Rust Windows Transparent Overlay

main.rs

[package]
name = "transparent_overlay"
version = "0.1.1"
edition = "2021"

[dependencies]
windows = { version = "0.58", features = [
    "Win32_Foundation",
    "Win32_Graphics_Gdi", 
    "Win32_UI_WindowsAndMessaging",
    "Win32_System_Com"
] }
windows-core = "0.58" 

#![windows_subsystem = "windows"]

use windows::{
    core::{Result, w, Error},
    Win32::{
        Foundation::{HWND, LRESULT, WPARAM, LPARAM, COLORREF}, 
        System::Com::{CoInitializeEx, COINIT_APARTMENTTHREADED},
        UI::WindowsAndMessaging::{
            CreateWindowExW, DefWindowProcW, GetMessageW, RegisterClassW, SetLayeredWindowAttributes,
            ShowWindow, TranslateMessage, DispatchMessageW, PostQuitMessage, MSG, WNDCLASSW,
            WS_EX_LAYERED, WS_EX_TRANSPARENT, WS_POPUP, LWA_COLORKEY, SW_SHOW, WM_DESTROY,
            WM_CLOSE, WINDOW_EX_STYLE, WINDOW_STYLE,
        },
    },
};

fn main() -> Result<()> {
    unsafe {
        CoInitializeEx(None, COINIT_APARTMENTTHREADED).ok()?;

        let class_name = w!("transparent_overlay_class");

        let wnd_class = WNDCLASSW {
            lpfnWndProc: Some(wnd_proc), 
            lpszClassName: class_name,
            ..Default::default()
        };
        
        RegisterClassW(&wnd_class);

        let hwnd = CreateWindowExW(
            WINDOW_EX_STYLE(WS_EX_LAYERED.0 | WS_EX_TRANSPARENT.0),
            class_name,
            w!("Overlay"),
            WINDOW_STYLE(WS_POPUP.0),
            100,
            100,
            500,
            400,
            None,
            None,
            None,
            None,
        );
        
        let hwnd = hwnd.ok().expect("Failed to create window");

        SetLayeredWindowAttributes(hwnd, COLORREF(0), 0, LWA_COLORKEY)
            .ok()
            .expect("Failed to set layered window attributes");

        ShowWindow(hwnd, SW_SHOW);

        let mut msg = MSG::default();
        while GetMessageW(&mut msg, None, 0, 0).into() {
            TranslateMessage(&msg);
            DispatchMessageW(&msg);
        }
    }

    Ok(())
}

extern "system" fn wnd_proc(hwnd: HWND, msg: u32, wparam: WPARAM, lparam: LPARAM) -> LRESULT {
    match msg {
        WM_CLOSE | WM_DESTROY => {
            unsafe { PostQuitMessage(0); }
            LRESULT(0)
        }
        _ => unsafe { DefWindowProcW(hwnd, msg, wparam, lparam) },
    }
}