blurb (make-string (1+ (nth (1- (length tabs)) tabs)) ?\ )))
	(while tabs
	  (aset blurb (car tabs) ?:)
	  (setq tabs (cdr tabs)))
	(message blurb)))))

(defun picture-tab-search (&optional arg)
  "Move to column beneath next interesting char in previous line.
With ARG move to column occupied by next interesting character in this
line.  The character must be preceded by whitespace.
\"interesting characters\" are defined by variable `picture-tab-chars'.
If no such character is found, move to beginning of line."
  (interactive "^P")
  (let ((target (current-column)))
    (save-excursion
      (if (and (not arg)
	       (progn
		 (beginning-of-line)
		 (skip-chars-backward
		  (concat "^" (string-replace
			       "\\" "\\\\" picture-tab-chars))
		  (point-min))
		 (not (bobp))))
	  (move-to-column target))
      (if (re-search-forward
	   (concat "[ \t]+[" picture-tab-chars "]")
	   (line-end-position)
	   'move)
	  (setq target (1- (current-column)))
	(setq target nil)))
    (if target
	(move-to-column target t)
      (beginning-of-line))))

(defun picture-tab (&optional arg)
  "Tab transparently (just move point) to next tab stop.
With prefix argument ARG, overwrite the traversed text with
spaces.  The tab stop list can be changed by \
\\<picture-mode-map>\\[picture-set-tab-stops] and
\\[edit-tab-stops].

See also documentation for variable `picture-tab-chars'."
  (interactive "^P")
  (let* ((opoint (point)))
    (move-to-tab-stop)
    (if arg
	(let (indent-tabs-mode
	      (column (current-column)))
	  (delete-region opoint (point))
	  (indent-to column)))))

;; Picture Rectangles

(defvar picture-killed-rectangle nil
  "Rectangle killed or copied by \\[picture-clear-rectangle] in Picture mode.
The contents can be retrieved by \\[picture-yank-rectangle]")

(defun picture-clear-rectangle (start end &optional killp)
  "Clear and save rectangle delineated by point and mark.
The rectangle is saved for yanking by \\[picture-yank-rectangle] and replaced
with whitespace.  The previously saved rectangle, if any, is lost.  With
prefix argument, the rectangle is actually killed, shifting remaining text."
  (interactive "r\nP")
  (setq picture-killed-rectangle (picture-snarf-rectangle start end killp)))

(defun picture-clear-rectangle-to-register (start end register &optional killp)
  "Clear rectangle delineated by point and mark into REGISTER.
The rectangle is saved in REGISTER and replaced with whitespace.  With
prefix argument, the rectangle is actually killed, shifting remaining text.

Interactively, reads the register using `register-read-with-preview'."
  (interactive (list (region-beginning) (region-end)
		     (register-read-with-preview "Rectangle to register: ")
		     current-prefix-arg))
  (set-register register (picture-snarf-rectangle start end killp)))

(defun picture-snarf-rectangle (start end &optional killp)
  (let ((column (current-column))
	(indent-tabs-mode nil))
    (prog1 (save-excursion
             (if killp
                 (delete-extract-rectangle start end)
               (prog1 (extract-rectangle start end)
                      (clear-rectangle start end))))
	   (move-to-column column t))))

(defun picture-yank-rectangle (&optional insertp)
  "Overlay rectangle saved by \\[picture-clear-rectangle].
The rectangle is positioned with upper left corner at point,
overwriting existing text.  With prefix argument INSERTP, the
rectangle is inserted instead, shifting existing text.  Leave
mark at one corner of rectangle and point at the
other (diagonally opposed) corner."
  (interactive "P")
  (if (not (consp picture-killed-rectangle))
      (error "No rectangle saved")
    (picture-insert-rectangle picture-killed-rectangle insertp)))

(defun picture-yank-at-click (click arg)
  "Insert the last killed rectangle at the position clicked on.
Also move point to one end of the text thus inserted (normally the end).
Prefix arguments are interpreted as with \\[yank].
If `mouse-yank-at-point' is non-nil, insert at point
regardless of where you click."
  (interactive "e\nP")
  (or mouse-yank-at-point (mouse-set-point click))
  (picture-yank-rectangle arg))

(defun picture-yank-rectangle-from-register (register &optional insertp)
  "Overlay rectangle saved in REGISTER.
The rectangle is positioned with upper left corner at point,
overwriting existing text.  With prefix argument INSERTP, the
rectangle is inserted instead, shifting existing text.  Leave
mark at one corner of rectangle and point at the
other (diagonally opposed) corner.

