Re: Scaling stuff for high dpi screens

[asjo@koldfront.dk (Adam Sjøgren)]

asjo@koldfront.dk (Adam Sjøgren) writes:

> Thanks a bunch - now I just need to figure out how to extract the
> current dpi from X, and adjust the magnitude value on the fly.

I stole some code from from
https://github.com/bodil/emacs.d/blob/master/bodil-theme.el and adapted
it a little; so this calls xrandr to find the dpi by grabbing the
vertical pixels and the vertical mm size from the output:

  (defun get-x11-dpi ()
    (let ((xrandr
           (with-output-to-string
             (call-process "xrandr" nil standard-output))))
      (string-match "\\(.+\\) connected primary \\(.+\\)x.+ (.+) \\(.+\\)mm x .+mm" xrandr)
      (when (not (match-string 2 xrandr))
        (string-match "\\(.+\\) connected \\(.+\\)x.+ (.+) \\(.+\\)mm x .+mm" xrandr))
      (if (match-string 2 xrandr)
          (let ((pixels (string-to-number (match-string 2 xrandr)))
                (phys (string-to-number (match-string 3 xrandr))))
            (round (/ pixels (/ phys 25.6))))
        96)))

And I use this in a hook, to set a frame parameter with the
magnification I want - I am going simple here - if the dpi is above 100,
I want double up:
        
  (add-hook 'after-make-frame-hook
            '(lambda (new-frame)
               (set-frame-parameter new-frame 'image-dpi-scale-magnitude (if (> (get-x11-dpi) 100) 2.0 1.0))))

I then use Katsumi-san's two defadvices, where I have changed the
magnitude line to grab the frame parameter, like this:
               
      (let* ((magnitude (frame-parameter nil 'image-dpi-scale-magnitude))

For some reason I don't quite understand, it seems that the
hook/get-x11-dpi works inconsistently, so basically I have to evaluate
the set-frame-paremeter part manually a couple of times for it to work,
which I don't understand, but other than that, it is a good step
forward.

Thanks again for the advice!


  :-),

    Adam

-- 
 "Tell them to give it to Donovan."                           Adam Sjøgren
                                                         asjo@koldfront.dk