Radial tree + Forces

.gitignore

@@ -0,0 +1,2 @@
+.direnv/
+.envrc

Dockerfile

@@ -0,0 +1,18 @@
+FROM node:lts-alpine
+
+WORKDIR /app
+
+# Copy dependency definitions
+COPY package*.json ./
+
+# Install dependencies
+RUN npm install
+
+# Copy the rest of the source code
+COPY . .
+
+# Expose the standard Vite port
+EXPOSE 5173
+
+# Compute layout, then start the dev server with --host for external access
+CMD ["sh", "-c", "npm run layout && npm run dev -- --host"]

docker-compose.yml

@@ -0,0 +1,9 @@
+services:
+  app:
+    build: .
+    ports:
+      - "5173:5173"
+    command: sh -c "npx tsx scripts/compute_layout.ts && npm run dev -- --host"
+    volumes:
+      - .:/app
+      - /app/node_modules # Prevents local node_modules from overwriting the container's

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1770464364,
+        "narHash": "sha256-z5NJPSBwsLf/OfD8WTmh79tlSU8XgIbwmk6qB1/TFzY=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "23d72dabcb3b12469f57b37170fcbc1789bd7457",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-25.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,28 @@
+{
+  description = "basic";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11";
+  };
+
+  outputs = { self, nixpkgs, ... }: 
+    let
+      system = "x86_64-linux";
+      pkgs = import nixpkgs {
+        inherit system;
+        config = { allowUnfree = true; };
+      };
+      
+      myJdk = pkgs.openjdk11; # Simplified reference, usually aliases correctly
+    in
+      {
+        devShell.x86_64-linux = pkgs.mkShell {
+          packages = [
+          	pkgs.vscode-fhs
+          	pkgs.antigravity-fhs
+            pkgs.bashInteractive 
+          ];
+
+        };
+      };
+}

package.json

@@ -6,7 +6,8 @@
   "scripts": {
     "dev": "vite",
     "build": "vite build",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "layout": "tsx scripts/compute_layout.ts"
   },
   "dependencies": {
     "@webgpu/types": "^0.1.69",
@@ -23,7 +24,8 @@
     "@vitejs/plugin-react": "5.1.1",
     "tailwindcss": "4.1.17",
     "typescript": "5.9.3",
+    "tsx": "^4.0.0",
     "vite": "7.2.4",
     "vite-plugin-singlefile": "2.3.0"
   }
-}
+}

