On Sat, Jan 08, 2022 at 11:38:47PM +0100, Jan Engelhardt wrote: > > On Saturday 2022-01-08 20:57, Alan Stern wrote: > > >The screen resolution on my laptop is not reported accurately. Here's > >an extract from the output of xdpyinfo (under Xwayland): > > > >screen #0: > > dimensions: 3200x1800 pixels (847x476 millimeters) > > resolution: 96x96 dots per inch > > > >The number of pixels is correct, but the size and resolution values > >smack of a bogus default. > > The way I remember it: > > 1. Xorg(!) would read EDID once on startup, and set the DPI value > based on it. // Or you have your environment set to a fixated > DPI value, then that is used. > > 2. millimeter numbers reported afterwards through X are not > EDID-based, but simply area size divided by DPI. > > As such, I have, for example: > > dimensions: 1920x1080 pixels (508x286 millimeters) > resolution: 96x96 dots per inch > > on both a 12" and a 13" laptop. > > Now, the DPI value has been fixated at 96 recently again - > https://www.phoronix.com/scan.php?page=news_item&px=X.Org-Server-21.1.2 > because, in summary, you cannot determine a sensible global DPI > value if a system has two or more monitors of different pixel > density. Either the font is too small or too big for either screen. > > (And the only way to truly have separate DPI values per monitor > might be a Xinerama-style setup where each monitor is its own > independent X (sub)screen object, hence DISPLAY=":0.0".) > > And Wayland probably just behaves the same as Xorg, for the same > reasons.
Thanks for your help. I wonder if that is really the whole story, though. On systems with a single monitor, why not determine an accurate DPI value? For that matter, on systems with multiple monitors, why not use the DPI value of the first as a global value? It can't be any worse than using 96 DPI for everything. Alan Stern
