Re: width of propertized string

[David Reitter <david.reitter@gmail.com>]

On 5 Jun 2008, at 20:47, Stefan Monnier wrote:

>> Given a propertized string, how would one find out what its (pixel)
>> dimensions are going to be?
>
> Display it, measure its size.

Tried that (see code below).  This is too slow because we need to  
switch to the temporary buffer.

All of my use cases concern displaying things in the echo area or the  
header line.  Thus, I would want to ignore any font locking and other  
automatically applied properties.

My use cases are:

- adding appropriate spacing and justifying buttons in the header line
- word-wrapping text, primarily in the echo area before displaying it.



(defun visual-pixel-col-at-point ()
  (or
   (car-safe (pos-visible-in-window-p (point) nil 'partial))
   0))


(defun string-pixel-width (text)
   (let ((width))
     (let ((old-buffer (current-buffer)))
	  (with-temp-buffer ;; should be in fundamental-mode
	    ;; this is way too slow.
	    (switch-to-buffer (current-buffer) t)
	    (let ((buffer-undo-list nil) (start (point))
		  (truncate-lines t) (after-change-functions nil))
	      (let ((left (visual-pixel-col-at-point)))
		(insert text)
		(setq width (- (visual-pixel-col-at-point) left)))
	      (delete-region start (point)))
	    (switch-to-buffer old-buffer t)))
       width))