39.20.2 Abstract Display Example

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) ?#) "

")) (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)) "

")))) (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 "

Color Components



" (substitute-command-keys "

\\{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))