Interactively, reads the register using `register-read-with-preview'."
  (interactive (list (register-read-with-preview "Rectangle from register: ")
		     current-prefix-arg))
  (let ((rectangle (get-register register)))
    (if (not (consp rectangle))
	(error "Register %c does not contain a rectangle" register)
      (picture-insert-rectangle rectangle insertp))))

(defun picture-insert-rectangle (rectangle &optional insertp)
  "Overlay RECTANGLE with upper left corner at point.
Optional argument INSERTP, if non-nil causes RECTANGLE to be inserted.
Leave the region surrounding the rectangle."
  (let ((indent-tabs-mode nil))
    (if (not insertp)
	(save-excursion
	  (delete-rectangle (point)
			    (progn
			      (picture-forward-column (length (car rectangle)))
			      (picture-move-down (1- (length rectangle)))
			      (point)))))
    (push-mark)
    (insert-rectangle rectangle)))

(defun picture-current-line ()
  "Return the vertical position of point.  Top line is 1."
  (+ (count-lines (point-min) (point))
     (if (= (current-column) 0) 1 0)))

(defun picture-draw-rectangle (start end)
  "Draw a rectangle around region from START to END."
  (interactive "*r")                    ; start will be less than end
  (let* ((sl     (picture-current-line))
         (sc     (current-column))
         (pvs    picture-vertical-step)
         (phs    picture-horizontal-step)
         (c1     (progn (goto-char start) (current-column)))
         (r1     (picture-current-line))
         (c2     (progn (goto-char end) (current-column)))
         (r2     (picture-current-line))
         (right  (max c1 c2))
         (left   (min c1 c2))
         (top    (min r1 r2))
         (bottom (max r1 r2)))
    (goto-char (point-min))
    (forward-line (1- top))
    (move-to-column left t)
    (picture-update-desired-column t)

    (picture-movement-right)
    (picture-insert picture-rectangle-ctl 1)
    (picture-insert picture-rectangle-h (- right picture-desired-column))

    (picture-movement-down)
    (picture-insert picture-rectangle-ctr 1)
    (picture-insert picture-rectangle-v (- bottom (picture-current-line)))

    (picture-movement-left)
    (picture-insert picture-rectangle-cbr 1)
    (picture-insert picture-rectangle-h (- picture-desired-column left))

    (picture-movement-up)
    (picture-insert picture-rectangle-cbl 1)
    (picture-insert picture-rectangle-v (- (picture-current-line) top))

    (picture-set-motion pvs phs)
    (goto-char (point-min))
    (forward-line (1- sl))
    (move-to-column sc t)))


;; Picture Keymap, entry and exit points.

(defalias 'picture-delete-char 'delete-char)

