Offscreen rendering

[vladimmi]

It was asked here and in issues before but mostly tied to some specific conditions (platform/API/etc) and some answers seem outdated.

Is there currently a way to render Slint window (or single component, if it's not tied to window) to offscreen texture/buffer? Especially having both normal and offscreen windows in a single application at the same time. Something like OffscreenWindow instead of Window to inherit or some property to make it render hidden?

If yes - is there any up-to-date example or hint where to dig? I've seen #704 saying "theoretically possible" more than a year ago but got lost looking further. Maybe something changed to this moment?

If no - is such feature tracked somewhere to follow? #7231 says "I think this is something that we want to be able to support" but I didn't found anything else on this topic.

[ogoffart]

Could you elaborate on your usecase?

The typical way to do offscreen would be to use a custom Platform implementation. This is what our testing backend does, or what we do for screenshot tests.
See https://github.com/slint-ui/slint/blob/master/tools/docsnapper/headless.rs for the tool that renders the documentation snippet into a screenshot.

But since you seem to want both a real and a off screen, that maight not be the best solution.
Another one is to use the Window::set_rendering_notifier and call Window::take_snapshot from there

[vladimmi]

Sure, I have such thing made in Qt/QML but looking for alternative approaches and Slint as markup language looks very promising.

The idea is to have an application that gathers and processes some realtime data (like a live telemetry from a racing sim, comments from a Twitch chat, etc). This data is then somehow rendered by configurable "widgets" (including user-provided slint files via interpreter, I guess) - either as usual windows or as offscreen textures to be used some other way (passed to OBS, for example, or maybe sent via network).

take_snapshot would probably be enough but doesn't that mean there should be a real visible window on screen to capture it?