diff --git a/fj-app/src/main.rs b/fj-app/src/main.rs
index 9e770c87e..7241a6376 100644
--- a/fj-app/src/main.rs
+++ b/fj-app/src/main.rs
@@ -3,31 +3,19 @@ mod camera;
 mod config;
 mod graphics;
 mod input;
+mod run;
 mod window;
 
 use std::path::PathBuf;
-use std::time::Instant;
 
 use anyhow::anyhow;
 use fj_export::export;
 use fj_host::{Model, Parameters};
 use fj_operations::shape_processor::ShapeProcessor;
-use futures::executor::block_on;
-use tracing::{trace, warn};
 use tracing_subscriber::fmt::format;
 use tracing_subscriber::EnvFilter;
-use winit::{
-    event::{Event, WindowEvent},
-    event_loop::{ControlFlow, EventLoop},
-};
 
-use crate::{
-    args::Args,
-    camera::Camera,
-    config::Config,
-    graphics::{DrawConfig, Renderer},
-    window::Window,
-};
+use crate::{args::Args, config::Config, run::run};
 
 fn main() -> anyhow::Result<()> {
     // Respect `RUST_LOG`. If that's not defined or erroneous, log warnings and
@@ -72,133 +60,7 @@ fn main() -> anyhow::Result<()> {
     }
 
     let watcher = model.load_and_watch(parameters)?;
+    run(watcher, shape_processor)?;
 
