diff --git a/src/viewport-three/viewport-host.ts b/src/viewport-three/viewport-host.ts
new file mode 100644
index 00000000..1f8c91a5
--- /dev/null
+++ b/src/viewport-three/viewport-host.ts
@@ -0,0 +1,384 @@
+import {
+  AmbientLight,
+  AxesHelper,
+  BoxGeometry,
+  CanvasTexture,
+  Color,
+  DirectionalLight,
+  EdgesGeometry,
+  GridHelper,
+  Group,
+  LineBasicMaterial,
+  LineSegments,
+  Mesh,
+  MeshStandardMaterial,
+  PerspectiveCamera,
+  Raycaster,
+  RepeatWrapping,
+  Scene,
+  SRGBColorSpace,
+  Vector2,
+  Vector3,
+  WebGLRenderer
+} from "three";
+
+import { isBrushFaceSelected, isBrushSelected, type EditorSelection } from "../core/selection";
+import type { SceneDocument, WorldSettings } from "../document/scene-document";
+import { BOX_FACE_IDS, type BoxBrush, type BoxFaceId } from "../document/brushes";
+import { applyBoxBrushFaceUvsToGeometry } from "../geometry/box-face-uvs";
+import type { MaterialDef } from "../materials/starter-material-library";
+
+interface BrushRenderObjects {
+  mesh: Mesh<BoxGeometry, MeshStandardMaterial[]>;
+  edges: LineSegments<EdgesGeometry, LineBasicMaterial>;
+}
+
+interface CachedMaterialTexture {
+  signature: string;
+  texture: CanvasTexture;
+}
+
+const BRUSH_BASE_COLOR = 0x8c98a7;
+const BRUSH_SELECTED_EDGE_COLOR = 0xf7d2aa;
+const BRUSH_EDGE_COLOR = 0x0d1017;
+const FALLBACK_FACE_COLOR = 0x747d89;
+const SELECTED_FACE_FALLBACK_COLOR = 0xcf7b42;
+const SELECTED_FACE_EMISSIVE = 0x4a2814;
+
+function createMaterialSignature(material: MaterialDef): string {
+  return `${material.baseColorHex}|${material.accentColorHex}|${material.pattern}`;
+}
+
+function fillMaterialPattern(context: CanvasRenderingContext2D, material: MaterialDef, size: number) {
+  context.fillStyle = material.baseColorHex;
+  context.fillRect(0, 0, size, size);
+  context.strokeStyle = material.accentColorHex;
+  context.fillStyle = material.accentColorHex;
+
+  switch (material.pattern) {
+    case "grid":
+      context.lineWidth = Math.max(2, size / 32);
+
+      for (let offset = 0; offset <= size; offset += size / 4) {
+        context.beginPath();
+        context.moveTo(offset, 0);
+        context.lineTo(offset, size);
+        context.stroke();
+
+        context.beginPath();
+        context.moveTo(0, offset);
+        context.lineTo(size, offset);
+        context.stroke();
+      }
+      break;
+    case "checker": {
+      const checkerSize = size / 4;
+
+      for (let row = 0; row < 4; row += 1) {
+        for (let column = 0; column < 4; column += 1) {
+          if ((row + column) % 2 === 0) {
+            context.fillRect(column * checkerSize, row * checkerSize, checkerSize, checkerSize);
+          }
+        }
+      }
+      break;
+    }
+    case "stripes":
+      context.lineWidth = size / 6;
+
+      for (let offset = -size; offset <= size * 2; offset += size / 3) {
+        context.beginPath();
+        context.moveTo(offset, size);
+        context.lineTo(offset + size, 0);
+        context.stroke();
+      }
+      break;
+    case "diamond":
+      context.lineWidth = Math.max(2, size / 28);
+
+      for (let offset = -size; offset <= size; offset += size / 3) {
+        context.beginPath();
+        context.moveTo(size * 0.5, offset);
+        context.lineTo(size - offset, size * 0.5);
+        context.lineTo(size * 0.5, size - offset);
+        context.lineTo(-offset, size * 0.5);
+        context.closePath();
+        context.stroke();
+      }
+      break;
+  }
+}
+
+export class ViewportHost {
+  private readonly scene = new Scene();
+  private readonly camera = new PerspectiveCamera(60, 1, 0.1, 1000);
+  private readonly renderer = new WebGLRenderer({ antialias: true });
+  private readonly ambientLight = new AmbientLight();
+  private readonly sunLight = new DirectionalLight();
+  private readonly brushGroup = new Group();
+  private readonly raycaster = new Raycaster();
