After thinking about it, I am wondering if the current behavior of
'window-lines-pixel-dimensions' is correct ?
As user of the function I do not expect the function to count glyphs that
are inserted by redisplay only "for its own purpose",
glyphs that are invisible and non-existent for the end user.
IMHO, for an empty line,  'window-lines-pixel-dimensions' should return the
width 0.
A line with X characters should have the width of all thoses characters.
I see that 'window-largest-empty-rectangle' uses this function, the widths
of the rectangles it returns are smaller than they really are.

I think it makes sense to change this behavior and make
'window-lines-pixel-dimensions' not counting these "redisplay only" glyphs.
Thus, there would be no need for a new argument to the function.

> Agreed.  Sébastien can you try to show "that using the glyph matrices
> is much faster"?

I tested the following code:

```
(defmacro time (&rest forms)
  (let ((t1 (make-symbol "t1")))
    `(let (,t1)
       (redisplay t)
       (setq ,t1 (current-time))
       ,@forms
       (float-time (time-since ,t1)))))

(defun test1 nil
  (window-lines-pixel-dimensions nil nil nil t))

(defun test2 nil
  (save-excursion
    (goto-char (window-start))
    (let ((index 1)
          (height (window-body-height)))
      (while (<= index height)
        (window-text-pixel-size nil (line-beginning-position index)
(line-end-position index))
        (setq index (1+ index))
        ))))
```

`(time (test1))` returns 0.000004869
`(time (test2))` returns 0.00376






Le sam. 9 nov. 2019 à 02:27, martin rudalics <rudalics@gmx.at> a écrit :

>  > In general, functions that use only the glyph matrices have a
>  > significant disadvantage in that they will fail when display is not up
>  > to date, something that can happen out of control of a Lisp program
>  > that calls the function.  So I very much prefer window-text-pixel-size
>  > to an alternative that uses the glyph matrices.  If we find that using
>  > the glyph matrices is much faster, then I'd prefer to fix
>  > window-text-pixel-size to use the glyph matrices when possible, and
>  > otherwise fall back to its current method.  See move-point-visually
>  > for one example of how this can be done.
>
> Agreed.  Sébastien can you try to show "that using the glyph matrices
> is much faster"?
>
> martin
>
>