build.rs

fn main() {
    #[cfg(windows)]
    add_windows_icon();
}

#[cfg(windows)]
fn add_windows_icon() {
    use image::{
        codecs::ico::{IcoEncoder, IcoFrame},
        ColorType,
    };

    let ico_path = "assets/logo.ico";
    if std::fs::metadata(ico_path).is_err() {
        let ico_frames = load_images();
        save_ico(&ico_frames, ico_path);
    }

    let mut res = winres::WindowsResource::new();
    res.set_icon(ico_path);
    res.compile().expect("Could not attach exe icon");

    fn load_images() -> Vec<IcoFrame<'static>> {
        let sizes = vec![32, 64, 128, 256];
        sizes
            .iter()
            .map(|s| {
                IcoFrame::as_png(
                    image::open(format!("assets/logo_{}.png", s))
                        .unwrap()
                        .as_bytes(),
                    *s,
                    *s,
                    ColorType::Rgba8,
                )
                .unwrap()
            })
            .collect()
    }

    fn save_ico(images: &[IcoFrame<'_>], ico_path: &str) {
        let file = std::fs::File::create(ico_path).unwrap();
        let encoder = IcoEncoder::new(file);
        encoder.encode_images(images).unwrap();
    }
}