<AWT Dev> Why no fractional scale factor in AWT with X11?

Phil Race philip.race at oracle.com
Wed Nov 6 19:27:14 UTC 2019

Fractional is not as easy as you make out.
There is lots of potential for rendering artifacts and unfortunate rounding.

Contrary to what you state, macos is 2x only so this isn't unique.
Never mind if it is stored in a float/double. Retina is 2X.
Also macos was easier because text scales linearly in the apple model of 
text rendering.

So it was safer and somewhat easier to make it integer on Linux.

On Windows however fractional scales are common so it was a must there,
and there are still occasional bugs as a consequence.


On 11/6/19 11:02 AM, Florent Lioult wrote:
> Hi,
> Contrary to Windows and MacOS X, the X11 implementation of AWT on 
> Linux doesn't use a floating scale factor internally. For instance, 
> setting the Gnome desktop property 
> 'org.gnome.desktop.interface/text-scaling-factor' to 2.2 will produce 
> a x2.0 transform for a Swing application.
> I've had a look into the latest JDK sources (14) and the coercion to 
> int seems arbitrary to me considering that both the portable layer and 
> the native side rely on doubles. In fact, I've removed it without much 
> changes and everything seems to work fine. Honestly, I haven't 
> conducted enough tests to claim it hasn't any issues, but I didn't see 
> blatant problems neither. Of course, there are a lot of resources on 
> the net discussing HiDPI support with Java on various platforms and I 
> understand that the scale factor could be rounded for aesthetic 
> reasons, but I'm not sure it's the rational behind how the code 
> behaves today for X11.
> Is there a specific reason I ignore or is this capability just 
> something nobody is interested in on Linux?
> - Florent

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