+  private readonly pointer = new Vector2();
+  private readonly brushRenderObjects = new Map<string, BrushRenderObjects>();
+  private readonly materialTextureCache = new Map<string, CachedMaterialTexture>();
+  private resizeObserver: ResizeObserver | null = null;
+  private animationFrame = 0;
+  private container: HTMLElement | null = null;
+  private brushSelectionChangeHandler: ((selection: EditorSelection) => void) | null = null;
+
+  constructor() {
+    this.camera.position.set(10, 9, 10);
+    this.camera.lookAt(new Vector3(0, 0, 0));
+
+    const gridHelper = new GridHelper(40, 40, 0xcf8354, 0x4e596b);
+    const axesHelper = new AxesHelper(2);
+
+    this.scene.add(gridHelper);
+    this.scene.add(axesHelper);
+    this.scene.add(this.ambientLight);
+    this.scene.add(this.sunLight);
+    this.scene.add(this.brushGroup);
+    this.renderer.setPixelRatio(Math.min(window.devicePixelRatio, 2));
+  }
+
+  mount(container: HTMLElement) {
+    this.container = container;
+    container.appendChild(this.renderer.domElement);
+    this.renderer.domElement.addEventListener("pointerdown", this.handlePointerDown);
+    this.resize();
+
+    this.resizeObserver = new ResizeObserver(() => {
+      this.resize();
+    });
+    this.resizeObserver.observe(container);
+
+    this.render();
+  }
+
+  updateWorld(world: WorldSettings) {
+    this.scene.background = new Color(world.background.colorHex);
+    this.ambientLight.color.set(world.ambientLight.colorHex);
+    this.ambientLight.intensity = world.ambientLight.intensity;
+    this.sunLight.color.set(world.sunLight.colorHex);
+    this.sunLight.intensity = world.sunLight.intensity;
+    this.sunLight.position.set(world.sunLight.direction.x, world.sunLight.direction.y, world.sunLight.direction.z).normalize().multiplyScalar(18);
+  }
+
+  updateDocument(document: SceneDocument, selection: EditorSelection) {
+    this.rebuildBrushMeshes(document, selection);
+  }
+
+  setBrushSelectionChangeHandler(handler: ((selection: EditorSelection) => void) | null) {
+    this.brushSelectionChangeHandler = handler;
+  }
+
+  dispose() {
+    if (this.animationFrame !== 0) {
+      cancelAnimationFrame(this.animationFrame);
+      this.animationFrame = 0;
+    }
+
+    this.resizeObserver?.disconnect();
+    this.resizeObserver = null;
+    this.renderer.domElement.removeEventListener("pointerdown", this.handlePointerDown);
+    this.clearBrushMeshes();
+
+    for (const cachedTexture of this.materialTextureCache.values()) {
+      cachedTexture.texture.dispose();
+    }
+
+    this.materialTextureCache.clear();
+    this.renderer.dispose();
+
+    if (this.container !== null && this.container.contains(this.renderer.domElement)) {
+      this.container.removeChild(this.renderer.domElement);
+    }
+
+    this.container = null;
+  }
+
+  private rebuildBrushMeshes(document: SceneDocument, selection: EditorSelection) {
+    this.clearBrushMeshes();
+
+    for (const brush of Object.values(document.brushes)) {
+      const geometry = new BoxGeometry(brush.size.x, brush.size.y, brush.size.z);
+      applyBoxBrushFaceUvsToGeometry(geometry, brush);
+
+      const materials = BOX_FACE_IDS.map((faceId) =>
+        this.createFaceMaterial(
+          brush,
+          faceId,
+          document.materials[brush.faces[faceId].materialId ?? ""],
+          isBrushFaceSelected(selection, brush.id, faceId)
+        )
+      );
+      const mesh = new Mesh(geometry, materials);
+      const brushSelected = isBrushSelected(selection, brush.id);
+
+      mesh.position.set(brush.center.x, brush.center.y, brush.center.z);
+      mesh.userData.brushId = brush.id;
+      mesh.castShadow = false;
+      mesh.receiveShadow = false;
+
+      const edges = new LineSegments(
+        new EdgesGeometry(geometry),
+        new LineBasicMaterial({
+          color: brushSelected ? BRUSH_SELECTED_EDGE_COLOR : BRUSH_EDGE_COLOR
