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.

Method	Description
minimize()	Minimizes the window
maximize(bool)	Sets maximized state explicitly
toggle_maximized()	Toggles between maximized and restored
close()	Quits the Slint event loop
drag()	Initiates a native window drag-move

Titlebar component (titlebar.slint)

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

Property	Type	Default	Description
title	string	"Application"	Text displayed in the titlebar
icon	image	(none)	Optional icon shown left of the title

WindowControls global (titlebar.slint)

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

Callback	Triggered by
minimize()	Minimize button click
maximize()	Maximize/restore button click
close()	Close button click
drag()	Mouse-down on the titlebar drag area
double-click()	Double-click on the titlebar drag area

Property	Type	Description
maximized	bool	Controls which icon the maximize button shows (square vs. restore). Set this from Rust when the window state changes.

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