elisp: Abstract Display Example
37.20.2 Abstract Display Example
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Here is a simple example using functions of the ewoc package to
implement a “color components” display, an area in a buffer that
represents a vector of three integers (itself representing a 24-bit RGB
value) in various ways.
(setq colorcomp-ewoc nil
colorcomp-data nil
colorcomp-mode-map nil
colorcomp-labels ["Red" "Green" "Blue"])
(defun colorcomp-pp (data)
(if data
(let ((comp (aref colorcomp-data data)))
(insert (aref colorcomp-labels data) "\t: #x"
(format "%02X" comp) " "
(make-string (ash comp -2) ?#) "\n"))
(let ((cstr (format "#%02X%02X%02X"
(aref colorcomp-data 0)
(aref colorcomp-data 1)
(aref colorcomp-data 2)))
(samp " (sample text) "))
(insert "Color\t: "
(propertize samp 'face
`(foreground-color . ,cstr))
(propertize samp 'face
`(background-color . ,cstr))
"\n"))))
(defun colorcomp (color)
"Allow fiddling with COLOR in a new buffer.
The buffer is in Color Components mode."
(interactive "sColor (name or #RGB or #RRGGBB): ")
(when (string= "" color)
(setq color "green"))
(unless (color-values color)
(error "No such color: %S" color))
(switch-to-buffer
(generate-new-buffer (format "originally: %s" color)))
(kill-all-local-variables)
(setq major-mode 'colorcomp-mode
mode-name "Color Components")
(use-local-map colorcomp-mode-map)
(erase-buffer)
(buffer-disable-undo)
(let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
(color-values color))))
(ewoc (ewoc-create 'colorcomp-pp
"\nColor Components\n\n"
(substitute-command-keys
"\n\\{colorcomp-mode-map}"))))
(set (make-local-variable 'colorcomp-data) data)
(set (make-local-variable 'colorcomp-ewoc) ewoc)
(ewoc-enter-last ewoc 0)
(ewoc-enter-last ewoc 1)
(ewoc-enter-last ewoc 2)
(ewoc-enter-last ewoc nil)))
This example can be extended to be a color selection widget (in other
words, the “controller” part of the “model–view–controller” design
paradigm) by defining commands to modify ‘colorcomp-data’ and to finish
the selection process, and a keymap to tie it all together conveniently.
(defun colorcomp-mod (index limit delta)
(let ((cur (aref colorcomp-data index)))
(unless (= limit cur)
(aset colorcomp-data index (+ cur delta)))
(ewoc-invalidate
colorcomp-ewoc
(ewoc-nth colorcomp-ewoc index)
(ewoc-nth colorcomp-ewoc -1))))
(defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
(defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
(defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
(defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
(defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
(defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
(defun colorcomp-copy-as-kill-and-exit ()
"Copy the color components into the kill ring and kill the buffer.
The string is formatted #RRGGBB (hash followed by six hex digits)."
(interactive)
(kill-new (format "#%02X%02X%02X"
(aref colorcomp-data 0)
(aref colorcomp-data 1)
(aref colorcomp-data 2)))
(kill-buffer nil))
(setq colorcomp-mode-map
(let ((m (make-sparse-keymap)))
(suppress-keymap m)
(define-key m "i" 'colorcomp-R-less)
(define-key m "o" 'colorcomp-R-more)
(define-key m "k" 'colorcomp-G-less)
(define-key m "l" 'colorcomp-G-more)
(define-key m "," 'colorcomp-B-less)
(define-key m "." 'colorcomp-B-more)
(define-key m " " 'colorcomp-copy-as-kill-and-exit)
m))
Note that we never modify the data in each node, which is fixed when
the ewoc is created to be either ‘nil’ or an index into the vector
‘colorcomp-data’, the actual color components.
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elisp: Abstract Display Functions
elisp: Abstract Display