.emacs.d/emacs-notes.org

Random Notes on Emacs

• Fractals in Emacs
• Emacs reencode buffers with other encoding

This is a small collection of Emacs related posts and documentation by other authors that I find useful.

Fractals in Emacs

From https://nullprogram.com/blog/2012/09/14/

(defun sierpinski (s)
  (pop-to-buffer (get-buffer-create "*sierpinski*"))
  (fundamental-mode) (erase-buffer)
  (labels ((fill-p (x y)
                   (cond ((or (zerop x) (zerop y)) "0")
                         ((and (= 1 (mod x 3)) (= 1 (mod y 3))) "1")
                         (t (fill-p (/ x 3) (/ y 3))))))
    (insert (format "P1\n%d %d\n" s s))
    (dotimes (y s) (dotimes (x s) (insert (fill-p x y) " "))))
  (image-mode))

(defun mandelbrot ()
  (pop-to-buffer (get-buffer-create "*mandelbrot*"))
  (let ((w 400) (h 300) (d 32))
    (fundamental-mode) (erase-buffer)
    (set-buffer-multibyte nil)
    (insert (format "P6\n%d %d\n255\n" w h))
    (dotimes (y h)
      (dotimes (x w)
        (let* ((cx (* 1.5 (/ (- x (/ w 1.45)) w 0.45)))
               (cy (* 1.5 (/ (- y (/ h 2.0)) h 0.5)))
               (zr 0) (zi 0)
               (v (dotimes (i d d)
                    (if (> (+ (* zr zr) (* zi zi)) 4) (return i)
                      (psetq zr (+ (* zr zr) (- (* zi zi)) cx)
                             zi (+ (* (* zr zi) 2) cy))))))
          (insert-char (floor (* 256 (/ v 1.0 d))) 3))))
    (image-mode)))

Emacs reencode buffers with other encoding

• Use the function revert-buffer-with-coding-system to re-open a buffer in another encoding.
• Customize the variable file-coding-system-alist to control whether certain files should always be opened with a specific encoding.