scripts/compute_layout.ts

@@ -0,0 +1,354 @@
+#!/usr/bin/env npx tsx
+/**
+ * Tree-Aware Force Layout
+ *
+ * Generates a random tree (via generate_tree), computes a radial tree layout,
+ * then applies gentle force refinement and writes node_positions.csv.
+ *
+ * Usage: npm run layout
+ */
+
+import { writeFileSync } from "fs";
+import { join, dirname } from "path";
+import { fileURLToPath } from "url";
+import { generateTree } from "./generate_tree.js";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const PUBLIC_DIR = join(__dirname, "..", "public");
+
+// ══════════════════════════════════════════════════════════
+// Configuration
+// ══════════════════════════════════════════════════════════
+
+const ENABLE_FORCE_SIM = true;  // Set to false to skip force simulation
+const ITERATIONS = 100;        // Force iterations (gentle)
+const REPULSION_K = 80;        // Repulsion strength (1% of original 8000)
+const EDGE_LENGTH = 120;       // Desired edge rest length
+const ATTRACTION_K = 0.0002;   // Spring stiffness for edges (1% of original 0.02)
+const THETA = 0.7;             // Barnes-Hut accuracy
+const INITIAL_MAX_DISP = 15;   // Starting max displacement
+const COOLING = 0.998;         // Very slow cooling per iteration
+const MIN_DIST = 0.5;
+const PRINT_EVERY = 10;        // Print progress every N iterations
+
+// Scale radius so the tree is nicely spread
+const RADIUS_PER_DEPTH = EDGE_LENGTH * 1.2;
+
+// ── Special nodes with longer parent-edges ──
+// Add vertex IDs here to give them longer edges to their parent.
+// These nodes (and all their descendants) will be pushed further out.
+const LONG_EDGE_NODES = new Set<number>([
+    // e.g. 42, 99, 150
+]);
+const LONG_EDGE_MULTIPLIER = 3.0;  // How many times longer than normal
+
+// ══════════════════════════════════════════════════════════
+// Generate tree (in-memory)
+// ══════════════════════════════════════════════════════════
+
+const { root, nodeCount: N, childrenOf, parentOf } = generateTree();
+
+const nodeIds: number[] = [];
+for (let i = 0; i < N; i++) nodeIds.push(i);
+
+// Dense index mapping (identity since IDs are 0..N-1)
+const idToIdx = new Map<number, number>();
+for (let i = 0; i < N; i++) idToIdx.set(i, i);
+
+// Edge list as index pairs (child, parent)
+const edges: Array<[number, number]> = [];
+for (const [child, parent] of parentOf) {
+    edges.push([child, parent]);
+}
+
+// Per-node neighbor list (for edge traversal)
+const neighbors: number[][] = Array.from({ length: N }, () => []);
+for (const [a, b] of edges) {
+    neighbors[a].push(b);
+    neighbors[b].push(a);
+}
+
+console.log(`Tree: ${N} nodes, ${edges.length} edges, root=${root}`);
+
+// ══════════════════════════════════════════════════════════
+// Step 1: Radial tree layout (generous spacing, no crossings)
+// ══════════════════════════════════════════════════════════
+
+const x = new Float64Array(N);
+const y = new Float64Array(N);
+const depth = new Uint32Array(N);
+const nodeRadius = new Float64Array(N); // cumulative radius from root
+
+// Compute subtree sizes
+const subtreeSize = new Uint32Array(N).fill(1);
+{
+    const rootIdx = idToIdx.get(root)!;
+    const stack: Array<{ idx: number; phase: "enter" | "exit" }> = [
+        { idx: rootIdx, phase: "enter" },
+    ];
+    while (stack.length > 0) {
+        const { idx, phase } = stack.pop()!;
+        if (phase === "enter") {
+            stack.push({ idx, phase: "exit" });
+            const kids = childrenOf.get(nodeIds[idx]);
+            if (kids) {
+                for (const kid of kids) {
+                    stack.push({ idx: idToIdx.get(kid)!, phase: "enter" });
+                }
+            }
+        } else {
+            const kids = childrenOf.get(nodeIds[idx]);
+            if (kids) {
+                for (const kid of kids) {
+                    subtreeSize[idx] += subtreeSize[idToIdx.get(kid)!];
+                }
+            }
+        }
+    }
+}
+
+// Compute depths & max depth
+let maxDepth = 0;
+{
+    const rootIdx = idToIdx.get(root)!;
+    const stack: Array<{ idx: number; d: number }> = [{ idx: rootIdx, d: 0 }];
+    while (stack.length > 0) {
+        const { idx, d } = stack.pop()!;
+        depth[idx] = d;
+        if (d > maxDepth) maxDepth = d;
+        const kids = childrenOf.get(nodeIds[idx]);
+        if (kids) {
+            for (const kid of kids) {
+                stack.push({ idx: idToIdx.get(kid)!, d: d + 1 });
+            }
+        }
+    }
+}
+
+// BFS radial assignment (cumulative radii to support per-edge lengths)
+{
+    const rootIdx = idToIdx.get(root)!;
+    x[rootIdx] = 0;
+    y[rootIdx] = 0;
+    nodeRadius[rootIdx] = 0;
+
+    interface Entry {
+        idx: number;
+        d: number;
+        aStart: number;
+        aEnd: number;
+    }
+
+    const queue: Entry[] = [{ idx: rootIdx, d: 0, aStart: 0, aEnd: 2 * Math.PI }];
+    let head = 0;
+
+    while (head < queue.length) {
+        const { idx, d, aStart, aEnd } = queue[head++];
+        const kids = childrenOf.get(nodeIds[idx]);
+        if (!kids || kids.length === 0) continue;
+
+        // Sort children by subtree size (largest sectors together for balance)
+        const sortedKids = [...kids].sort(
+            (a, b) => (subtreeSize[idToIdx.get(b)!]) - (subtreeSize[idToIdx.get(a)!])
+        );
+
+        const totalWeight = sortedKids.reduce(
+            (s, k) => s + subtreeSize[idToIdx.get(k)!], 0
+        );
+
+        let angle = aStart;
+        for (const kid of sortedKids) {
+            const kidIdx = idToIdx.get(kid)!;
+            const w = subtreeSize[kidIdx];
+            const sector = (w / totalWeight) * (aEnd - aStart);
+            const mid = angle + sector / 2;
+
+            // Cumulative radius: parent's radius + edge step (longer for special nodes)
+            const step = LONG_EDGE_NODES.has(kid)
+                ? RADIUS_PER_DEPTH * LONG_EDGE_MULTIPLIER
+                : RADIUS_PER_DEPTH;
+            const r = nodeRadius[idx] + step;
+            nodeRadius[kidIdx] = r;
+
+            x[kidIdx] = r * Math.cos(mid);
+            y[kidIdx] = r * Math.sin(mid);
+
+            queue.push({ idx: kidIdx, d: d + 1, aStart: angle, aEnd: angle + sector });
+            angle += sector;
+        }
+    }
+}
+
+console.log(`Radial layout done (depth=${maxDepth}, radius_step=${RADIUS_PER_DEPTH})`);
+
+// ══════════════════════════════════════════════════════════
+// Step 2: Gentle force refinement (preserves non-crossing)
+// ══════════════════════════════════════════════════════════
+
+// Barnes-Hut quadtree for repulsion
+interface BHNode {
+    cx: number; cy: number;
+    mass: number;
+    size: number;
+    children: (BHNode | null)[];
+    bodyIdx: number;
+}
+
+function buildBHTree(): BHNode {
+    let minX = Infinity, maxX = -Infinity, minY = Infinity, maxY = -Infinity;
+    for (let i = 0; i < N; i++) {
+        if (x[i] < minX) minX = x[i];
+        if (x[i] > maxX) maxX = x[i];
+        if (y[i] < minY) minY = y[i];
+        if (y[i] > maxY) maxY = y[i];
+    }
+    const size = Math.max(maxX - minX, maxY - minY, 1) * 1.01;
+    const cx = (minX + maxX) / 2;
+    const cy = (minY + maxY) / 2;
+
+    const root: BHNode = {
+        cx: 0, cy: 0, mass: 0, size,
+        children: [null, null, null, null], bodyIdx: -1,
+    };
+
+    for (let i = 0; i < N; i++) {
+        insert(root, i, cx, cy, size);
+    }
+    return root;
+}
+
+function insert(node: BHNode, idx: number, ncx: number, ncy: number, ns: number): void {
+    if (node.mass === 0) {
+        node.bodyIdx = idx;
+        node.cx = x[idx]; node.cy = y[idx];
+        node.mass = 1;
+        return;
+    }
+    if (node.bodyIdx >= 0) {
+        const old = node.bodyIdx;
+        node.bodyIdx = -1;
+        putInQuadrant(node, old, ncx, ncy, ns);
+    }
+    putInQuadrant(node, idx, ncx, ncy, ns);
+    const tm = node.mass + 1;
+    node.cx = (node.cx * node.mass + x[idx]) / tm;
+    node.cy = (node.cy * node.mass + y[idx]) / tm;
+    node.mass = tm;
+}
+
+function putInQuadrant(node: BHNode, idx: number, ncx: number, ncy: number, ns: number): void {
+    const hs = ns / 2;
+    const qx = x[idx] >= ncx ? 1 : 0;
+    const qy = y[idx] >= ncy ? 1 : 0;
+    const q = qy * 2 + qx;
+    const ccx = ncx + (qx ? hs / 2 : -hs / 2);
+    const ccy = ncy + (qy ? hs / 2 : -hs / 2);
+    if (!node.children[q]) {
+        node.children[q] = {
+            cx: 0, cy: 0, mass: 0, size: hs,
+            children: [null, null, null, null], bodyIdx: -1,
+        };
+    }
+    insert(node.children[q]!, idx, ccx, ccy, hs);
+}
+
+function repulse(node: BHNode, idx: number, fx: Float64Array, fy: Float64Array): void {
+    if (node.mass === 0 || node.bodyIdx === idx) return;
+    const dx = x[idx] - node.cx;
+    const dy = y[idx] - node.cy;
+    const d2 = dx * dx + dy * dy;
+    const d = Math.sqrt(d2) || MIN_DIST;
+
+    if (node.bodyIdx >= 0 || (node.size / d) < THETA) {
+        const f = REPULSION_K * node.mass / (d2 + MIN_DIST);
+        fx[idx] += (dx / d) * f;
+        fy[idx] += (dy / d) * f;
+        return;
+    }
+    for (const c of node.children) {
+        if (c) repulse(c, idx, fx, fy);
+    }
+}
+
+// ── Force simulation ──
+if (ENABLE_FORCE_SIM) {
+    console.log(`Applying gentle forces (${ITERATIONS} steps, 1% strength)...`);
+    const t0 = performance.now();
+    let maxDisp = INITIAL_MAX_DISP;
+
+    for (let iter = 0; iter < ITERATIONS; iter++) {
+        const fx = new Float64Array(N);
+        const fy = new Float64Array(N);
+
+        // 1. Repulsion
+        const tree = buildBHTree();
+        for (let i = 0; i < N; i++) {
+            repulse(tree, i, fx, fy);
+        }
+
+        // 2. Edge attraction (spring toward per-edge rest length)
+        for (const [a, b] of edges) {
+            const dx = x[b] - x[a];
+            const dy = y[b] - y[a];
+            const d = Math.sqrt(dx * dx + dy * dy) || MIN_DIST;
+            const aId = nodeIds[a], bId = nodeIds[b];
+            const isLong = LONG_EDGE_NODES.has(aId) || LONG_EDGE_NODES.has(bId);
+            const restLen = isLong ? EDGE_LENGTH * LONG_EDGE_MULTIPLIER : EDGE_LENGTH;
+            const displacement = d - restLen;
+            const f = ATTRACTION_K * displacement;
+            const ux = dx / d, uy = dy / d;
+            fx[a] += ux * f;
+            fy[a] += uy * f;
+            fx[b] -= ux * f;
+            fy[b] -= uy * f;
+        }
+
+        // 3. Apply forces with displacement cap (cooling reduces it over time)
+        for (let i = 0; i < N; i++) {
+            const mag = Math.sqrt(fx[i] * fx[i] + fy[i] * fy[i]);
+            if (mag > 0) {
+                const cap = Math.min(maxDisp, mag) / mag;
+                x[i] += fx[i] * cap;
+                y[i] += fy[i] * cap;
+            }
+        }
+
+        // 4. Cool down
+        maxDisp *= COOLING;
+
+        if ((iter + 1) % PRINT_EVERY === 0) {
+            let totalForce = 0;
+            for (let i = 0; i < N; i++) totalForce += Math.sqrt(fx[i] * fx[i] + fy[i] * fy[i]);
+            console.log(`  iter ${iter + 1}/${ITERATIONS}  max_disp=${maxDisp.toFixed(2)}  avg_force=${(totalForce / N).toFixed(2)}`);
+        }
+    }
+
+    const elapsed = performance.now() - t0;
+    console.log(`Force simulation done in ${(elapsed / 1000).toFixed(1)}s`);
+} else {
+    console.log("Force simulation SKIPPED (ENABLE_FORCE_SIM = false)");
+}
+
+// ══════════════════════════════════════════════════════════
+// Write output
+// ══════════════════════════════════════════════════════════
+
+// Write node positions
+const outLines: string[] = ["vertex,x,y"];
+for (let i = 0; i < N; i++) {
+    outLines.push(`${nodeIds[i]},${x[i]},${y[i]}`);
+}
+
+const outPath = join(PUBLIC_DIR, "node_positions.csv");
+writeFileSync(outPath, outLines.join("\n") + "\n");
+console.log(`Wrote ${N} positions to ${outPath}`);
+
+// Write edges (so the renderer can draw them)
+const edgeLines: string[] = ["source,target"];
+for (const [child, parent] of parentOf) {
+    edgeLines.push(`${child},${parent}`);
+}
+
+const edgesPath = join(PUBLIC_DIR, "edges.csv");
+writeFileSync(edgesPath, edgeLines.join("\n") + "\n");
+console.log(`Wrote ${edges.length} edges to ${edgesPath}`);

