Automatically set initial window size to fit contents

[archer884]

Here's what I got:

It's not bad, and I like that it wasn't that hard to create, but there's a problem: that extra space at the bottom is driving me crazy, and it changes size on different screens and operating systems and so forth. In fact, on some systems, this overflows. I would love to figure out some way to set the window's initial size based on what's IN the window rather than just setting it by trial and error in a run/edit loop, you know? But I haven't figured out a working way to do that.

This is less of a problem horizontally because I can trust the width of these elements to scale to a degree, but I'll admit that I have a similar problem with X and Y both.

Edit: I just realized that, technically, this isn't a window. It's built around CentralPanel instead. I just tried using Window, but that exhibits the same problem except that now there's a perfectly-sized Window inside the (not-so-perfectly-sized) application window, which is what I was referring to before, colloquially, as a "window."

Edit 2: It's really not essential that this be automatic. It would be fine to be able to know how much room the ui elements take up and then perform a resize by hand. I tried that at one point, actually, but the results weren't great. The size reported on the first frame is wrong; the size reported on the second frame appears to be correct, but by that time it seems to be too late to resize the window?

Edit the Third: I have now split the UI into two panels. With a footer panel at the bottom, it's definitely less obvious that there is "extra" space in the UI, and I have an element at the bottom of the central panel that can grow a little without looking too funny. This is a relatively satisfying result, albeit not completely, but I'd still like to know if there's some way to add up what the appropriate size for a given UI is. Also, yeah, if there's a smarter way to do this stuff, let me know!

[liuzhch1]

hi, have you found a better way to achieve this? I am also troubled by this problem. I searched for a long time and only found this helpful discussion.

We can use this tricky way to make the window fit its content when it starts

• First time render with egui::Window which auto shrink to content size
• Get the size of the window
• Send ViewportCommand::InnerSize command to adjust the native window size
• Then render with egui::CentralPanel to get a native window

Here is the code permalink

fn main() {
  let app = AppGUI::default();
  eframe::run_native(
    "eframe window size fit content",
    eframe::NativeOptions::default(),
    Box::new(|_cc| Ok(Box::new(app))),
  )
  .unwrap();
}


struct AppGUI {
  name: String,
  age: u8,
  content: String,
  _first_render: bool,
}


impl Default for AppGUI {
  fn default() -> Self {
    Self {
      name: "John".to_string(),
      age: 20,
      content: "This demo shows how the eframe window size fit content works.".to_string(),
      _first_render: true,
    }
  }
}
impl AppGUI {
  fn pre_render(&mut self, ctx: &eframe::egui::Context) {
    egui::Window::new("pre_render")
      .title_bar(false)
      .fixed_pos((0.0, 0.0))
      .show(ctx, |ui| {
        self.render(ui);
      });
  }
  fn render(&mut self, ui: &mut egui::Ui) {
    ui.add(
      egui::Label::new(egui::RichText::new("Hello, world!").heading())
        .wrap_mode(egui::TextWrapMode::Extend),
    );
    ui.label(format!("Name: {}", self.name));
    ui.label(format!("Age: {}", self.age));
    ui.label(format!("{} ", self.content));
  }
}


impl eframe::App for AppGUI {
  fn update(&mut self, ctx: &eframe::egui::Context, _frame: &mut eframe::Frame) {
    if self._first_render {
      self.pre_render(ctx);
      self._first_render = false;
      let window_size = ctx.used_size();
      ctx.send_viewport_cmd(egui::ViewportCommand::InnerSize(window_size));
    } else {
      egui::CentralPanel::default().show(ctx, |ui| {
        self.render(ui);
      });
    }
  }
}

Not quite elegant, hope it helps you.