Re: HiDPI and fractional scaling

[Loïc Minier <loic minier dooz org>]

On Mon, Feb 03, 2014, Alexander Larsson wrote:
> 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.

Ah I see why you meant multi-monitor issues with X.  I'm indeed not sure
it's worth adding extensions to fix these, perhaps in a mixed stack e.g.
Wayland/X we can just keep X apps on one screen or the other, but not
allow rendering a window on two monitors at the same time.

I recently heard GNOME stack was assuming a hardcoded 96dpi.  Is this
still true and is this multi-monitors issue the only reason it does?

It seems to me X can properly expose the DPI, physical dimensions and
logical dimensions in pixels of each screen, so would it be possible to
use these correctly wherever the app starts, and signal the app if it
ever needs to move (as a whole) to a different output?

-- 
Loïc Minier