RE: [fltk.coredev] Windows and Linux scale_factor (hiDPI) trouble - [General Use]

[MacArthur, Ian (Leonardo, UK)]

> My problem is that Linux reports a scale factor of 2.0, when it should
> be reporting a screen scale of 1.25.
> I solved the issue with Windows, but Linux reports an incorrect screen_scale.

> > What do you mean exactly by "Linux reports a scale factor of 2.0" ?
> > The scale factor known to FLTK is visible with the test program test/fullscreen.

> And indeed it does.  When I set the Desktop preferences to 125% (or any other setting other than 100%), I get:
> Screen 0: 1536x864@0,0 DPI:95.6x94.6 scale:2.00
> To set the scaling factor for my screen I am RMB on the Desktop->Display (or is it Screen) Configuration
> and setting Scale to a different value (and Apply).


I seem to remember that there was an issue with X11 servers, or maybe it was some WM's, only handling integer scale factors, at least at some point, so it is possible that it really is 2, I guess?



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[Albrecht Schlosser]

On 8/6/20 1:42 PM MacArthur, Ian (Leonardo, UK) wrote:
[Gonzalo wrote:]

>> And indeed it does.  When I set the Desktop preferences to 125% (or any other setting other than 100%), I get:
>> Screen 0: 1536x864@0,0 DPI:95.6x94.6 scale:2.00
>> To set the scaling factor for my screen I am RMB on the Desktop->Display (or is it Screen) Configuration
>> and setting Scale to a different value (and Apply).
>
> I seem to remember that there was an issue with X11 servers, or maybe it was some WM's, only handling integer scale factors, at least at some point, so it is possible that it really is 2, I guess?

I can't remember for sure and couldn't find it, but I believe that
Gonzalo mentioned Ubuntu.

Reading the following article which is about Linux Mint but mentions
Ubuntu which Mint is based on, I get the impression that Ubuntu doesn't
support other scaling factors than 1.0 and 2.0:

https://www.omgubuntu.co.uk/2020/02/cinnamon-desktop-fractional-scaling-support

Citation, regarding Linux Mint 20:

“By being able to set the scaling for each monitor independently and
allow for scaling values of not only 100% and 200% but also 125%, 150%,
175%, we’re hoping to get higher pixel density and allow HiDPI and
non-HiDPI monitors to play well with each others.”

... and further:

"If Mint can stick the landing of this feature then the Cinnamon desktop
and Linux Mint, which uses Cinnamon by default, will gain a major
selling point over regular Ubuntu."

See the last cited sentence.

Well, that could also mean that you'd get it on Ubuntu as well if you
used the Cinnamon desktop.

[gga]

On 6/8/20 09:05, Albrecht Schlosser wrote:
>
> I can't remember for sure and couldn't find it, but I believe that
> Gonzalo mentioned Ubuntu.
>

Yes, I am on Ubuntu.

> Reading the following article which is about Linux Mint but mentions
> Ubuntu which Mint is based on, I get the impression that Ubuntu
> doesn't support other scaling factors than 1.0 and 2.0:
>
> https://www.omgubuntu.co.uk/2020/02/cinnamon-desktop-fractional-scaling-support
>
>
> Citation, regarding Linux Mint 20:
>
> “By being able to set the scaling for each monitor independently and
> allow for scaling values of not only 100% and 200% but also 125%,
> 150%, 175%, we’re hoping to get higher pixel density and allow HiDPI
> and non-HiDPI monitors to play well with each others.”
>

Well, the option to set at least one monitor at 125, 150 and 175% is
there in Gnome and it works.

> ... and further:
>
> "If Mint can stick the landing of this feature then the Cinnamon
> desktop and Linux Mint, which uses Cinnamon by default, will gain a
> major selling point over regular Ubuntu."
>
> See the last cited sentence.
>
> Well, that could also mean that you'd get it on Ubuntu as well if you
> used the Cinnamon desktop.
>

I tried Cinnamon and it gave me only two choices for my monitor: Normal
and hiDPI.  No percentages at all :(  I guess I don't have the latest
cinnamon yet.

--
Gonzalo Garramuño

[Albrecht Schlosser]

Citing the article (date: Feb 2020):
"Cinnamon 4.6 is expected to introduce support for fractional scaling
when it’s released later this year..."

So it ought to be at least 4.6 *if* it was introduced in that version as
expected by the author.

[Manolo]

The scale factor FLTK uses under Linux is the value of the Xft.dpi X resource

divided by 96.

That value can be read by command

    xrdb -query

The FLTK scale factor can be further changed typing ctrl-+, or using

the FLTK_SCALING_FACTOR  environment variable. This is all described at:

   https://fltk.gitlab.io/fltk/drawing.html#ssect_DrawingUnit

Under Ubuntu, the settings application, Displays item, allows to set the scale

to 100% or 200%. Setting it to 200% gives Xft.dpi the value 192 and the value 2 to the

FLTK scaling factor (test/fullscreen shows this value).

Recently an option called "Fractional scaling" appeared

allowing to set it to 125%, 150% etc. Under Virtualbox I use, that's not usable

so I don't known how it works.

To get fractional scale values, another app called "Tweaks" is useful.

Its "Fonts" item contains a "Scaling factor" value that can be set at will

to fractional values (e.g. 1.27) and that in fact controls Xft.dpi,

which FLTK follows, as written above.

What is the meaning of

    "I solved the issue with Windows, but Linux reports an incorrect screen_scale." ?

Does the GL window draw correctly under Linux also?

[gga]

On 6/8/20 14:03, Manolo wrote:
>     "I solved the issue with Windows, but Linux reports an incorrect
> screen_scale." ?
> Does the GL window draw correctly under Linux also?

Yes, the GL window draws correctly.  If I use the Tweaks utility it does.

--
Gonzalo Garramuño