Jan Kleks composed on 2017-04-07 22:01 (UTC+0200):
2017-04-07 6:03 GMT+02:00 Felix Miata composed:
Konq's KHTML is the only remaining web browser engine capable of rendering physical sizes specified by legacy CSS accurately. The physical CSS units cm, mm, in, etc. were changed in the CSS3 specification to be logical sizes. When a display's physical density is matched to logical density by the server, Konq displays physical units accurately at their actual physical sizes. With other web browsers, this is only possible if the physical display density is 96 DPI (uncommon to say the least) and the server's default logical density of 96 DPI is retained.
Recent Gecko browsers do have the capability of rendering at accurate physical sizes when physical and logical density match, but only by using proprietary CSS which doesn't exist in legacy CSS.
http://fm.no-ip.com/Auth/dpi-screen-window.html is a simple means to confirm the foregoing.
So maybe the old KHTML engine could be transformed into the "legacy mode"?
Maybe do as Konq 4 & 5 do, make it switchable.
Konq 4 offers KHTML and WebKit.
Konq 5 offers KHTML and (QT's) WebEnginePart (aka Blink, aka WebKit fork used by Chromium). http://fm.no-ip.com/SS/KDE/konq5Engines.jpg