3 ms·

If your UI is fast enough, why not in complex UI’s either? I’d say it gives you good motivation to keep your UI handling code as fast as possible.

• mort96 1y ago
  Doesn't egui always re-render? I like my idle apps to be doing nothing, I don't want them running their render loop in the background
  • baq 1y ago
    do you run without a compositor? I get where you're coming from, but 'idle' can mean a lot of different things and redrawing the whole UI at 60hz is not necessarily 'not idle' nowadays.
    • mort96 1y ago
      I run with a compositor, which is exactly why it's so great for the application to just draw its window once and then the compositor has the window's contents as a texture. The compositor can do whatever it wants with that texture without involvement from the application.
  • user____name 1y ago
    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).
  • freefrog1234 1y ago
    By default it re-renders on each event. This isn't often on mobile apps, but moving a mouse across a desktop app triggers multiple vents. There is a function call to request a re-render if you want not to wait for an event.
    • mort96 1y ago
      So if it's just an idle visible application, does it not render at all because there are no events? Or am I right that there's some idle redrawing going on
      • Philpax 1y ago
        With eframe, it does not re-render when idle, no. You need to have another thread that forces it to redraw on your own schedule. It will also redraw when an event occurs (mouse movement, keyboard presses, interacting with the application in general.)
  • the__alchemist 1y ago
    I think the default behavior is to only re-render if the window is active/focused. You can trigger a render at specific points, including in the main loop, which will result in the behavior you mention. This can be problematic, e.g. some of the sensor interfaces I have, I want to always display correct data, even if not focused. So, I have to decide if I want to have old data shown in the background misleading users, or have a per penalty from constant renders. Or try something else to be clever. (Maybe have it update at a low rate if not focused? I think that's the move...)
    • andsoitis 1y ago
      > You can trigger a render at specific points, including in the main loop, which will result in the behavior you mention. sounds analogous to manual memory management
      • hoppp 1y ago
        Which is completely fine. There are bugs but unlike with memory management, render bugs are more in your face.
        • andsoitis 1y ago
          which is why, I think, it is better to not have to do that manual rendering gymnastics when retained mode does it for you.
          • mort96 1y ago
            Let's not pretend that retained mode is somehow easy. Procedurally changing the system's state in response to events gets pretty complex. A philosophy which approximates the II as a function of state is tempting, in a lot of ways. As someone with a fair amount of experience of both retained mode and immediate mode UIs, I can't confidently say that retained mode requires less "mental gymnastics" than immediate mode.
      • mort96 1y ago
  • WhyNotHugo 1y ago
    I suspect (and hope) you can block the main loop if no events are received. This avoids re-rendering if the UI is not visible and no interaction has happened.
  • throwawayffffas 1y ago
    You typically set it up so that it does not re-render when it's idle. Or at least not at 60fps. By the way once upon a time, visual studio code I think it was, was using like 20% cpu when idle just because of the blinking cursor, fun.