Cache bounding boxes for "senses"

[akhilman]

We can save the bounding boxes of widgets during rendering in lists (or maybe a binary tree) for each sense type. So in the next frame, we could cheaply check if the GUI will respond to user input and skip all rendering if not needed.

[emilk]

This is a pretty neat idea for saving some CPU in the "reactive" mode for when the egui is not covering the entire screen (e.g. in a game).

[Raj2032]

Has this feature been implemented yet?

[akhilman]

I think It could work also with a full screen UI. We may skip the mouse events when the cursor travels over the widgets that have not sense for "mouse over".

[akhilman]

The idea is to reduce the number of redraws in reactive mode.

Right now, in reactive mode, the egui redraws window on every event. For example, when the mouse cursor moves over the window, each frame is redrawn, regardless of whether there will be any reaction to the mouse move event. I suggest using bounding boxes and event sensing flags to filter events so that redrawing occurs only when the widget actually responds to the event. So if the widget under the cursor senses the "mouse hover" event, then we need only two events, when the mouse enters the widget's borders and when it leaves them.

Redrawing only changed widgets will require caching and invalidating the cache, I'm not sure if this is easily achievable in immediate mode.

[mankinskin]

Got it.. sounds like a good idea. Asynchronous calls could just call request_repaint to show their changes.

Yeah, something like a cache for the last frame would definitely be helpful for a lot of things. And it shouldn't be too hard to do, I'd think.. basically just store all of the Responses after each frame?

[Raj2032]

@akhilman Are you planning to implement such a feature or do I have to use "bounding boxes"?

[akhilman]

@akhilman Are you planning to implement such a feature or do I have to use "bounding boxes"?

Not yet. I'm waiting for more details on #843 that might help me.
If you want to implement this feature yourself, you are welcome.

[Raj2032]

@akhilman Truth be told I never used this GUI library at all, I am considering using it. I might use it for a project (I can then become more familiar with it) and then I can help out.

I was looking at lru-rs https://crates.io/crates/lru which caches things, I don't know if this would help or not.

[akhilman]

Implementation could be shared with #1250.

[Raj2032]

Is this similar to retained mode?

[akhilman]

Not really. We are still drawing everything every frame, but this cache will help us to skip some frames triggered by mouse events.

[Raj2032]

AH right mate