Re: High-res Customize icons

[YAMAMOTO Mitsuharu]

On Wed, 28 Oct 2020 04:17:37 +0900,
Yuan Fu wrote:
>
> I dug a bit further and it seems to do with Cocoa on Mac. On other engines 
> the resolution is simply the resolution of the monitor, but Cocoa add an 
> abstraction layer and the resolution an applications detects aren’t the 
> actual physical resolution.
> 
> So for high-res icons we want to simply use the @2x image on Linux and use 
> @2x image but with :scale 0.5 on Cocoa. If we use normal image on high-res 
> monitor, the image is too small on Linux, and if we are on Cocoa, the image 
> is blurry.
> 
> To detect high-res screens on other platforms, we currently have a function 
> that measures the pixel height of a default line: if it’s greater than 15 
> pixels, we consider the screen high-res and find-image will scale the 
> returned image by :scale 2.
> 
> Cocoa provides an API for querying the scaling factor, if it is 2, we should 
> load the @2x image and add :scale 0.5.
> 
> It’s kind of a mess. What do you think?
>
> How about exposing that Cocoa API to lisp and handle accordingly in 
> find-image? Some thing like:
> 
> (let (img)
>   (if (eq (window-system) 'ns)
>       ;; Cocoa
>       (let ((pixel-scaling-factor (ns-scaling-factor)))
>         (if (> pixel-scaling-factor 1.0)
>             (append (find-2x-image) '(:scale 0.5))
>           (find-normal-image)))
>     ;; Other
>     (let ((image-scaling-factor (image-compute-scaling-factor
>                                  image-scaling-factor)))
>       (if (> image-scaling-factor 2)
>           (append (find-2x-image) '(:scale 2))
>         (find-normal-image)))))


The Mac port (not the NS port) has supported @2x images since 2012 at
the C level as opposed to the Lisp level.  It also automatically
re-renders images in resolution-independent formats such as SVG or PDF
in reaction to the frame movement from a Retina display to a
non-Retina one, for example.  You might want to look at the
corresponding part of the Info document for the Mac port:

https://bitbucket.org/mituharu/emacs-mac/src/dfb5869abf8f6892e928042e9f8221f8435a0dcb/doc/emacs/macport.texi#lines-446

Althogh the backing scale factor information is not necessary at the
Lisp level for the automatic bitmap selection for the Mac port, it is
available via display-monitor-attributes-list (or
frame-monitor-attributes if you want to specify the frame to be
examined) as it is considered as a monitor-specific property.

    (pp (display-monitor-attributes-list))
    (((geometry 0 0 2560 1440)
      (workarea 0 23 2560 1337)
      (mm-size 599 340)
      (frames #<frame Emacs@YAMAMOTO-no-iMac-5K.local 0x7faa96927200>)
      (name . "iMac")
      (metal-device-name . "AMD Radeon R9 M380")
      (backing-scale-factor . 2))
     ((geometry 2560 0 1920 1200)
      (workarea 2560 23 1920 1177)
      (mm-size 493 311)
      (frames)
      (name . "Cinema HD")
      (metal-device-name . "AMD Radeon R9 M380")
      (backing-scale-factor . 1)))

                                     YAMAMOTO Mitsuharu
                                mituharu@math.s.chiba-u.ac.jp