scripts/generate_tree.ts

@@ -0,0 +1,61 @@
+/**
+ * Random Tree Generator
+ *
+ * Generates a random tree with 1–MAX_CHILDREN children per node.
+ * Exports a function that returns the tree data in memory.
+ */
+
+// ══════════════════════════════════════════════════════════
+// Configuration
+// ══════════════════════════════════════════════════════════
+
+const TARGET_NODES = 100000;      // Approximate number of nodes to generate
+const MAX_CHILDREN = 3;        // Each node gets 1..MAX_CHILDREN children
+
+// ══════════════════════════════════════════════════════════
+// Tree data types
+// ══════════════════════════════════════════════════════════
+
+export interface TreeData {
+    root: number;
+    nodeCount: number;
+    childrenOf: Map<number, number[]>;
+    parentOf: Map<number, number>;
+}
+
+// ══════════════════════════════════════════════════════════
+// Generator
+// ══════════════════════════════════════════════════════════
+
+export function generateTree(): TreeData {
+    const childrenOf = new Map<number, number[]>();
+    const parentOf = new Map<number, number>();
+
+    const root = 0;
+    let nextId = 1;
+    const queue: number[] = [root];
+    let head = 0;
+
+    while (head < queue.length && nextId < TARGET_NODES) {
+        const parent = queue[head++];
+        const nKids = 1 + Math.floor(Math.random() * MAX_CHILDREN); // 1..MAX_CHILDREN
+
+        const kids: number[] = [];
+        for (let c = 0; c < nKids && nextId < TARGET_NODES; c++) {
+            const child = nextId++;
+            kids.push(child);
+            parentOf.set(child, parent);
+            queue.push(child);
+        }
+        childrenOf.set(parent, kids);
+    }
+
+    console.log(`Generated tree: ${nextId} nodes, ${parentOf.size} edges, root=${root}`);
+
+    return {
+        root,
+        nodeCount: nextId,
+        childrenOf,
+        parentOf,
+    };
+}

src/App.tsx

@@ -3,7 +3,9 @@ import { Renderer } from "./renderer";
 
 export default function App() {
   const canvasRef = useRef<HTMLCanvasElement>(null);
-  const [status, setStatus] = useState("Generating 10M particles & building spatial index…");
+  const rendererRef = useRef<Renderer | null>(null);
+  const [status, setStatus] = useState("Loading node positions…");
+  const [nodeCount, setNodeCount] = useState(0);
   const [stats, setStats] = useState({
     fps: 0,
     drawn: 0,
@@ -12,6 +14,11 @@ export default function App() {
     ptSize: 0,
   });
   const [error, setError] = useState("");
+  const [hoveredNode, setHoveredNode] = useState<{ x: number; y: number; screenX: number; screenY: number } | null>(null);
+  const [selectedNodes, setSelectedNodes] = useState<Set<number>>(new Set());
+
+  // Store mouse position in a ref so it can be accessed in render loop without re-renders
+  const mousePos = useRef({ x: 0, y: 0 });
 
   useEffect(() => {
     const canvas = canvasRef.current;
@@ -20,45 +27,135 @@ export default function App() {
     let renderer: Renderer;
     try {
       renderer = new Renderer(canvas);
+      rendererRef.current = renderer;
     } catch (e) {
       setError(e instanceof Error ? e.message : String(e));
       return;
     }
 
