bug#54688: 29.0.50; Sliced image in margin looks bad

[dalanicolai <dalanicolai@gmail.com>]

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(Once more using reply-all)

Playing around with :ascent, makes possible to keep the line-pixel-height
fixed.

So in the following I simply use `insert-image`. Without the :ascent, the
'line-pixel-height' increases when inserting another character. With the
:ascent it is possible to reduce this 'increase'. For me the increase is 0
when I use an ascent value of 80.
(below the used code)

(with-current-buffer (get-buffer-create "test")
  (setq left-margin-width 5)
  (insert-image (svg-image (let* ((ph (line-pixel-height))
                                  (size ph)
                                  (svg (svg-create size size)))
                             (svg-circle svg ph ph ph :fill "red")
                             svg)
                           :ascent 80))
  (switch-to-buffer (current-buffer)))

On Sun, 3 Apr 2022 at 12:54, Eli Zaretskii <eliz@gnu.org> wrote:

> > From: dalanicolai <dalanicolai@gmail.com>
> > Date: Sun, 3 Apr 2022 12:33:01 +0200
> > Cc: 54688@debbugs.gnu.org
> >
> > Thank you for the quick reply. However, the height of the image,
> > (* 2 (line-pixel-height)), is equal to twice the `default-font-height`
> > (the 'line-pixel-height' and 'default-font-height' are equal, here both
> > 17).
> >
> > So before I add the character after the image, (line-pixel-height)
> > returns 17. But when I insert a character after it (with
> > 'default-font-height' is 17), the `line-pixel-height` increases to
> > 22. So I am not sure how to not let the line height increase.
> > I will try to play a little with the :ascent value.
>
> Images can also have margins:
>
>   int
>   image_ascent (struct image *img, struct face *face, struct glyph_slice
> *slice)
>   {
>     int height;
>     int ascent;
>
>     if (slice->height == img->height)
>       height = img->height + img->vmargin;
>     else if (slice->y == 0)
>       height = slice->height + img->vmargin;
>     else
>       height = slice->height;
>
> Maybe those make the difference?
>
> In any case, once I add a character, the line height grows, which
> tells us some vertical dimension somewhere is unaccounted for.
>

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