diff --git a/app-proto/src/display.rs b/app-proto/src/display.rs
index 59d0dca..14b132a 100644
--- a/app-proto/src/display.rs
+++ b/app-proto/src/display.rs
@@ -4,7 +4,6 @@ use sycamore::{prelude::*, motion::create_raf};
 use web_sys::{
     console,
     window,
-    Element,
     KeyboardEvent,
     MouseEvent,
     WebGl2RenderingContext,
@@ -15,7 +14,77 @@ use web_sys::{
     wasm_bindgen::{JsCast, JsValue}
 };
 
-use crate::{AppState, assembly::{ElementKey, ElementMotion}};
+use crate::{AppState, assembly::{Element, ElementKey, ElementColor, ElementMotion}};
+
+// --- scene data ---
+
+struct SceneSpheres {
+    representations: Vec<DVector<f64>>,
+    colors: Vec<ElementColor>,
+    highlights: Vec<f32>
+}
+
+impl SceneSpheres {
+    fn new() -> SceneSpheres{
+        SceneSpheres {
+            representations: Vec::new(),
+            colors: Vec::new(),
+            highlights: Vec::new()
+        }
+    }
+    
+    fn len_i32(&self) -> i32 {
+        self.representations.len().try_into().expect("Number of spheres must fit in a 32-bit integer")
+    }
+    
+    fn push(&mut self, representation: DVector<f64>, color: ElementColor, highlight: f32) {
+        self.representations.push(representation);
+        self.colors.push(color);
+        self.highlights.push(highlight);
+    }
+}
+
+struct ScenePoints {
+    representations: Vec<DVector<f64>>
+}
+
+impl ScenePoints {
+    fn new() -> ScenePoints {
+        ScenePoints {
+            representations: Vec::new()
+        }
+    }
+}
+
+struct Scene {
+    spheres: SceneSpheres,
+    points: ScenePoints
+}
+
+impl Scene {
+    fn new() -> Scene {
+        Scene {
+            spheres: SceneSpheres::new(),
+            points: ScenePoints::new()
+        }
+    }
+}
+
+trait DisplayItem {
+    fn show(&self, scene: &mut Scene, selected: bool);
+}
+
+impl DisplayItem for Element {
+    fn show(&self, scene: &mut Scene, selected: bool) {
+        const HIGHLIGHT: f32 = 0.2; /* SCAFFOLDING */
+        let representation = self.representation.get_clone_untracked();
+        let color = if selected { self.color.map(|channel| 0.2 + 0.8*channel) } else { self.color };
+        let highlight = if selected { 1.0 } else { HIGHLIGHT };
+        scene.spheres.push(representation, color, highlight);
+    }
+}
+
+// --- WebGL utilities ---
 
 fn compile_shader(
     context: &WebGl2RenderingContext,
@@ -140,7 +209,7 @@ fn load_new_buffer(
 
 // the direction in camera space that a mouse event is pointing along
 fn event_dir(event: &MouseEvent) -> Vector3<f64> {
-    let target: Element = event.target().unwrap().unchecked_into();
+    let target: web_sys::Element = event.target().unwrap().unchecked_into();
     let rect = target.get_bounding_client_rect();
     let width = rect.width();
     let height = rect.height();
@@ -157,6 +226,8 @@ fn event_dir(event: &MouseEvent) -> Vector3<f64> {
     )
 }
 
+// --- display component ---
+
 #[component]
 pub fn Display() -> View {
     let state = use_context::<AppState>();
@@ -225,7 +296,6 @@ pub fn Display() -> View {
         
         // display parameters
         const OPACITY: f32 = 0.5; /* SCAFFOLDING */
-        const HIGHLIGHT: f32 = 0.2; /* SCAFFOLDING */
         const LAYER_THRESHOLD: i32 = 0; /* DEBUG */
         const DEBUG_MODE: i32 = 0; /* DEBUG */
         