-    // Build quadtree + upload (runs once, ~200ms)
+    let cancelled = false;
-    const buildMs = renderer.init();
+
-    setStatus("");
+    // Fetch CSVs, parse, and init renderer
-    console.log(`Init complete in ${buildMs.toFixed(0)}ms`);
+    (async () => {
+      try {
+        setStatus("Fetching data files…");
+        const [nodesResponse, edgesResponse] = await Promise.all([
+          fetch("/node_positions.csv"),
+          fetch("/edges.csv"),
+        ]);
+        if (!nodesResponse.ok) throw new Error(`Failed to fetch nodes: ${nodesResponse.status}`);
+        if (!edgesResponse.ok) throw new Error(`Failed to fetch edges: ${edgesResponse.status}`);
+
+        const [nodesText, edgesText] = await Promise.all([
+          nodesResponse.text(),
+          edgesResponse.text(),
+        ]);
+        if (cancelled) return;
+
+        setStatus("Parsing positions…");
+        const nodeLines = nodesText.split("\n").slice(1).filter(l => l.trim().length > 0);
+        const count = nodeLines.length;
+
+        const xs = new Float32Array(count);
+        const ys = new Float32Array(count);
+        const vertexIds = new Uint32Array(count);
+        for (let i = 0; i < count; i++) {
+          const parts = nodeLines[i].split(",");
+          vertexIds[i] = parseInt(parts[0], 10);
+          xs[i] = parseFloat(parts[1]);
+          ys[i] = parseFloat(parts[2]);
+        }
+
+        setStatus("Parsing edges…");
+        const edgeLines = edgesText.split("\n").slice(1).filter(l => l.trim().length > 0);
+        const edgeData = new Uint32Array(edgeLines.length * 2);
+        for (let i = 0; i < edgeLines.length; i++) {
+          const parts = edgeLines[i].split(",");
+          edgeData[i * 2] = parseInt(parts[0], 10);
+          edgeData[i * 2 + 1] = parseInt(parts[1], 10);
+        }
+
+        if (cancelled) return;
+
+        setStatus("Building spatial index…");
+        await new Promise(r => setTimeout(r, 0));
+
+        const buildMs = renderer.init(xs, ys, vertexIds, edgeData);
+        setNodeCount(renderer.getNodeCount());
+        setStatus("");
+        console.log(`Init complete: ${count.toLocaleString()} nodes, ${edgeLines.length.toLocaleString()} edges in ${buildMs.toFixed(0)}ms`);
+      } catch (e) {
+        if (!cancelled) {
+          setError(e instanceof Error ? e.message : String(e));
+        }
+      }
+    })();
 
     // ── Input handling ──
     let dragging = false;
+    let didDrag = false; // true if mouse moved significantly during drag
+    let downX = 0;
+    let downY = 0;
     let lastX = 0;
     let lastY = 0;
+    const DRAG_THRESHOLD = 5; // pixels
 
     const onDown = (e: MouseEvent) => {
       dragging = true;
+      didDrag = false;
+      downX = e.clientX;
+      downY = e.clientY;
       lastX = e.clientX;
       lastY = e.clientY;
     };
     const onMove = (e: MouseEvent) => {
+      mousePos.current = { x: e.clientX, y: e.clientY };
       if (!dragging) return;
+
+      // Check if we've moved enough to consider it a drag
+      const dx = e.clientX - downX;
+      const dy = e.clientY - downY;
+      if (Math.abs(dx) > DRAG_THRESHOLD || Math.abs(dy) > DRAG_THRESHOLD) {
+        didDrag = true;
+      }
+
       renderer.pan(e.clientX - lastX, e.clientY - lastY);
       lastX = e.clientX;
       lastY = e.clientY;
     };
-    const onUp = () => {
+    const onUp = (e: MouseEvent) => {
+      if (dragging && !didDrag) {
+        // This was a click, not a drag - handle selection
+        const node = renderer.findNodeIndexAt(e.clientX, e.clientY);
+        if (node) {
+          setSelectedNodes((prev: Set<number>) => {
+            const next = new Set(prev);
+            if (next.has(node.index)) {
+              next.delete(node.index); // Deselect if already selected
+            } else {
+              next.add(node.index); // Select
+            }
+            return next;
+          });
+        }
+      }
       dragging = false;
+      didDrag = false;
     };
     const onWheel = (e: WheelEvent) => {
       e.preventDefault();
       const factor = e.deltaY > 0 ? 0.9 : 1 / 0.9;
       renderer.zoomAt(factor, e.clientX, e.clientY);
     };
+    const onMouseLeave = () => {
+      setHoveredNode(null);
+    };
 
     canvas.addEventListener("mousedown", onDown);
     window.addEventListener("mousemove", onMove);
     window.addEventListener("mouseup", onUp);
     canvas.addEventListener("wheel", onWheel, { passive: false });
+    canvas.addEventListener("mouseleave", onMouseLeave);
 
     // ── Render loop ──
     let frameCount = 0;
@@ -69,6 +166,14 @@ export default function App() {
       const result = renderer.render();
       frameCount++;
 
+      // Find hovered node using quadtree
+      const node = renderer.findNodeAt(mousePos.current.x, mousePos.current.y);
+      if (node) {
+        setHoveredNode({ ...node, screenX: mousePos.current.x, screenY: mousePos.current.y });
+      } else {
+        setHoveredNode(null);
+      }
+
       const now = performance.now();
       if (now - lastTime >= 500) {
         const fps = (frameCount / (now - lastTime)) * 1000;
@@ -88,14 +193,23 @@ export default function App() {
     raf = requestAnimationFrame(frame);
 
     return () => {
+      cancelled = true;
       cancelAnimationFrame(raf);
       canvas.removeEventListener("mousedown", onDown);
       window.removeEventListener("mousemove", onMove);
       window.removeEventListener("mouseup", onUp);
       canvas.removeEventListener("wheel", onWheel);
+      canvas.removeEventListener("mouseleave", onMouseLeave);
     };
   }, []);
 
