Function register_texture_source 

pub fn register_texture_source(
    source: impl FnMut() -> Option<SourceFrame> + Send + 'static,
) -> TextureRegistration

Registers source as a scene texture, polled once per engine frame for its newest frame (see the module docs), and returns the registration that names it and keeps it alive.

source runs on the render thread with the frame’s external-pass drain in progress: it should only hand over a frame it already has (take from a mailbox), never block for one. A source — or an importer — that panics is retired like any panicking external pass, and the frame in flight is not leaked: a SourceFrame (like the plugin substrate’s twin) dropped while still holding its release callback runs it during the unwind.