-    let event_loop = EventLoop::new();
-    let window = Window::new(&event_loop);
-
-    let mut previous_time = Instant::now();
-
-    let mut input_handler = input::Handler::new(previous_time);
-    let mut renderer = block_on(Renderer::new(&window))?;
-
-    let mut draw_config = DrawConfig::default();
-
-    let mut shape = None;
-    let mut camera = None;
-
-    event_loop.run(move |event, _, control_flow| {
-        trace!("Handling event: {:?}", event);
-
-        let mut actions = input::Actions::new();
-
-        let now = Instant::now();
-
-        if let Some(new_shape) = watcher.receive() {
-            let new_shape = shape_processor.process(&new_shape);
-            renderer.update_geometry(
-                (&new_shape.mesh).into(),
-                (&new_shape.debug_info).into(),
-                new_shape.aabb,
-            );
-
-            if camera.is_none() {
-                camera = Some(Camera::new(&new_shape.aabb));
-            }
-
-            shape = Some(new_shape);
-        }
-
-        match event {
-            Event::WindowEvent {
-                event: WindowEvent::CloseRequested,
-                ..
-            } => {
-                *control_flow = ControlFlow::Exit;
-            }
-            Event::WindowEvent {
-                event: WindowEvent::Resized(size),
-                ..
-            } => {
-                renderer.handle_resize(size);
-            }
-            Event::WindowEvent {
-                event: WindowEvent::KeyboardInput { input, .. },
-                ..
-            } => {
-                input_handler.handle_keyboard_input(input, &mut actions);
-            }
-            Event::WindowEvent {
-                event: WindowEvent::CursorMoved { position, .. },
-                ..
-            } => {
-                if let Some(camera) = &mut camera {
-                    input_handler
-                        .handle_cursor_moved(position, camera, &window);
-                }
-            }
-            Event::WindowEvent {
-                event: WindowEvent::MouseInput { state, button, .. },
-                ..
-            } => {
-                if let (Some(shape), Some(camera)) = (&shape, &camera) {
-                    let focus_point = camera.focus_point(
-                        &window,
-                        input_handler.cursor(),
-                        &shape.mesh,
-                    );
-
-                    input_handler.handle_mouse_input(
-                        button,
-                        state,
-                        focus_point,
-                    );
-                }
-            }
-            Event::WindowEvent {
-                event: WindowEvent::MouseWheel { delta, .. },
-                ..
-            } => {
-                input_handler.handle_mouse_wheel(delta, now);
-            }
-            Event::MainEventsCleared => {
-                let delta_t = now.duration_since(previous_time);
-                previous_time = now;
-
-                if let (Some(shape), Some(camera)) = (&shape, &mut camera) {
-                    input_handler.update(
-                        delta_t.as_secs_f64(),
-                        now,
-                        camera,
-                        &window,
-                        &shape.mesh,
-                    );
-                }
-
-                window.inner().request_redraw();
-            }
-            Event::RedrawRequested(_) => {
-                if let (Some(shape), Some(camera)) = (&shape, &mut camera) {
-                    camera.update_planes(&shape.aabb);
-
-                    if let Err(err) = renderer.draw(camera, &draw_config) {
-                        warn!("Draw error: {}", err);
-                    }
-                }
-            }
-            _ => {}
-        }
-
-        if actions.exit {
-            *control_flow = ControlFlow::Exit;
-        }
-        if actions.toggle_model {
-            draw_config.draw_model = !draw_config.draw_model;
-        }
-        if actions.toggle_mesh {
-            draw_config.draw_mesh = !draw_config.draw_mesh;
-        }
-        if actions.toggle_debug {
-            draw_config.draw_debug = !draw_config.draw_debug;
-        }
-    });
+    Ok(())
 }
diff --git a/fj-app/src/run.rs b/fj-app/src/run.rs
new file mode 100644
index 000000000..1d5551ea7
--- /dev/null
+++ b/fj-app/src/run.rs
@@ -0,0 +1,151 @@
+use std::time::Instant;
+
+use fj_host::Watcher;
+use fj_operations::shape_processor::ShapeProcessor;
+use futures::executor::block_on;
+use tracing::{trace, warn};
+use winit::{
+    event::{Event, WindowEvent},
+    event_loop::{ControlFlow, EventLoop},
+};
+
+use crate::{
+    camera::Camera,
+    graphics::{self, DrawConfig, Renderer},
+    input,
+    window::Window,
+};
+
+pub fn run(
+    watcher: Watcher,
+    shape_processor: ShapeProcessor,
+) -> Result<(), graphics::InitError> {
+    let event_loop = EventLoop::new();
+    let window = Window::new(&event_loop);
+
+    let mut previous_time = Instant::now();
+
+    let mut input_handler = input::Handler::new(previous_time);
+    let mut renderer = block_on(Renderer::new(&window))?;
+
+    let mut draw_config = DrawConfig::default();
+
+    let mut shape = None;
+    let mut camera = None;
+
+    event_loop.run(move |event, _, control_flow| {
+        trace!("Handling event: {:?}", event);
+
+        let mut actions = input::Actions::new();
+
+        let now = Instant::now();
+
+        if let Some(new_shape) = watcher.receive() {
+            let new_shape = shape_processor.process(&new_shape);
+            renderer.update_geometry(
+                (&new_shape.mesh).into(),
+                (&new_shape.debug_info).into(),
+                new_shape.aabb,
+            );
+
+            if camera.is_none() {
+                camera = Some(Camera::new(&new_shape.aabb));
+            }
+
+            shape = Some(new_shape);
+        }
+
+        match event {
+            Event::WindowEvent {
+                event: WindowEvent::CloseRequested,
+                ..
+            } => {
+                *control_flow = ControlFlow::Exit;
+            }
+            Event::WindowEvent {
+                event: WindowEvent::Resized(size),
+                ..
+            } => {
+                renderer.handle_resize(size);
+            }
+            Event::WindowEvent {
+                event: WindowEvent::KeyboardInput { input, .. },
+                ..
+            } => {
+                input_handler.handle_keyboard_input(input, &mut actions);
+            }
+            Event::WindowEvent {
+                event: WindowEvent::CursorMoved { position, .. },
+                ..
+            } => {
+                if let Some(camera) = &mut camera {
+                    input_handler
+                        .handle_cursor_moved(position, camera, &window);
+                }
+            }
+            Event::WindowEvent {
+                event: WindowEvent::MouseInput { state, button, .. },
+                ..
+            } => {
+                if let (Some(shape), Some(camera)) = (&shape, &camera) {
+                    let focus_point = camera.focus_point(
+                        &window,
+                        input_handler.cursor(),
+                        &shape.mesh,
+                    );
+
+                    input_handler.handle_mouse_input(
+                        button,
+                        state,
+                        focus_point,
+                    );
+                }
+            }
+            Event::WindowEvent {
+                event: WindowEvent::MouseWheel { delta, .. },
+                ..
+            } => {
+                input_handler.handle_mouse_wheel(delta, now);
+            }
+            Event::MainEventsCleared => {
+                let delta_t = now.duration_since(previous_time);
+                previous_time = now;
+
+                if let (Some(shape), Some(camera)) = (&shape, &mut camera) {
+                    input_handler.update(
+                        delta_t.as_secs_f64(),
+                        now,
+                        camera,
+                        &window,
+                        &shape.mesh,
+                    );
+                }
+
+                window.inner().request_redraw();
+            }
+            Event::RedrawRequested(_) => {
+                if let (Some(shape), Some(camera)) = (&shape, &mut camera) {
+                    camera.update_planes(&shape.aabb);
+
+                    if let Err(err) = renderer.draw(camera, &draw_config) {
+                        warn!("Draw error: {}", err);
+                    }
+                }
+            }
+            _ => {}
+        }
+
+        if actions.exit {
+            *control_flow = ControlFlow::Exit;
+        }
+        if actions.toggle_model {
+            draw_config.draw_model = !draw_config.draw_model;
+        }
+        if actions.toggle_mesh {
+            draw_config.draw_mesh = !draw_config.draw_mesh;
+        }
+        if actions.toggle_debug {
+            draw_config.draw_debug = !draw_config.draw_debug;
+        }
+    });
+}