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Point to Pixel


From: Patrick
Subject: Point to Pixel
Date: Wed, 8 Jun 2005 15:15:55 -0500

On windows gnu emacs (~21.3) this code will return the pixel-position
of the current point! (or at least, within a few pixels) Returns values
in form (x . y).

I wanted this feature and couldn't find it... all I found were posts in
lists also asking for the feature, with people denying it could be done
in elisp. Well, that is not true! ;)

I believe this should work in Xemacs and on other operating systems and
recent emacs versions.

I am currently using it to display an "intellisense"-like tooltip.
Which, on windows, gnu emacs has no tooltip, so I am executing a little
python app instead which handles the tooltip for me (via wx libraries).
Works very nice.


; helper func
(defun get-param-safe (s)
  "Sometimes frame-paramater returns values of (+ -4)"
  (let ((left (frame-parameter nil s)))
    (if (listp left) (cadr left) left)))


; this is it
(defun point-to-pixel ()
  "Converts the position of the current point to pixel
   coordinates relative to the screen (i.e. window manager)."
  (let ((left (car (window-edges)))
        (top (cadr (window-edges)))
        (point-left (- (point) (point-at-bol)))
        (point-top  (point)))
    (let ((x (+ (* (frame-char-width) left)  ; x =
                (* (frame-char-width) point-left)
                (get-param-safe 'left)))
          (y (+ (* (frame-char-height)       ; y =
                   (+ top
                      (count-lines (window-start) (point))))
                (get-param-safe 'top))))
      (cons x y))))




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