slint-borderless-windows

A Rust library that provides a native-feeling borderless window with a custom titlebar for Slint applications on Windows.

Features

• Removes the default OS window frame (no-frame: true) while preserving native behavior
• Windows 11 DWM drop shadow and rounded corners via DwmExtendFrameIntoClientArea and DwmSetWindowAttribute
• Edge and corner resize hit-testing via a WinAPI window subclass (WM_NCHITTEST)
• Ready-to-use Titlebar Slint component with minimize, maximize/restore, and close buttons
• Drag-to-move via winit's drag_window()
• Double-click titlebar to toggle maximize/restore

Requirements

• Windows (the DWM and subclass APIs are Windows-only)
• Rust edition 2024
• Slint 1.16.1+

Usage

1. Add the dependency

In your Cargo.toml:

[dependencies]
slint_borderless_windows = { git = "https://github.com/Drew-Chase/slint_borderless_windows.git" }
slint = { version = "1.16.1", features = ["backend-winit"] }

2. Import the Titlebar component in your .slint file

import { Titlebar, WindowControls } from "path/to/titlebar.slint";

// Re-export WindowControls so it is accessible from Rust
export { WindowControls }

export component MainWindow inherits Window {
    no-frame: true;

    VerticalLayout {
        padding: 0px;
        spacing: 0px;

        Titlebar {
            title: "My App";
        }

        // Your content here
    }
}

Setting no-frame: true on the root Window removes the OS chrome. The Titlebar component replaces it.

3. Wire up the callbacks in Rust

use slint_borderless_windows::TitlebarSetup;

slint::include_modules!();

fn main() -> Result<(), slint::PlatformError> {
    let app = MainWindow::new().expect("Failed to create main window");

    let frame = app.as_weak().setup_borderless().expect("Failed to setup custom frame");
    let frame_maximize = frame.clone();
    let frame_close = frame.clone();
    let frame_drag = frame.clone();
    let frame_dblclick = frame.clone();

    app.global::<WindowControls>().on_maximize(move || frame_maximize.toggle_maximized());
    app.global::<WindowControls>().on_close(move || frame_close.close());
    app.global::<WindowControls>().on_drag(move || frame_drag.drag());
    app.global::<WindowControls>().on_double_click(move || frame_dblclick.toggle_maximized());
    app.global::<WindowControls>().on_minimize(move || frame.minimize());

    app.run()?;
    Ok(())
}

setup_borderless() applies the DWM styling and installs the resize subclass. It returns a WindowFrame handle that exposes the window control methods.

API

TitlebarSetup trait

Implemented on slint::Weak<T>. Call setup_borderless() after creating your component to apply the custom frame.

fn setup_borderless(&self) -> Result<WindowFrame<T>, slint::PlatformError>

WindowFrame<T>

A lightweight, cloneable handle (backed by slint::Weak<T>) for controlling the window.

Titlebar component (titlebar.slint)

A 32px tall titlebar strip. Drop it at the top of a VerticalLayout.

WindowControls global (titlebar.slint)

Bridges the Slint UI to Rust. Wire up each callback from Rust as shown above.

How it works

setup_borderless() performs three things on the underlying Win32 window handle:

1. Rounded corners — calls DwmSetWindowAttribute with DWMWCP_ROUND
2. Drop shadow — calls DwmExtendFrameIntoClientArea with a 1px bottom margin, which is enough for DWM to render a shadow without exposing any native frame
3. Resize hit-testing — installs a window subclass via SetWindowSubclass that intercepts WM_NCHITTEST and returns the correct HT* values for all eight resize edges and corners

WM_NCCALCSIZE is also intercepted and returns 0 when wParam != 0, which tells Windows the entire window rect is client area — removing all non-client chrome.

Example

A full working example is in examples/basic_example/. Build and run it with:

cd examples/basic_example
cargo run