+  // Sync selection state to renderer
+  useEffect(() => {
+    if (rendererRef.current) {
+      rendererRef.current.updateSelection(selectedNodes);
+    }
+  }, [selectedNodes]);
+
   return (
     <div style={{ width: "100vw", height: "100vh", overflow: "hidden", background: "#000" }}>
       <canvas
@@ -160,10 +274,11 @@ export default function App() {
             }}
           >
             <div>FPS: {stats.fps}</div>
-            <div>Drawn: {stats.drawn.toLocaleString()} / 10,000,000</div>
+            <div>Drawn: {stats.drawn.toLocaleString()} / {nodeCount.toLocaleString()}</div>
             <div>Mode: {stats.mode}</div>
             <div>Zoom: {stats.zoom < 0.01 ? stats.zoom.toExponential(2) : stats.zoom.toFixed(2)} px/unit</div>
             <div>Pt Size: {stats.ptSize.toFixed(1)}px</div>
+            <div style={{ color: "#f80" }}>Selected: {selectedNodes.size}</div>
           </div>
           <div
             style={{
@@ -179,8 +294,31 @@ export default function App() {
               pointerEvents: "none",
             }}
           >
-            Drag to pan · Scroll to zoom
+            Drag to pan · Scroll to zoom · Click to select
           </div>
+
+          {/* Hover tooltip */}
+          {hoveredNode && (
+            <div
+              style={{
+                position: "absolute",
+                left: hoveredNode.screenX + 15,
+                top: hoveredNode.screenY + 15,
+                background: "rgba(0,0,0,0.85)",
+                color: "#0ff",
+                fontFamily: "monospace",
+                padding: "6px 10px",
+                fontSize: "12px",
+                borderRadius: "4px",
+                pointerEvents: "none",
+                whiteSpace: "nowrap",
+                border: "1px solid rgba(0,255,255,0.3)",
+                boxShadow: "0 2px 8px rgba(0,0,0,0.5)",
+              }}
+            >
+              ({hoveredNode.x.toFixed(2)}, {hoveredNode.y.toFixed(2)})
+            </div>
+          )}
         </>
       )}
     </div>

src/quadtree.ts

@@ -23,7 +23,7 @@ export interface Leaf {
 export function buildSpatialIndex(
   xs: Float32Array,
   ys: Float32Array
-): { sorted: Float32Array; leaves: Leaf[] } {
+): { sorted: Float32Array; leaves: Leaf[]; order: Uint32Array } {
   const n = xs.length;
   const order = new Uint32Array(n);
   for (let i = 0; i < n; i++) order[i] = i;
@@ -109,5 +109,5 @@ export function buildSpatialIndex(
     sorted[i * 2 + 1] = ys[src];
   }
 
-  return { sorted, leaves };
+  return { sorted, leaves, order };
 }

src/renderer.ts

@@ -32,6 +32,26 @@ void main() {
 }
 `;
 
+const SELECTED_FRAG = `#version 300 es
+precision mediump float;
+out vec4 o;
+void main() {
+  vec2 c = gl_PointCoord * 2.0 - 1.0;
+  if (dot(c, c) > 1.0) discard;
+  o = vec4(1.0, 0.5, 0.0, 0.9); // orange for selected
+}
+`;
+
+const NEIGHBOR_FRAG = `#version 300 es
+precision mediump float;
+out vec4 o;
+void main() {
+  vec2 c = gl_PointCoord * 2.0 - 1.0;
+  if (dot(c, c) > 1.0) discard;
+  o = vec4(1.0, 0.9, 0.0, 0.8); // yellow for neighbors
+}
+`;
+
 /* ── Types ──────────────────────────────────────────────── */
 
 export interface RenderStats {
@@ -43,10 +63,8 @@ export interface RenderStats {
 
 /* ── Constants ──────────────────────────────────────────── */
 
-const COUNT = 10_000_000;
-const EXTENT = 30_000; // particles span [-15000, 15000]
 const WORLD_RADIUS = 4.0; // sphere world-space radius
-const MAX_DRAW = 600_000; // max particles to draw per frame
+const MAX_DRAW = 2_000_000; // max particles to draw per frame
 
 /* ── Renderer ───────────────────────────────────────────── */
 
@@ -55,10 +73,18 @@ export class Renderer {
   private canvas: HTMLCanvasElement;
   private program: WebGLProgram;
   private lineProgram: WebGLProgram;
+  private selectedProgram: WebGLProgram;
+  private neighborProgram: WebGLProgram;
   private vao: WebGLVertexArrayObject;
 
   // Data
   private leaves: Leaf[] = [];
+  private sorted: Float32Array = new Float32Array(0);
+  private nodeCount = 0;
+  private edgeCount = 0;
+  private neighborMap: Map<number, number[]> = new Map();
+  private leafEdgeStarts: Uint32Array = new Uint32Array(0);
+  private leafEdgeCounts: Uint32Array = new Uint32Array(0);
   private maxPtSize = 256;
 
   // Multi-draw extension
@@ -71,12 +97,28 @@ export class Renderer {
   private uCenter: WebGLUniformLocation;
   private uScale: WebGLUniformLocation;
   private uPtSize: WebGLUniformLocation;
-  
+
   private uCenterLine: WebGLUniformLocation;
   private uScaleLine: WebGLUniformLocation;
-  
+
+  private uCenterSelected: WebGLUniformLocation;
+  private uScaleSelected: WebGLUniformLocation;
+  private uPtSizeSelected: WebGLUniformLocation;
+
+  private uCenterNeighbor: WebGLUniformLocation;
+  private uScaleNeighbor: WebGLUniformLocation;
+  private uPtSizeNeighbor: WebGLUniformLocation;
+
   private linesIbo: WebGLBuffer;
 
