HiDPI is very common nowadays.  Internally Emacs has decent support for
HiDPI displays.  However elisp code, that generates non-svg images don't
have any idea that logical pixel may differ from physical one, resulting in
generating images in low resolution on HiDPI displays.

Emacs internally has a notion about HiDPI displays, such as
`x_get_scale_factor`, maybe expose this function to elisp level, so
packages may utilize it to generate images in highres?

Or `(> (round (/ (display-pixel-height) (/ (display-mm-height) 25.4))) 96)`
is good enough to detect HiDPI displays?

Thanks

-- 
lg