Reactive Rendering #2662
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Reactive Rendering #2662
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hecrj
added
feature
... and fix the redraw queue logic in `iced_winit`.
If we do not request it, macOS does not get any `RedrawRequested` events. Shouldn't `winit` [take care of this]? Probably a bug. [take care of this]: https://docs.rs/winit/0.30.5/winit/event/enum.WindowEvent.html#variant.RedrawRequested
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This PR changes the runtime to only perform a redraw of the user interface when either an
updateoccurs, or a widget explicitly requests it.Currently,
icedrenders all the time unconditionally on every runtime event. Effectively, this means that when you move your mouse around in anicedapplication, the runtime can easily draw hundreds of identical frames—wasting plenty of resources.The changes here make both the runtime and the built-in widgets aware of their last status when drawn, and only request a redraw when needed. This should normally translate to a lower CPU and (specially) GPU usage when interacting with most applications.
As a consequence, the
WidgetandOverlaycontract now require implementors to explicitly request redraws when necessary. Most of the time, this entails some kind of "diffing" during event processing to figure out if the widget state has changed.This new feature is enabled by default but, since it makes widget implementation more difficult and may not make sense for highly dynamic applications, a user can opt out by enabling the
unconditional-renderingfeature; which restores the old behavior.Related important breaking changes include:
Widget::on_eventdoes not return anevent::Statusanymore. Instead, a widget can capture an event by callingShell::capture_event. Since widget logic is generally quite imperative, this paradigm fits better and is also more consistent with other shell-related logic.Widget::on_eventhas been renamed toupdate.Programboth forcanvasandshadernow return awidget::Action, which can be leveraged to either publish a message or request a redraw, and also event capturing.Eventtypes forcanvasandshaderhave been removed. They now simply use the foundationalcore::Eventtype.