+  // Selection
+  private selectionIbo: WebGLBuffer;
+  private selectionCount = 0;
+
+  // Neighbors
+  private neighborIbo: WebGLBuffer;
+  private neighborCount = 0;
+
   // Camera state
   private cx = 0;
   private cy = 0;
@@ -93,16 +135,26 @@ export class Renderer {
     // Compile programs
     this.program = this.compileProgram(VERT, FRAG);
     this.lineProgram = this.compileProgram(VERT, LINE_FRAG);
-    
+    this.selectedProgram = this.compileProgram(VERT, SELECTED_FRAG);
+    this.neighborProgram = this.compileProgram(VERT, NEIGHBOR_FRAG);
+
     gl.useProgram(this.program);
 
     this.uCenter = gl.getUniformLocation(this.program, "u_center")!;
     this.uScale = gl.getUniformLocation(this.program, "u_scale")!;
     this.uPtSize = gl.getUniformLocation(this.program, "u_ptSize")!;
-    
+
     this.uCenterLine = gl.getUniformLocation(this.lineProgram, "u_center")!;
     this.uScaleLine = gl.getUniformLocation(this.lineProgram, "u_scale")!;
 
+    this.uCenterSelected = gl.getUniformLocation(this.selectedProgram, "u_center")!;
+    this.uScaleSelected = gl.getUniformLocation(this.selectedProgram, "u_scale")!;
+    this.uPtSizeSelected = gl.getUniformLocation(this.selectedProgram, "u_ptSize")!;
+
+    this.uCenterNeighbor = gl.getUniformLocation(this.neighborProgram, "u_center")!;
+    this.uScaleNeighbor = gl.getUniformLocation(this.neighborProgram, "u_scale")!;
+    this.uPtSizeNeighbor = gl.getUniformLocation(this.neighborProgram, "u_ptSize")!;
+
     // Query hardware max point size
     const range = gl.getParameter(gl.ALIASED_POINT_SIZE_RANGE) as Float32Array;
     this.maxPtSize = range[1] || 256;
@@ -112,13 +164,15 @@ export class Renderer {
     gl.bindVertexArray(this.vao);
     const vbo = gl.createBuffer()!;
     gl.bindBuffer(gl.ARRAY_BUFFER, vbo);
-    
+
     // We forced a_pos to location 0 in compileProgram
     gl.enableVertexAttribArray(0);
     gl.vertexAttribPointer(0, 2, gl.FLOAT, false, 0, 0);
     gl.bindVertexArray(null);
-    
+
     this.linesIbo = gl.createBuffer()!;
+    this.selectionIbo = gl.createBuffer()!;
+    this.neighborIbo = gl.createBuffer()!;
 
     // Blending
     gl.enable(gl.BLEND);
@@ -127,24 +181,27 @@ export class Renderer {
   }
 
   /**
-   * Generate 10M random particles, build quadtree, upload to GPU.
+   * Load particles from pre-computed positions and edges, build quadtree, upload to GPU.
+   * vertexIds: original vertex IDs from CSV (parallel to xs/ys)
+   * edges: flat array of [srcVertexId, dstVertexId, ...]
    * Call once at startup. Returns build time in ms.
    */
-  init(): number {
+  init(
+    xs: Float32Array,
+    ys: Float32Array,
+    vertexIds: Uint32Array,
+    edges: Uint32Array
+  ): number {
     const t0 = performance.now();
     const gl = this.gl;
-
+    const count = xs.length;
-    // Generate random positions as typed arrays (no object allocation)
+    const edgeCount = edges.length / 2;
-    const xs = new Float32Array(COUNT);
+    this.nodeCount = count;
-    const ys = new Float32Array(COUNT);
-    for (let i = 0; i < COUNT; i++) {
-      xs[i] = (Math.random() - 0.5) * EXTENT;
-      ys[i] = (Math.random() - 0.5) * EXTENT;
-    }
 
     // Build quadtree (spatially sorts the array)
-    const { sorted, leaves } = buildSpatialIndex(xs, ys);
+    const { sorted, leaves, order } = buildSpatialIndex(xs, ys);
     this.leaves = leaves;
+    this.sorted = sorted;
 
     // Pre-allocate arrays for render loop (zero-allocation rendering)
     this.visibleLeafIndices = new Uint32Array(leaves.length);
@@ -156,56 +213,85 @@ export class Renderer {
     gl.bufferData(gl.ARRAY_BUFFER, sorted, gl.STATIC_DRAW);
     gl.bindVertexArray(null);
 
-    // Build relationships (lines)
+    // Build vertex ID → original input index mapping
-    const lineIndices = new Uint32Array(COUNT * 4);
+    const vertexIdToOriginal = new Map<number, number>();
-    for (let j = 0; j < leaves.length; j++) {
+    for (let i = 0; i < count; i++) {
-      const lf = leaves[j];
+      vertexIdToOriginal.set(vertexIds[i], i);
-      const leafSize = lf.end - lf.start;
+    }
-      if (leafSize <= 1) continue;
 
-      for (let i = lf.start; i < lf.end; i++) {
+    // Build original input index → sorted index mapping
-        const x = sorted[i * 2];
+    // order[sortedIdx] = originalIdx, so invert it
-        const y = sorted[i * 2 + 1];
+    const originalToSorted = new Uint32Array(count);
-        
+    for (let i = 0; i < count; i++) {
-        let best1 = -1, best2 = -1;
+      originalToSorted[order[i]] = i;
-        let dist1 = Infinity, dist2 = Infinity;
+    }
-        
-        // Find closest 2 points within a small local sliding window (spatially coherent)
-        const windowSize = Math.min(12, leafSize - 1);
-        for (let w = 1; w <= windowSize; w++) {
-          const candidate = lf.start + ((i - lf.start + w) % leafSize);
-          const cx = sorted[candidate * 2];
-          const cy = sorted[candidate * 2 + 1];
-          const dx = x - cx;
-          const dy = y - cy;
-          const d2 = dx*dx + dy*dy;
-          
-          if (d2 < dist1) {
-            dist2 = dist1;
-            best2 = best1;
-            dist1 = d2;
-            best1 = candidate;
-          } else if (d2 < dist2) {
-            dist2 = d2;
-            best2 = candidate;
-          }
-        }
-        
-        // Fallback
-        if (best1 === -1) best1 = lf.start + ((i - lf.start + 1) % leafSize);
-        if (best2 === -1) best2 = lf.start + ((i - lf.start + 2) % leafSize);
 
