Re: Mechanism to scale SVG images when default face height changes?

[Jimmy Yuen Ho Wong <wyuenho@gmail.com>]

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On Mon, Sep 18, 2023 at 9:53 PM Alan Third <alan@idiocy.org> wrote:

> On Mon, Sep 18, 2023 at 08:55:55PM +0100, Jimmy Yuen Ho Wong wrote:
> > On Mon, Sep 18, 2023 at 8:37 PM Alan Third <alan@idiocy.org> wrote:
> >
> > > On Mon, Sep 18, 2023 at 08:10:59PM +0100, Jimmy Yuen Ho Wong wrote:
> > > > Ah, I was looking at
> > > >
> > >
> https://www.gnu.org/software/emacs/manual/html_node/elisp/Pixel-Specification.html
> > > ,
> <snip>
> > >
> > > I suppose you could calculate the number of ems required by
> > > doing something like...
> > >
> > >       ((/ (- font-px-size 1) font-px-size) . 'em)
> > >
> > > But while that would scale on demand, it wouldn't scale properly
> > > because the calculation is done before the user changes the font size.
> > >
> > > I can't think of any way round it, or even any practical way to extend
> > > the current mechanism.
> > >
> > >
> > Sad face :(. I suppose what I'm really looking for is to extend the pixel
> > specification mini language to support something like CSS' calc()
> > <https://developer.mozilla.org/en-US/docs/Web/CSS/calc> function, where
> it
> > can do arithmetic on both relative and absolute units.
> >
> > Is that possible?
>
> I didn't actually know about the pixel specification language before
> now. It seems to me like it would make sense to teach the image code
> to understand it too and add ems to it, but since I know nothing about
> it I can't say if that's practical or not.
>
> > For my specific purpose, having `:margin` to support
> > floating point em will also suffice, but that doesn't seem to work at the
> > moment.
>
> Indeed, this would actually be quite simple, but it won't help you now
> as it won't be available until Emacs 30.
>
> All I can suggest for compatibility with current versions of Emacs is
> to wrap the SVG's within other SVGs. We do this internally in Emacs to
> implement vector scaling and you could probably do something similar,
> although I'm not sure exactly how much control you could get from it.
>
> For example, you can do something like:
>
> <svg xmlns:xlink="http://www.w3.org/1999/xlink"
>  xmlns:xi="http://www.w3.org/2001/XInclude"
>  width="1em" height="1em" preserveAspectRatio="none">
>   <xi:include href="data:image/svg+xml;base64,<base64 encoded SVG data>">
>   </xi:include>
> </svg>
>
> It should be possible to scale down the embedded image to leave a gap
> around it, but I'd have to go and investigate how to do it.
>
> I recommend base64 encoding the SVG data as shown above, because
> directly embedding the SVG text can be problematic unless it's very
> simple.
> --
> Alan Third
>

Thank you! I'll report back once I've played around with SVG wrappers.

Thanks

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