Check behavior of widgets with display scaling on Linux and Windows

[t20100]

Make sure there is no major issues when "fractional scale" is applied to the display by the OS: for PySide6 & PyQt6, with matplotllib & OpenGL plots, also check silx view.

Related to silx-kit/pymca#1182 (comment)

[sergey-yaroslavtsev]

Matplotlib fonts under Windows scale could be fixed with:

if sys.platform == 'win32':
        os.environ["QT_ENABLE_HIGHDPI_SCALING"] = "0"

Everything else will still be scaled.

To avoid any effect from Windows scaler:

    if sys.platform == 'win32':
        os.environ["QT_ENABLE_HIGHDPI_SCALING"] = "0"
        os.environ["QT_SCALE_FACTOR"] = "1"
        os.environ["QT_AUTO_SCREEN_SCALE_FACTOR"] = "0"
        os.environ["QT_FONT_DPI"] = "96"

96 is not an absolute value - will work on any actual screen DPI - it is just what windows assumes as 100%.
Do not know if such approach could lead to any bug...

[t20100]

From what I can test, I didn't found major issue with silx view and screen scaling.
Rendering is not perfect but I would not expect perfect rendering from fractional scaling.

With matplotlib backend:

Normal dpi screen (~90dpi):

• 100% scaling: Vertical label not so nice
  
• 125% scaling: Vertical label not so nice & aliased plot border
  
• 150% scaling
  

Higher dpi screen (~160dpi):

• 100% scaling: Vertical label not so nice
  
• 125% scaling: aliased plot border
  
• 150% scaling
  

[t20100]

OpenGL backend text size does not change when screen scaling change while it changes with the matplotlib backend.

[sergey-yaroslavtsev]

150% scale on Windows:

silx view --fresh test.h5

silx view --use-opengl-plot test.h5

As for

silx view test.h5

it depends if it is done after fresh (or on start) or after opengl - it repeat the previous behavior. I think it is matplotlib issue.

[t20100]

On the computer I am testing, the difference I see comes from a difference of behavior:

• OpenGL backend keeps a constant font size no matter of the display scale.
• matplotlib backend enlarges the font according to the display scale.

As for the labels that goes outside of plot are, we should switch to matplotlib tight layout: #4488

Do we want to provide the same behavior for the OpenGL backend as for matplotlib? or the other way around?

For me this can wait for next release, comment if this is more important.

[t20100]

Tested with silx 3.0.0rc2 with up-to-date dependencies and pyside6: behaves fine.