-        const base = i * 4;
+    // Remap edges from vertex IDs to sorted indices
-        lineIndices[base + 0] = i;
+    const lineIndices = new Uint32Array(edgeCount * 2);
-        lineIndices[base + 1] = best1;
+    let validEdges = 0;
-        lineIndices[base + 2] = i;
+    for (let i = 0; i < edgeCount; i++) {
-        lineIndices[base + 3] = best2;
+      const srcId = edges[i * 2];
+      const dstId = edges[i * 2 + 1];
+      const srcOrig = vertexIdToOriginal.get(srcId);
+      const dstOrig = vertexIdToOriginal.get(dstId);
+      if (srcOrig === undefined || dstOrig === undefined) continue;
+      lineIndices[validEdges * 2] = originalToSorted[srcOrig];
+      lineIndices[validEdges * 2 + 1] = originalToSorted[dstOrig];
+      validEdges++;
+    }
+    this.edgeCount = validEdges;
+
+    // Build per-node neighbor list from edges for selection queries
+    const neighborMap = new Map<number, number[]>();
+    for (let i = 0; i < validEdges; i++) {
+      const src = lineIndices[i * 2];
+      const dst = lineIndices[i * 2 + 1];
+      if (!neighborMap.has(src)) neighborMap.set(src, []);
+      neighborMap.get(src)!.push(dst);
+      if (!neighborMap.has(dst)) neighborMap.set(dst, []);
+      neighborMap.get(dst)!.push(src);
+    }
+    this.neighborMap = neighborMap;
+
+    // Build per-leaf edge index for efficient visible-only edge drawing
+    // Find which leaf each sorted index belongs to
+    const nodeToLeaf = new Uint32Array(count);
+    for (let li = 0; li < leaves.length; li++) {
+      const lf = leaves[li];
+      for (let j = lf.start; j < lf.end; j++) {
+        nodeToLeaf[j] = li;
       }
     }
 
-    // Upload lines to GPU (NOT bound to VAO)
+    // Count edges per leaf (by source node)
+    const leafEdgeCounts = new Uint32Array(leaves.length);
+    for (let i = 0; i < validEdges; i++) {
+      leafEdgeCounts[nodeToLeaf[lineIndices[i * 2]]]++;
+    }
+
+    // Compute prefix sums for edge offsets per leaf
+    const leafEdgeOffsets = new Uint32Array(leaves.length);
+    for (let i = 1; i < leaves.length; i++) {
+      leafEdgeOffsets[i] = leafEdgeOffsets[i - 1] + leafEdgeCounts[i - 1];
+    }
+
+    // Sort edges by source leaf into a new buffer
+    const sortedEdgeIndices = new Uint32Array(validEdges * 2);
+    const leafEdgeCurrent = new Uint32Array(leaves.length);
+    for (let i = 0; i < validEdges; i++) {
+      const leafIdx = nodeToLeaf[lineIndices[i * 2]];
+      const pos = leafEdgeOffsets[leafIdx] + leafEdgeCurrent[leafIdx];
+      sortedEdgeIndices[pos * 2] = lineIndices[i * 2];
+      sortedEdgeIndices[pos * 2 + 1] = lineIndices[i * 2 + 1];
+      leafEdgeCurrent[leafIdx]++;
+    }
+
+    this.leafEdgeStarts = leafEdgeOffsets;
+    this.leafEdgeCounts = leafEdgeCounts;
+
+    // Upload sorted edges to GPU
     gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.linesIbo);
-    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, lineIndices, gl.STATIC_DRAW);
+    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, sortedEdgeIndices, gl.STATIC_DRAW);
     gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);
 
     return performance.now() - t0;
@@ -241,6 +327,135 @@ export class Renderer {
     return this.zoom;
   }
 
+  getNodeCount(): number {
+    return this.nodeCount;
+  }
+
+  /**
+   * Convert screen coordinates (CSS pixels) to world coordinates.
+   */
+  screenToWorld(screenX: number, screenY: number): { x: number; y: number } {
+    const dpr = window.devicePixelRatio || 1;
+    const px = screenX * dpr;
+    const py = screenY * dpr;
+    const wx = this.cx + (px - this.canvas.width / 2) / this.zoom;
+    const wy = this.cy + (py - this.canvas.height / 2) / this.zoom;
+    return { x: wx, y: wy };
+  }
+
+  /**
+   * Find the node closest to the given screen position.
+   * Uses the quadtree to narrow down the search.
+   * Returns the node's world coordinates if found within the visual radius, or null.
+   */
+  findNodeAt(screenX: number, screenY: number): { x: number; y: number } | null {
+    const result = this.findNodeIndexAt(screenX, screenY);
+    return result ? { x: result.x, y: result.y } : null;
+  }
+
+  /**
+   * Find the node closest to the given screen position.
+   * Returns the node's index and world coordinates if found, or null.
+   */
+  findNodeIndexAt(screenX: number, screenY: number): { index: number; x: number; y: number } | null {
+    if (this.sorted.length === 0) return null;
+
+    const world = this.screenToWorld(screenX, screenY);
+    const wx = world.x;
+    const wy = world.y;
+
+    // Calculate the search radius in world units (based on point size on screen)
+    // We use a slightly larger radius for easier hovering
+    const dpr = window.devicePixelRatio || 1;
+    const ptSizeScreen = Math.max(1.0, Math.min(this.maxPtSize, WORLD_RADIUS * 2 * this.zoom));
+    const hitRadius = (ptSizeScreen / this.zoom / dpr) * 0.75; // world units
+    const hitRadiusSq = hitRadius * hitRadius;
+
+    let closestDist = Infinity;
+    let closestIndex = -1;
+    let closestX = 0;
+    let closestY = 0;
+
+    // Traverse all leaves and check if they intersect with the hit area
+    for (let i = 0; i < this.leaves.length; i++) {
+      const lf = this.leaves[i];
+
+      // Quick AABB check: does this leaf possibly contain points near our target?
+      if (
+        wx + hitRadius < lf.minX ||
+        wx - hitRadius > lf.maxX ||
+        wy + hitRadius < lf.minY ||
+        wy - hitRadius > lf.maxY
+      ) {
+        continue; // Leaf is too far away
+      }
+
+      // Check all points in this leaf
+      for (let j = lf.start; j < lf.end; j++) {
+        const px = this.sorted[j * 2];
+        const py = this.sorted[j * 2 + 1];
+        const dx = px - wx;
+        const dy = py - wy;
+        const distSq = dx * dx + dy * dy;
+
+        if (distSq < hitRadiusSq && distSq < closestDist) {
+          closestDist = distSq;
+          closestIndex = j;
+          closestX = px;
+          closestY = py;
+        }
+      }
+    }
+
+    return closestIndex >= 0 ? { index: closestIndex, x: closestX, y: closestY } : null;
+  }
+
+  /**
+   * Update the selection buffer with the given set of node indices.
+   * Also computes neighbors of selected nodes.
+   * Call this whenever React's selection state changes.
+   */
+  updateSelection(selectedIndices: Set<number>): void {
+    const gl = this.gl;
+
+    // Upload selected indices
+    const indices = new Uint32Array(selectedIndices);
+    this.selectionCount = indices.length;
+    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.selectionIbo);
+    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.DYNAMIC_DRAW);
+    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);
+
+    // Compute neighbors of selected nodes (excluding already selected)
+    const neighborSet = new Set<number>();
+    for (const nodeIdx of selectedIndices) {
+      const nodeNeighbors = this.neighborMap.get(nodeIdx);
+      if (!nodeNeighbors) continue;
+      for (const n of nodeNeighbors) {
+        if (!selectedIndices.has(n)) {
+          neighborSet.add(n);
+        }
+      }
+    }
+
+    // Upload neighbor indices
+    const neighborIndices = new Uint32Array(neighborSet);
+    this.neighborCount = neighborIndices.length;
+    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.neighborIbo);
+    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, neighborIndices, gl.DYNAMIC_DRAW);
+    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);
+  }
+
+  /**
+   * Get the coordinates of a node by its index.
+   */
+  getNodeCoords(index: number): { x: number; y: number } | null {
+    if (index < 0 || index * 2 + 1 >= this.sorted.length) return null;
+    return {
+      x: this.sorted[index * 2],
+      y: this.sorted[index * 2 + 1],
+    };
+  }
+
   /* ── Render ───────────────────────────────────────────── */
 
