Re: What is `image-compute-scaling-factor' for?

[Evgeny Zajcev <lg.zevlg@gmail.com>]

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пт, 25 дек. 2020 г. в 08:18, Lars Ingebrigtsen <larsi@gnus.org>:

> Evgeny Zajcev <lg.zevlg@gmail.com> writes:
>
> > Lars, could you please elaborate the logic in the
> > `image-compute-scaling-factor'.  As I understand, it means "the larger
> > font you have, the larger image you get"?  But why?  I use large fonts
> > (say 30 pixels in width), in 1920x1080 screen,
>
> (/ 1920.0 30) => 64.0
>
> You only have 64 characters in width?
>
> > and I'm totally ok with scale factor 1 for images, but `auto'
> > image-scaling-factor gives me 3 as default scale.  This results in
> > very large images.
>
> The idea is that images scale somewhat along the lines of your
> characters, so if you're reading text with interspersed images (for
> instance, math equations), they'll be approximately the same size,
> whether you're using a HiDPI display or not.  As a heuristic, that seems
> to work surprisingly well.
>
>
But the problem is that this scaling logic is applied globally to all the
images used inside Emacs, not only to some math equations.

I really can't get how this default behaviour could be ok, see screenshots:
http://lgarc.narod.ru/pics/screenshot-scale.png

For example by default Emacs dashboard looks like:
http://lgarc.narod.ru/pics/screenshot-scale-dashboard.png

For me, this looks surprisingly bad

(This is based on the assumption that your image resources come from a
> non-HiDPI world, though.)
>
> If you don't want that, then set the scaling factor to whatever you
> want.
>
> > For better `auto' scaling we should consider the physical size of the
> > display and its resolution (that is called DPI I think?) not the size
> > of the font.  But probably this info is not always available.  If we
> > have that DPI info, we can then calculate `auto' scale factor using
> > "typical DPI" (where images looks ok).  Something like:
>
> The problem is that the functions that say how big a screen are are
> often incorrect.  I've got a 14" 3840x2160 screen:
>
> (display-mm-height)
> => 571
>
> It's not half a meter high, I can assure you.
>

So, what the value you have now as return for (image-compute-scaling-factor
'auto) ?

With code I've provided you hit into typical DPI (your DPI=96 < 100) and
get scaling factor 1.

-- 
lg

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