better window bounding boxes

I also switch to using generalized Rect instead of an app for places where i was using the window boundary

src/main.rs

@@ -18,7 +18,7 @@ const PARTICLE_SIZE: f32 = 5.;
 
 struct Model {
     // Store the window ID so we can refer to this specific window later if needed.
-    _window: WindowId,
+    window: WindowId,
     // particles: Vec<Particle>,
     engine: PhysicsEngine,
 }
@@ -30,11 +30,10 @@ fn random_vec_in_rect(boundary: &Rect) -> nalgebra::Vector2<f32> {
     vector![x, y]
 }
 
-fn fill_particles(app: &App, colliders: &mut ColliderSet, bodies: &mut RigidBodySet) {
+fn fill_particles(boundary: &Rect, colliders: &mut ColliderSet, bodies: &mut RigidBodySet) {
     // Keeping track of already placed balls to avoid overlap
     // Need to look into a way to do this with rapier directly
     let mut positions: Vec<nalgebra::Vector2<f32>> = Vec::new();
-    let boundary = &app.window_rect();
 
     for _ in 0..PARTICLE_COUNT {
         let mut xy = random_vec_in_rect(boundary);
@@ -62,7 +61,7 @@ fn model(app: &App) -> Model {
     // per app
 
     // Create a new window! Store the ID so we can refer to it later.
-    let _window = app
+    let window = app
         .new_window()
         .size(WINDOW_WIDTH, WINDOW_HEIGHT)
         .title("nannou")
@@ -79,7 +78,7 @@ fn model(app: &App) -> Model {
         ..Default::default()
     };
 
-    let boundary = app.window_rect();
+    let boundary = app.window(window).unwrap().rect();
 
     /* Create the ground. */
     let collider = ColliderBuilder::cuboid(boundary.w(), 4.)
@@ -103,9 +102,13 @@ fn model(app: &App) -> Model {
         .build();
     engine.state.colliders.insert(collider);
 
-    fill_particles(app, &mut engine.state.colliders, &mut engine.state.bodies);
+    fill_particles(
+        &boundary,
+        &mut engine.state.colliders,
+        &mut engine.state.bodies,
+    );
 
-    Model { _window, engine }
+    Model { window, engine }
 }
 
 // Handle events related to the window and update the model if necessary
@@ -137,7 +140,7 @@ fn event(app: &App, model: &mut Model, event: WindowEvent) {
         }
 
         fill_particles(
-            app,
+            &app.window(model.window).unwrap().rect(),
             &mut model.engine.state.colliders,
             &mut model.engine.state.bodies,
         );