   render(): RenderStats {
@@ -297,7 +512,7 @@ export class Renderer {
         lf.minY > vMaxY
       )
         continue;
-        
+
       this.visibleLeafIndices[visibleCount++] = i;
       totalVisibleParticles += (lf.end - lf.start);
     }
@@ -306,17 +521,17 @@ export class Renderer {
     const ratio = Math.min(1.0, MAX_DRAW / Math.max(1, totalVisibleParticles));
 
     let drawnCount = 0;
-    
+
     // 3. Prepare index/count arrays for drawing
     for (let i = 0; i < visibleCount; i++) {
       const leafIdx = this.visibleLeafIndices[i];
       const lf = this.leaves[leafIdx];
       const leafTotal = lf.end - lf.start;
-      
+
       // Since the leaf is randomly unordered internally, taking the first N points
       // is a perfect uniform spatial sample of this leaf.
       const drawCount = Math.max(1, Math.floor(leafTotal * ratio));
-      
+
       this.startsArray[i] = lf.start;
       this.countsArray[i] = drawCount;
       drawnCount += drawCount;
@@ -353,28 +568,52 @@ export class Renderer {
       gl.useProgram(this.lineProgram);
       gl.uniform2f(this.uCenterLine, this.cx, this.cy);
       gl.uniform2f(this.uScaleLine, (this.zoom * 2) / cw, (-this.zoom * 2) / ch);
-      
+
       gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.linesIbo);
-      
+
       for (let i = 0; i < visibleCount; i++) {
         const leafIdx = this.visibleLeafIndices[i];
-        const lf = this.leaves[leafIdx];
+        const edgeCount = this.leafEdgeCounts[leafIdx];
-        const leafTotal = lf.end - lf.start;
+        if (edgeCount === 0) continue;
-        if (leafTotal <= 1) continue;
+        // Each edge is 2 indices (1 line segment)
-        // Each node has 4 indices (2 lines)
+        // Offset is in bytes: edgeStart * 2 (indices per edge) * 4 (bytes per uint32)
-        // Offset is in bytes: start index * 4 (indices per point) * 4 (bytes per uint32)
+        const edgeStart = this.leafEdgeStarts[leafIdx];
-        gl.drawElements(gl.LINES, leafTotal * 4, gl.UNSIGNED_INT, lf.start * 16);
+        gl.drawElements(gl.LINES, edgeCount * 2, gl.UNSIGNED_INT, edgeStart * 2 * 4);
       }
-      
+
+      gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);
+    }
+
+    // 6. Draw Neighbor Nodes (yellow) - drawn before selected so selected appears on top
+    if (this.neighborCount > 0) {
+      gl.useProgram(this.neighborProgram);
+      gl.uniform2f(this.uCenterNeighbor, this.cx, this.cy);
+      gl.uniform2f(this.uScaleNeighbor, (this.zoom * 2) / cw, (-this.zoom * 2) / ch);
+      gl.uniform1f(this.uPtSizeNeighbor, ptSize);
+
+      gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.neighborIbo);
+      gl.drawElements(gl.POINTS, this.neighborCount, gl.UNSIGNED_INT, 0);
+      gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);
+    }
+
+    // 7. Draw Selected Nodes on top (orange)
+    if (this.selectionCount > 0) {
+      gl.useProgram(this.selectedProgram);
+      gl.uniform2f(this.uCenterSelected, this.cx, this.cy);
+      gl.uniform2f(this.uScaleSelected, (this.zoom * 2) / cw, (-this.zoom * 2) / ch);
+      gl.uniform1f(this.uPtSizeSelected, ptSize);
+
+      gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.selectionIbo);
+      gl.drawElements(gl.POINTS, this.selectionCount, gl.UNSIGNED_INT, 0);
       gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);
     }
 
     gl.bindVertexArray(null);
 
-    const mode = ratio === 1.0 
+    const mode = ratio === 1.0
-      ? '100% visible nodes' 
+      ? '100% visible nodes'
       : ((ratio * 100).toFixed(1) + '% of visible nodes');
-      
+
     return { drawnCount, mode, zoom: this.zoom, ptSize };
   }
 
@@ -397,10 +636,10 @@ export class Renderer {
     const prog = gl.createProgram()!;
     gl.attachShader(prog, vs);
     gl.attachShader(prog, fs);
-    
+
     // Force a_pos to location 0 before linking so both programs match VAO
     gl.bindAttribLocation(prog, 0, "a_pos");
-    
+
     gl.linkProgram(prog);
     if (!gl.getProgramParameter(prog, gl.LINK_STATUS))
       throw new Error("Link: " + gl.getProgramInfoLog(prog));