Yes it's too late now.
When it is added later I would prefer having a setting that is simply DPI-depending. When I set e.g. icon size to 24 and I set DPI to e.g. 144 the icon would be drawn as 36px, when I set the DPI to 192 it is drawn as 48px.
This would not require a new setting and - if any - minimal changes to the UI.
Button-bar icon size specefied for a resolution
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