(defvar-keymap picture-mode-map
  :doc "Keymap used in `picture-mode'."
  :full t
  "<remap> <self-insert-command>"           #'picture-self-insert
  "<remap> <completion-separator-self-insert-command>" #'picture-self-insert
  "<remap> <completion-separator-self-insert-autofilling>" #'picture-self-insert
  "<remap> <forward-char>"                  #'picture-forward-column
  "<remap> <right-char>"                    #'picture-forward-column
  "<remap> <backward-char>"                 #'picture-backward-column
  "<remap> <left-char>"                     #'picture-backward-column
  "<remap> <delete-char>"                   #'picture-clear-column
  ;; There are two possibilities for what is normally on DEL.
  "<remap> <backward-delete-char-untabify>" #'picture-backward-clear-column
  "<remap> <delete-backward-char>"          #'picture-backward-clear-column
  "<remap> <kill-line>"                     #'picture-clear-line
  "<remap> <open-line>"                     #'picture-open-line
  "<remap> <newline>"                       #'picture-newline
  "<remap> <newline-and-indent>"            #'picture-duplicate-line
  "<remap> <next-line>"                     #'picture-move-down
  "<remap> <previous-line>"                 #'picture-move-up
  "<remap> <move-beginning-of-line>"        #'picture-beginning-of-line
  "<remap> <move-end-of-line>"              #'picture-end-of-line
  "<remap> <mouse-set-point>"               #'picture-mouse-set-point
  "C-c C-d"     #'picture-delete-char
  "TAB"         #'picture-tab
  "M-TAB"       #'picture-tab-search
  "C-c TAB"     #'picture-set-tab-stops
  "C-c C-k"     #'picture-clear-rectangle
  "C-c C-w"     #'picture-clear-rectangle-to-register
  "C-c C-y"     #'picture-yank-rectangle
  "C-c C-x"     #'picture-yank-rectangle-from-register
  "C-c C-r"     #'picture-draw-rectangle
  "C-c C-c"     #'picture-mode-exit
  "C-c C-f"     #'picture-motion
  "C-c C-b"     #'picture-motion-reverse
  "C-c <"       #'picture-movement-left
  "C-c >"       #'picture-movement-right
  "C-c ^"       #'picture-movement-up
  "C-c ."       #'picture-movement-down
  "C-c `"       #'picture-movement-nw
  "C-c '"       #'picture-movement-ne
  "C-c /"       #'picture-movement-sw
  "C-c \\"      #'picture-movement-se
  "C-c <left>"  #'picture-movement-left
  "C-c <right>" #'picture-movement-right
  "C-c <up>"    #'picture-movement-up
  "C-c <down>"  #'picture-movement-down
  "C-c <home>"  #'picture-movement-nw
  "C-c <prior>" #'picture-movement-ne
  "C-c <end>"   #'picture-movement-sw
  "C-c <next>"  #'picture-movement-se)

(defcustom picture-mode-hook nil
  "If non-nil, its value is called on entry to Picture mode.
Picture mode is invoked by the command \\[picture-mode]."
  :type 'hook)

(defvar picture-mode-old-local-map)
(defvar picture-mode-old-mode-name)
(defvar picture-mode-old-major-mode)
(defvar picture-mode-old-truncate-lines)

;;;###autoload
(defun picture-mode ()
  "Switch to Picture mode, in which a quarter-plane screen model is used.
\\<picture-mode-map>
Printing characters replace instead of inserting themselves with motion
afterwards settable by these commands:

 Move left after insertion:            \\[picture-movement-left]
 Move right after insertion:           \\[picture-movement-right]
 Move up after insertion:              \\[picture-movement-up]
 Move down after insertion:            \\[picture-movement-down]

 Move northwest (nw) after insertion:  \\[picture-movement-nw]
 Move northeast (ne) after insertion:  \\[picture-movement-ne]
 Move southwest (sw) after insertion:  \\[picture-movement-sw]
 Move southeast (se) after insertion:  \\[picture-movement-se]

 Move westnorthwest (wnw) after insertion:  \\[universal-argument] \\[picture-movement-nw]
 Move eastnortheast (ene) after insertion:  \\[universal-argument] \\[picture-movement-ne]
 Move westsouthwest (wsw) after insertion:  \\[universal-argument] \\[picture-movement-sw]
 Move eastsoutheast (ese) after insertion:  \\[universal-argument] \\[picture-movement-se]

The current direction is displayed in the mode line.  The initial
direction is right.  Whitespace is inserted and tabs are changed to
spaces when required by movement.  You can move around in the buffer
with these commands:

 Move vertically to SAME column in previous line: \\[picture-move-down]
 Move vertically to SAME column in next line:     \\[picture-move-up]
 Move to column following last
  non-whitespace character:                       \\[picture-end-of-line]
 Move right, inserting spaces if required:        \\[picture-forward-column]
 Move left changing tabs to spaces if required:   \\[picture-backward-column]
 Move in direction of current picture motion:     \\[picture-motion]
 Move opposite to current picture motion:         \\[picture-motion-reverse]
 Move to beginning of next line:                  \\[next-line]

