Conrod is a super-young, “immediate-mode”, graphical user interface library written entirely in Rust! Before I bore you with the details, here’s a demonstration of it in action.

click click clickity click…

The Rust Story

About two or three months ago I landed on the home page after following a well-hyped HN link. Just so you know, I’m currently in the middle of developing a large real-time interactive generative music system and there’s no way in the world I’d have time to go around willy-nilly checking out new programming languages! No. Way. But then I read the headline…

“Rust is a systems programming language that runs blazingly fast, prevents almost all crashes*, and eliminates data races.”

So here I am about two or three months later - 95% through porting all of my slave-laboured C++ code to Rust, and it remains one of the best decisions I can remember making! (it should be noted that none of my laundry has been eaten… yet).

The Conrod GUI

Conrod itself is only about two weeks old, so go easy! It still requires lots of refinement and optimisation, however I think it’s showing a good amount of promise. This is also the first time I’ve had a go at “immediate-mode” UI - to be honest when I first heard of the idea I thought it sounded quite rubbish…

“How on earth would you store complex widget state without having any objects!?”


“Surely it would have to be so slow, having to create the widget every frame!?”.

Only after I started to have a play with the idea did I realise how well the “immediate-mode” approach is suited to Rust’s functional-esque style! The algebraic data types turned out to be perfect for both caching the necessary widget state and creating diverse yet concise draw signatures. Performance hasn’t yet been an issue, and I no longer see any good reason why it should be!

API Code

This is what drawing a Button looks like at the moment.

// Inside our render loop...

button::draw(&mut gl, // The OpenGL instance used to draw the GUI.
             &mut ui_context, // A user interface context keeps track of state.
             unique_id, // Each widget needs it's own UI_ID.
             Point::new(x, y), // Screen location.
             width, // Rectangle width f64.
             height, // Rectangle height f64.
             Frame(frame_width, frame_color), // Or perhaps `NoFrame` if you don't want one.
             Color::new(r, g, b, a), // The color of the rectangle.
             Label("PRESS", font_size, font_color), // Here you can pass Label(...) or NoLabel.
             || {
    // Callback closure - Do your things here!

and this is what drawing a matrix of Toggles looks like.

widget_matrix::draw(cols, // The number of columns.
                    rows, // The number of rows.
                    Point::new(x, y) // Screen location for the matrix.
                    mat_width, // Width of the matrix.
                    mat_height, // Height of the matrix.
                    |num, col, row, position, width, height| { // This is called once for each widget.

    // Now we draw the widgets with our callback params!
    toggle::draw(&mut gl, &mut ui_context, ui_id + num,
                 position, width, height,
                 Frame(frame_width, frame_color), // Rectangle frame.
                 Color::new(r, g, b, a); // Rectangle color.
                 NoLabel, // We don't feel like having a label.
                 my_value_matrix[col][row], // Toggle value (true / false)
                 |new_val| { // Our callback with the new value!
        my_value_matrix[col][row] = new_val;


There’s still heaps of room for improvement and lots to be done however it’s definitely approaching a usable state.

EDIT: There have been so many awesome suggestions since this post that we had no choice but to do a total API overhaul. Read the relevant update here!

PistonWorks - Open Source Rust Libraries!

It should be noted that there is no way Conrod would exist without the open source PistonWorks collective! Conrod has several Cargo dependencies, and they are all Piston projects! Come and visit us / join in at [GitHub] ( or drop by on Mozilla’s #rust-gamedev IRC channel where most of us are normally lurking.