assertion 'width >= -1' failed on NixOS/Sway

Author: ZachiahCreated Feb 3, 2024Updated Nov 20, 2025

When trying to run one of the examples from the book, the window is created, but no widgets render:

use druid::widget::Label;
use druid::{AppLauncher, Widget, WindowDesc};

fn build_ui() -> impl Widget<()> {
    Label::new("Hello world")
}

fn main() {
    let main_window = WindowDesc::new(build_ui())
        .window_size((600.0, 400.0))
        .title("My first Druid App");
    let initial_data = ();

    AppLauncher::with_window(main_window)
        .launch(initial_data)
        .expect("Failed to launch application");
}

In the console I get this error:

(rust-plugin-try:190043): Gtk-CRITICAL **: 16:10:25.770: gtk_window_set_default_size: assertion 'width >= -1' failed

I apologize if this isn't the right place to put this issue, but I haven't had any issues running apps so far so It seems to be specific to this project? I'm willing to provide any version numbers/environment variables asked of me, but here are some basics:

Rust: 1.75.0 Druid: 0.8.3 Sway: 1.8.1 Nix: 2.18.1 Neofetch (logo removed):

zachiahsawyer@nixos
-------------------
OS: NixOS 23.11.2413.32f63574c85f (Tapir) x86_64
Host: LENOVO LNVNB161216
Kernel: 6.6.8
Uptime: 20 hours, 25 mins
Packages: 763 (nix-system), 1008 (nix-user)
Shell: zsh 5.9
Resolution: 3072x1920
WM: sway
Theme: Catppuccin-Macchiato-Compact-Pink-Dark [GTK2/3]
Terminal: alacritty
CPU: AMD Ryzen 7 6800HS Creator Edition (16) @ 4.785GHz
GPU: AMD ATI Radeon 680M
GPU: NVIDIA GeForce RTX 3050 Mobile
Memory: 11912MiB / 13669MiB

Also, I don't know how relevant it is, but I'm using a shell.nix file to setup the environment

which looks like this:

{ pkgs ? import <nixpkgs> {} }:

pkgs.mkShell {
    buildInputs = [
        pkgs.alsaLib
        pkgs.pkg-config
        pkgs.pango
        pkgs.cairo
        pkgs.gdk-pixbuf
        pkgs.gtk3
    ];
    shellHook = ''
        export PKG_CONFIG_PATH=${pkgs.alsaLib}/lib/pkgconfig:${pkgs.pango}/lib/pkgconfig:${pkgs.cairo}/lib/pkgconfig:${pkgs.gdk-pixbuf}/lib/pkgconfig:${pkgs.gtk3}/lib/pkgconfig:$PKG_CONFIG_PATH
    '';
}

Source: linebender/druid

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