You can edit tabular text with these commands:

 Move to column beneath (or at) next interesting
  character (see variable `picture-tab-chars'):   \\[picture-tab-search]
 Move to next stop in tab stop list:              \\[picture-tab]
 Set tab stops according to context of this line: \\[picture-set-tab-stops]
   (With ARG, resets tab stops to default value.)
 Change the tab stop list:                        \\[edit-tab-stops]

You can manipulate text with these commands:
 Clear ARG columns after point without moving:    \\[picture-clear-column]
 Delete char at point:                            \\[picture-delete-char]
 Clear ARG columns backward:                      \\[picture-backward-clear-column]
 Clear ARG lines, advancing over them:            \\[picture-clear-line]
  (the cleared text is saved in the kill ring)
 Open blank line(s) beneath current line:         \\[picture-open-line]

You can manipulate rectangles with these commands:
  Clear a rectangle and save it:                  \\[picture-clear-rectangle]
  Clear a rectangle, saving in a named register:  \\[picture-clear-rectangle-to-register]
  Insert currently saved rectangle at point:      \\[picture-yank-rectangle]
  Insert rectangle from named register:           \\[picture-yank-rectangle-from-register]
  Draw a rectangular box around mark and point:   \\[picture-draw-rectangle]
  Copies a rectangle to a register:               \\[copy-rectangle-to-register]
  Undo effects of rectangle overlay commands:     \\[undo]

You can return to the previous mode with \\[picture-mode-exit], which
also strips trailing whitespace from every line.  Stripping is suppressed
by supplying an argument.

Entry to this mode calls the value of `picture-mode-hook' if non-nil.

Note that Picture mode commands will work outside of Picture mode, but
they are not by default assigned to keys."
  (interactive)
  (if (eq major-mode 'picture-mode)
      (error "You are already editing a picture")
    (setq-local picture-mode-old-local-map (current-local-map))
    (use-local-map picture-mode-map)
    (setq-local picture-mode-old-mode-name mode-name)
    (setq-local picture-mode-old-major-mode major-mode)
    (setq major-mode 'picture-mode)
    (setq-local picture-killed-rectangle nil)
    (setq-local tab-stop-list (default-value 'tab-stop-list))
    (setq-local picture-tab-chars (default-value 'picture-tab-chars))
    (make-local-variable 'picture-vertical-step)
    (make-local-variable 'picture-horizontal-step)
    (setq-local picture-mode-old-truncate-lines truncate-lines)
    (setq truncate-lines t)
    (picture-set-motion 0 1)

    ;; edit-picture-hook is what we used to run, picture-mode-hook is in doc.
    (run-hooks 'edit-picture-hook 'picture-mode-hook)
    (message "Type %s in this buffer to return it to %s mode."
	     (substitute-command-keys "\\[picture-mode-exit]")
	     picture-mode-old-mode-name)))

;;;###autoload
(defalias 'edit-picture 'picture-mode)

(defun picture-mode-exit (&optional nostrip)
  "Undo `picture-mode' and return to previous major mode.
With NOSTRIP omitted or nil, strip whitespace from end of every line
  in Picture buffer; otherwise, just return to previous mode.
Interactively, NOSTRIP is the prefix argument, and defaults to nil.
Runs `picture-mode-exit-hook' at the end."
  (interactive "P")
  (if (not (eq major-mode 'picture-mode))
      (error "You aren't editing a Picture")
    (if (not nostrip) (delete-trailing-whitespace))
    (setq mode-name picture-mode-old-mode-name)
    (use-local-map picture-mode-old-local-map)
    (setq major-mode picture-mode-old-major-mode)
    (kill-local-variable 'tab-stop-list)
    (setq truncate-lines picture-mode-old-truncate-lines)
    (force-mode-line-update)
    (run-hooks 'picture-mode-exit-hook)))

(provide 'picture)

;;; picture.el ends here