Re: Suggestion: A fringe indicator that shows the last/first line before scrolling

["David De La Harpe Golden" <david.delaharpe.golden@gmail.com>]

On 29/02/2008, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
> Not really.  It just means it will only work 99%.
>

Quite different 99% approach sketched below, uses our old friend the
idle timer, to show the window position in the fringe with a 2 sec
lag. Works better than I expected.

I think I'm not quite getting something though: why are fringe marks
"replacing" display properties (i.e. if a character pos has a fringe
display property, the character isn't displayed)? - that leads to my
use of before and after string properties.   I wanted to hide the
fringe marks conditionally while they align with the real window-start
and window-end (they're not useful then), but because the fringe marks
are "replacing", the magic "when" conditional display property is
unsuitable for that.   If before/after-string properties supported
"when" or fringe marks weren't "replacing" display properties....


(defface window-pos-fringe
  '((t (:foreground "cyan")))
  "Window pos fringe face"
  :group 'scrolling)

(defvar show-old-window-pos-overlay
   (make-overlay (window-start) (window-end)))

(overlay-put show-old-window-pos-overlay 'before-string
	     (concat
	      (propertize "[" 'display
			  (list 'left-fringe 'top-left-angle
				'window-pos-fringe))
	      (propertize "[" 'display
			  (list 'right-fringe 'top-right-angle
				'window-pos-fringe))))

(overlay-put show-old-window-pos-overlay 'after-string
	     (concat
	      (propertize "]" 'display
			  (list 'left-fringe 'bottom-left-angle
				'window-pos-fringe))
	      (propertize "]" 'display
			  (list 'right-fringe
				'bottom-right-angle
				'window-pos-fringe))))


(defun update-window-pos-overlay  ()
  (move-overlay show-old-window-pos-overlay
		(window-start)
		(- (window-end) 1)
		(window-buffer))
  (redisplay))

(run-with-idle-timer 2 t 'update-window-pos-overlay)