@@ -421,6 +491,8 @@ pub fn Display() -> View {
                 
                 // --- get the assembly ---
                 
+                let mut scene = Scene::new();
+                
                 // find the map from assembly space to world space
                 let location = {
                     let u = -location_z;
@@ -435,50 +507,24 @@ pub fn Display() -> View {
                 let asm_to_world = &location * &orientation;
                 
                 // get the spheres
-                let (
-                    sphere_cnt,
-                    sphere_reps_world,
-                    sphere_colors,
-                    sphere_highlights
-                ) = state.assembly.elements.with(|elts| {
-                    (
-                        // number of elements
-                        elts.len() as i32,
-                        
-                        // representation vectors in world coordinates
-                        elts.iter().map(
-                            |(_, elt)| elt.representation.with(|rep| &asm_to_world * rep)
-                        ).collect::<Vec<_>>(),
-                        
-                        // colors
-                        elts.iter().map(|(key, elt)| {
-                            if state.selection.with(|sel| sel.contains(&key)) {
-                                elt.color.map(|ch| 0.2 + 0.8*ch)
-                            } else {
-                                elt.color
-                            }
-                        }).collect::<Vec<_>>(),
-                        
-                        // highlight levels
-                        elts.iter().map(|(key, _)| {
-                            if state.selection.with(|sel| sel.contains(&key)) {
-                                1.0_f32
-                            } else {
-                                HIGHLIGHT
-                            }
-                        }).collect::<Vec<_>>()
-                    )
-                });
+                state.assembly.elements.with_untracked(
+                    |elts| for (key, elt) in elts {
+                        let selected = state.selection.with(|sel| sel.contains(&key));
+                        elt.show(&mut scene, selected);
+                    }
+                );
+                let sphere_cnt = scene.spheres.len_i32();
+                
+                // write the spheres in world coordinates
+                let sphere_reps_world: Vec<_> = scene.spheres.representations.into_iter().map(
+                    |rep| &asm_to_world * rep
+                ).collect();
                 
                 /* SCAFFOLDING */
                 // get the points
-                let point_positions = {
+                scene.points.representations.append({
                     use crate::engine::point;
-                    
-                    /* DEBUG */
-                    // hard-code the origin and the centers of the spheres in
-                    // the general test assembly
-                    let point_reps = [
+                    &mut vec![
                         point(0.0, 0.0, 0.0),
                         point(0.5, 0.5, 0.0),
                         point(-0.5, -0.5, 0.0),
@@ -486,12 +532,16 @@ pub fn Display() -> View {
                         point(0.5, -0.5, 0.0),
                         point(0.0, 0.15, 1.0),
                         point(0.0, -0.15, -1.0)
-                    ];
-                    
-                    let asm_to_world_sp = asm_to_world.rows(0, SPACE_DIM);
-                    let point_reps_world_sp = point_reps.map(|rep| &asm_to_world_sp * rep);
-                    DMatrix::from_columns(&point_reps_world_sp).cast::<f32>()
-                };
+                    ]
+                });
+                
+                // write the points in world coordinates
+                let asm_to_world_sp = asm_to_world.rows(0, SPACE_DIM);
+                let point_positions = DMatrix::from_columns(
+                    &scene.points.representations.into_iter().map(
+                        |rep| &asm_to_world_sp * rep
+                    ).collect::<Vec<_>>().as_slice()
+                ).cast::<f32>();
                 
                 // --- draw the spheres ---
                 
@@ -518,11 +568,11 @@ pub fn Display() -> View {
                     );
                     ctx.uniform3fv_with_f32_array(
                         sphere_color_locs[n].as_ref(),
-                        &sphere_colors[n]
+                        &scene.spheres.colors[n]
                     );
                     ctx.uniform1f(
                         sphere_highlight_locs[n].as_ref(),
-                        sphere_highlights[n]
+                        scene.spheres.highlights[n]
                     );
                 }