Re: HiDPI and fractional scaling

[Alexander Larsson <alexl redhat com>]

On mån, 2014-02-03 at 09:27 +0000, Loïc Minier wrote:
> On Mon, Feb 03, 2014, Alexander Larsson wrote:
> [...]
> > Also, the multi-monitor situation wrt hidpi is essentially unfixable
> > on X11.
>
> Would you have details or pointers on this part?  (We'll have X around
> for many years to come, at least to support legacy apps, so we can't
> only rely on Wayland etc. to fix this class of issues.)

Well, the way scaling works on X is that we set a global value for the
scale factor, and all apps just render that much larger. It is
impossible for an X app to render at two sizes for windows that stradle
monitors, and it is very hard to reliably and race-freely track what
output your window is and dynamically resize the geometry as it moves
around. Not to mention the many display-global options X has, such as
mouse acceleration, pointer size, etc, that would be wrong in a hidpi
multi-monitor situation.

I wouldn't say it is impossible to fix this by introducing X extensions
as needed, but this will be a major amount of work.