Using Emacs `:stipple` face attribute for drawing bars and other pixel-level features

box-stipple.el

(let ((buf (get-buffer-create "*stipple-box*")))
  (switch-to-buffer-other-window buf)
  (cl-flet  ((srot (s r) (concat (substring s (- r)) (substring s 0 (- r)))))
    (let* ((bar-width 0.3)
           (w (window-font-width))
           (h (window-font-height))
           (rot (indent-bars--stipple-rot w))
           (bsz (round (* bar-width w)))
           (vrot (mod (cadr (window-edges nil t nil t)) h))
           (pad (make-string (- h bsz) ?\s))
           (vpat-top (srot (concat pad (make-string bsz ?.)) vrot))
           (vpat-bot (srot (concat (make-string bsz ?.) pad) vrot))
           (vbar-left (indent-bars--stipple w h rot bar-width 0 "." nil))
           (vbar-right (indent-bars--stipple w h rot bar-width (- 1 bar-width) "." nil))
           (vbar-left-string (propertize " " 'face `(:stipple ,vbar-left)))
           (vbar-right-string (propertize " " 'face `(:stipple ,vbar-right)))
           (row-string (concat vbar-left-string (make-string 28 ?\s) vbar-right-string))
           (hbar-top (indent-bars--stipple w h rot 1. 0. vpat-top nil))
           (hbar-bot (indent-bars--stipple w h rot 1. 0. vpat-bot nil))
           (hbar-top-string (propertize (make-string 30 ?\s) 'face `(:stipple ,hbar-top)))
           (hbar-bot-string (propertize (make-string 30 ?\s) 'face `(:stipple ,hbar-bot))))
      (erase-buffer)
      (insert (concat "\n " hbar-top-string "\n"))
      (dotimes (_ 10) (insert " " row-string "\n"))
      (insert " " vbar-left-string "    This box is drawn       " vbar-right-string "\n")
      (insert " " vbar-left-string "        with :stipple       " vbar-right-string "\n")
      (dotimes (_ 10) (insert " " row-string "\n"))
      (insert " " row-string)
      (insert (concat "\n " hbar-bot-string "\n")))))

This small proof-of-concept shows the use of stipple face attributes to draw both horizontal and vertical lines. It uses functions from indent-bars. Here's how it looks:

Some important points about :stipple:

• Each stipple is a repeating bitmap, which starts at the absolute pixel position of the frame's top-left pixel (behind the margin and fringe) and repeats down and right infinitely.
• The basic idea is to make stipple patterns of the same width and height as characters.
• Setting a face containing a :stipple attribute on some visible characters simply "open up" a window onto that fixed stipple pattern.
• You therefore have to rotate the bitmap byte pattern appropriately to get it to line up. This can be automated on window and text size changes, as indent-bars does.
• For drawing horizontal lines, you need to perform a similar rotation of the stipple list, based on the vertical window pixel offset into the frame. window-edges can tell you these pixel offsets.
• This idea only works if line width and height are constant, so images, emoji, variable width/height fonts, etc. will make patterns unstable.

You can easily create a few faces that have :stipple set, apply them to various characters in a buffer, and use face-remapping-alist to quickly update colors, etc. In principle with enough care you could draw anything with a stipple pattern.