Avoid redundant redraw requests in native run loop

[rustbasic]

Avoid redundant redraw requests in native run loop

• Related 100% CPU usage since the update to wgpu 0.20 #5092
• Related pure_glow high CPU usage #7401
• Related Solution (#8314): Drag-resize causes application lock-up #8318
• Related Reactive eframe application uses 100% of one core on mouse move #8326

Summary

Avoid repeatedly requesting redraws for the same native window while a previous
request_redraw() is still pending.

Details

request_redraw() schedules a future WindowEvent::RedrawRequested. In reactive
apps, repeatedly calling request_redraw() before that event is delivered can
keep the event loop unnecessarily busy.

This PR adds per-window pending redraw tracking:

• mark a window as pending when request_redraw() is called
• skip additional redraw requests while pending
• clear the pending state on WindowEvent::RedrawRequested
• clear it for invisible/minimized windows that are painted directly

The run loop now also falls back to ControlFlow::Wait when there is no next
scheduled repaint, instead of relying on ControlFlow::Poll.

This should reduce redundant redraw requests and unnecessary CPU usage in
reactive native applications.

[github-actions]

Preview available at https://egui-pr-preview.github.io/pr/8341-p107
Note that it might take a couple seconds for the update to show up after the preview_build workflow has completed.

View snapshot changes at kitdiff

[rustbasic]

The fact that the deferred viewport fails to redraw when the ROOT viewport is clicked is an existing bug and is unrelated to this PR.

Solved :

• Fix: deferred viewport does not redraw when clicking ROOT viewport (Windows) #8395