bug#37689: Fringe pixmaps, widgets, etc. look ridiculously tiny in hidpi screen

[Juri Linkov]

>> I guess it should be possible to do the same to provide x2 scaled bitmaps:
>>
>>   (define-fringe-bitmap 'light-down-arrow [32 32 32 32 32 32 168 112 32] nil 
>> nil 'bottom)
>
> This is indeed a cool workaround if you can override the builtin
> bitmaps.

Actually, this doesn't override the builtin bitmaps.
The name of the builtin bitmap is 'down-arrow',
but this defines a new bitmap 'light-down-arrow'.
You can use any name you want, e.g. 'down-arrow-2x'.

> But anyway it won't address the problem of having different
> frames with different dpis nor the need to expose a "scale factor api"
> to fix not only this but other hidpi-related issues.

Maybe the value of 'fringe-indicator-alist' should be frame-local?
Then depending on the exposed scale-factor, each frame could use
own set of bitmaps defined by frame-local 'fringe-indicator-alist'.

>> Funnily enough, the current fringe bitmaps are too big for me,
>
> Too big as in "twice as big as expected" or in "too big for my taste"?

I use a small 10px font, so the customized bitmaps fit the font size.
So maybe fridge bitmap size should depend on the font size, not scale?