You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.rs
    path of file: ./repos/egui/examples/screenshot/src
    
    the code of the file until where you have to start completion: #![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release

use std::sync::Arc;

use eframe::egui::{self, ColorImage};

fn main() -> Result<(), eframe::Error> {
    env_logger::init(); // Log to stderr (if you run with `RUST_LOG=debug`).
    let options = eframe::NativeOptions {
        renderer: eframe::Renderer::Wgpu,
        ..Default::default()
    };
    eframe::run_native(
        "Take screenshots and display with eframe/egui",
        options,
        Box::new(|_cc| Box::<MyApp>::default()),
    )
}

#[derive(Default)]
struct MyApp {
    continuously_take_screenshots: bool,
    texture: Option<egui::TextureHandle>,
    screenshot: Option<Arc<ColorImage>>,
    save_to_file: bool,
}

impl eframe::App for MyApp {
    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
        egui::CentralPanel::default().show(ctx, |ui| {
            if let Some(screenshot) = self.screenshot.take() {
                self.texture = Some(ui.ctx().load_texture(
                    "screenshot",
                    screenshot,
                    Default::default(),
                ));
            }

            ui.horizontal(|ui| {
                ui.checkbox(
                    &mut self.continuously_take_screenshots,
                    "continuously take screenshots",
                );

                if ui.button("save to 'top_left.png'").clicked() {
                    self.save_to_file = true;
                    ctx.send_viewport_cmd(egui::ViewportCommand::Screenshot);
                }

                ui.with
    
    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
        egui::CentralPanel::default().show(ctx, |ui| {
            if let Some(screenshot) = self.screenshot.take() {
                self.texture = Some(ui.ctx().load_texture(
                    "screenshot",
                    screenshot,
                    Default::default(),
                ));
            }

            ui.horizontal(|ui| {
                ui.checkbox(
                    &mut self.continuously_take_screenshots,
                    "continuously take screenshots",
                );

                if ui.button("save to 'top_left.png'").clicked() {
                    self.save_to_file = true;
                    ctx.send_viewport_cmd(egui::ViewportCommand::Screenshot);
                }

                ui.with_layout(egui::Layout::top_down(egui::Align::RIGHT), |ui| {
                    if self.continuously_take_screenshots {
                        if ui
                            .add(egui::Label::new("hover me!").sense(egui::Sense::hover()))
                            .hovered()
                        {
                            ctx.set_visuals(egui::Visuals::dark());
                        } else {
                            ctx.set_visuals(egui::Visuals::light());
                        };
                        ctx.send_viewport_cmd(egui::ViewportCommand::Screenshot);
                    } else if ui.button("take screenshot!").clicked() {
                        ctx.send_viewport_cmd(egui::ViewportCommand::Screenshot);
                    }
                });
            });

            if let Some(texture) = self.texture.as_ref() {
                ui.image((texture.id(), ui.available_size()));
            } else {
                ui.spinner();
            }

            // Check for returned screenshot:
            ui.input(|i| {
                for event in &i.raw.events {
                    if let egui::Event::Screenshot { image, .. } = event {
                        if self.save_to_file {
                            let pixels_per_point = i.pixels_per_point();
                            let region = egui::Rect::from_two_pos(
                                egui::Pos2::ZERO,
                                egui::Pos2 { x: 100., y: 100. },
                            );
                            let top_left_corner = image.region(&region, Some(pixels_per_point));
                            image::save_buffer(
                                "top_left.png",
                                top_left_corner.as_raw(),
                                top_left_corner.width() as u32,
                                top_left_corner.height() as u32,
                                image::ColorType::Rgba8,
                            )
                            .unwrap();
                            self.save_to_file = false;
                        }
                        self.screenshot = Some(image.clone());
                    }
                }
            });

            ctx.request_repaint();
        });
    }