Small Emacs ASCII animation

aa.el

;;(require 'drawille)
(load-file "drawille.el")

(defvar aa-pixel 1
  "A one in the matrix represents a set pixel")

(defun aa-matrix-set (matrix col row elt)
  "Helper to set values in the matrix"
  (let ((grid-row (aref matrix row)))
    (aset grid-row col elt)))

(defun aa-create-circle (matrix start end stepsize radius &optional xshift yshift)
  (dolist (x (number-sequence start end stepsize))
    (aa-matrix-set matrix
                   (floor (+ radius (or xshift 0) (* radius (cos (radians-to-degrees x)))))
                   (floor (+ radius (or yshift 0) (* radius (sin (radians-to-degrees x)))))
                   aa-pixel)))


(defun aa-get-circle-frames (anim-length)
  "Creating the animation frames"
  (interactive)
  (let* ((i 1)
         (dr 1)
         (radius 2)
         matrix
         frames)
    (while (<= i anim-length)
      (setq radius (+ dr radius))
      ;; (+ radius (* radius cos/sin...))
      (setq vheight (* 2 radius))
      (setq vwidth (* 2 radius))
      (message "Creating frame %s of %s" i anim-length)
      ;; reinitialize an empty matrix
      (setq matrix
            (let ((grid (make-vector vheight nil)))
              (dotimes (row vheight)
                (aset grid row (make-vector vwidth 0)))
              grid))
      (aa-create-circle matrix 2 360 8 radius)
      (aa-create-circle matrix 16 360 8 (- radius 1) 1 1)
      (aa-create-circle matrix 32 360 8 (- radius 2) 2 2)

      (add-to-list 'frames (drawille-matrix matrix) t)
      (setq i (1+ i)))
    frames))


(defun aa-init-draw-buffer ()
  "Initialize the drawing buffer"
  (buffer-disable-undo)
  (setq cursor-type nil))


(defun aa-animate-circle (anim-length)
  "Start the animation"
  (let (frames)
    (setq frames (aa-get-circle-frames anim-length))
    (switch-to-buffer (get-buffer-create "*draw*"))
    (while t
      (dolist (frame frames)
        (aa-init-draw-buffer)
        (erase-buffer)
        (insert frame)
        (put-text-property (point-min) (point-max) 'face '(foreground-color . "#8a2be2"))
        (sit-for 0.1)))))


(aa-animate-circle 30)