Proposal: global user UI scaling factor for desktop apps

[elhijamuhammed]

I’m building a desktop app using Slint and noticed a usability issue related to Windows display/text scaling.
A user running high display scaling ended up with parts of the UI cropped or inaccessible because many desktop apps use fixed px-based layouts.

I was thinking about a global user UI scaling factor that could multiply layout sizes consistently across the application.
For example:
effective_size = original_size * user_scale_factor
So if a user or application sets:
user_scale_factor = 0.8
then:

• 40px button -> 32px
• 16px font -> 12.8px
• spacing/padding/radius/etc also scale

This could help applications compensate for accessibility scaling or provide app-level zoom similar to browsers/editors.
Possible APIs could be something like:
window.set_user_scale_factor(0.8)
or
user-scale-factor: 0.8;
I know this may interact with existing DPI/platform scaling internally, but I wanted to ask whether something like this would fit Slint’s architecture or roadmap.

[ogoffart]

There is already the SLINT_SCALE_FACTOR env variable. https://docs.slint.dev/latest/docs/slint/guide/development/debugging_techniques/#user-interface-scaling.

Otherwise this may also be relevant: #4418