4 ms·

Any quarter decent imgui implementation will idle when there's no input or active animations, and the renderer can generate dirty tiles or rects to unnecessary

Any quarter decent imgui implementation will idle when there's no input or active animations, and the renderer can generate dirty tiles or rects to unnecessary redrawing -- if it matters, gpus are ridiculously overpowered for drawing a bunch of rectangles. Ui logic is usually firmly in the microseconds realm.

mort96 1y ago
I agree that this is not a necessary downside to immediate mode GUIs, but we're talking about egui specifically here. AFAIK, egui always redraws at some relatively high rate even when nothing is happening. (I'm having trouble finding documentation about what that rate is though.)
- Boxxed 1y ago
  That's not true, it only re-renders if there's an input event or an animation running. This is very easy to see if you just put a `println!` in your UI logic. This is also mentioned in the gui docs here https://github.com/emilk/egui#why-immediate-mode https://github.com/emilk/egui#why-immediate-mode: > egui only repaints when there is interaction (e.g. mouse movement) or an animation, so if your app is idle, no CPU is wasted.
  - amelius 1y ago
    Iiuc, a tiny clock in the top right corner of the screen will trigger O(n) work where n is the number of elements on the entire screen. On every change of the clock, e.g. every second. This may be more if there are smooth animations, e.g. 25 times per second if that is the animation frame rate.
    - Aeolun 1y ago
      Sure, but it will consume less CPU than an idle instance of Electron. Or the effort it takes to redraw a React app even once.
- ModernMech 1y ago
  There are two modes, reactive and continuous. You can switch between them here in the backend tab: https://www.egui.rs/ https://www.egui.rs/ Reactive mode is the one you are looking for.
pixelpoet 1y ago
I really wish this were built into imgui as a first-class use case instead of requiring a hodgepodge mix of unofficial hacks. I recall the author posting an imgui update saying this will be an officially supported mode, but AFAIK it's still not the case. Otherwise I would be building all my applications with imgui going forward. Re-rendering the screen, even if it's fast, incurs a lot of memory bandwidth to draw everything and swap framebuffers etc. Not something you'd like to happen on mobile, in particular. Just because the waste is "small", doesn't mean it's acceptable.
- halfcat 1y ago
  Does ImGui work on mobile? I’ve seen it run in web assembly on mobile but typically none of the keyboard inputs work (the mobile keyboard doesn’t pop up, so effectively it’s not usable, at least in that approach).

mort96 1y ago

I agree that this is not a necessary downside to immediate mode GUIs, but we're talking about egui specifically here. AFAIK, egui always redraws at some relatively high rate even when nothing is happening. (I'm having trouble finding documentation about what that rate is though.)

Boxxed 1y ago
That's not true, it only re-renders if there's an input event or an animation running. This is very easy to see if you just put a `println!` in your UI logic. This is also mentioned in the gui docs here https://github.com/emilk/egui#why-immediate-mode https://github.com/emilk/egui#why-immediate-mode: > egui only repaints when there is interaction (e.g. mouse movement) or an animation, so if your app is idle, no CPU is wasted.
- amelius 1y ago
  Iiuc, a tiny clock in the top right corner of the screen will trigger O(n) work where n is the number of elements on the entire screen. On every change of the clock, e.g. every second. This may be more if there are smooth animations, e.g. 25 times per second if that is the animation frame rate.
  - Aeolun 1y ago
    Sure, but it will consume less CPU than an idle instance of Electron. Or the effort it takes to redraw a React app even once.
ModernMech 1y ago
There are two modes, reactive and continuous. You can switch between them here in the backend tab: https://www.egui.rs/ https://www.egui.rs/ Reactive mode is the one you are looking for.

pixelpoet 1y ago

I really wish this were built into imgui as a first-class use case instead of requiring a hodgepodge mix of unofficial hacks. I recall the author posting an imgui update saying this will be an officially supported mode, but AFAIK it's still not the case. Otherwise I would be building all my applications with imgui going forward. Re-rendering the screen, even if it's fast, incurs a lot of memory bandwidth to draw everything and swap framebuffers etc. Not something you'd like to happen on mobile, in particular. Just because the waste is "small", doesn't mean it's acceptable.

halfcat 1y ago
Does ImGui work on mobile? I’ve seen it run in web assembly on mobile but typically none of the keyboard inputs work (the mobile keyboard doesn’t pop up, so effectively it’s not usable, at least in that approach).