+        })
+      );
+      edges.position.copy(mesh.position);
+
+      this.brushGroup.add(mesh);
+      this.brushGroup.add(edges);
+      this.brushRenderObjects.set(brush.id, {
+        mesh,
+        edges
+      });
+    }
+  }
+
+  private createFaceMaterial(brush: BoxBrush, faceId: BoxFaceId, material: MaterialDef | undefined, selectedFace: boolean): MeshStandardMaterial {
+    const face = brush.faces[faceId];
+
+    if (material === undefined || face.materialId === null) {
+      return new MeshStandardMaterial({
+        color: selectedFace ? SELECTED_FACE_FALLBACK_COLOR : FALLBACK_FACE_COLOR,
+        emissive: selectedFace ? SELECTED_FACE_EMISSIVE : 0x000000,
+        emissiveIntensity: selectedFace ? 0.28 : 0,
+        roughness: 0.9,
+        metalness: 0.05
+      });
+    }
+
+    return new MeshStandardMaterial({
+      color: 0xffffff,
+      map: this.getOrCreateTexture(material),
+      emissive: selectedFace ? SELECTED_FACE_EMISSIVE : 0x000000,
+      emissiveIntensity: selectedFace ? 0.32 : 0,
+      roughness: 0.92,
+      metalness: 0.02
+    });
+  }
+
+  private getOrCreateTexture(material: MaterialDef): CanvasTexture {
+    const signature = createMaterialSignature(material);
+    const cachedTexture = this.materialTextureCache.get(material.id);
+
+    if (cachedTexture !== undefined && cachedTexture.signature === signature) {
+      return cachedTexture.texture;
+    }
+
+    cachedTexture?.texture.dispose();
+
+    const canvas = document.createElement("canvas");
+    canvas.width = 128;
+    canvas.height = 128;
+
+    const context = canvas.getContext("2d");
+
+    if (context === null) {
+      throw new Error("2D canvas context is unavailable for starter material texture generation.");
+    }
+
+    fillMaterialPattern(context, material, canvas.width);
+
+    const texture = new CanvasTexture(canvas);
+    texture.wrapS = RepeatWrapping;
+    texture.wrapT = RepeatWrapping;
+    texture.colorSpace = SRGBColorSpace;
+    texture.needsUpdate = true;
+
+    this.materialTextureCache.set(material.id, {
+      signature,
+      texture
+    });
+
+    return texture;
+  }
+
+  private clearBrushMeshes() {
+    for (const renderObjects of this.brushRenderObjects.values()) {
+      this.brushGroup.remove(renderObjects.mesh);
+      this.brushGroup.remove(renderObjects.edges);
+      renderObjects.mesh.geometry.dispose();
+
+      for (const material of renderObjects.mesh.material) {
+        material.dispose();
+      }
+
+      renderObjects.edges.geometry.dispose();
+      renderObjects.edges.material.dispose();
+    }
+
+    this.brushRenderObjects.clear();
+  }
+
+  private resize() {
+    if (this.container === null) {
+      return;
+    }
+
+    const width = this.container.clientWidth;
+    const height = this.container.clientHeight;
+
+    if (width === 0 || height === 0) {
+      return;
+    }
+
+    this.camera.aspect = width / height;
+    this.camera.updateProjectionMatrix();
+    this.renderer.setSize(width, height, false);
+  }
+
+  private handlePointerDown = (event: PointerEvent) => {
+    const bounds = this.renderer.domElement.getBoundingClientRect();
+
+    if (bounds.width === 0 || bounds.height === 0) {
+      return;
+    }
+
+    this.pointer.x = ((event.clientX - bounds.left) / bounds.width) * 2 - 1;
+    this.pointer.y = -(((event.clientY - bounds.top) / bounds.height) * 2 - 1);
+
+    this.raycaster.setFromCamera(this.pointer, this.camera);
+
+    const hits = this.raycaster.intersectObjects(
+      Array.from(this.brushRenderObjects.values(), (renderObjects) => renderObjects.mesh),
+      false
+    );
+
+    if (hits.length === 0) {
+      this.brushSelectionChangeHandler?.({
+        kind: "none"
+      });
+      return;
+    }
+
+    const hit = hits[0];
+    const brushId = hit.object.userData.brushId;
+    const faceMaterialIndex = hit.face?.materialIndex;
+    const faceId = typeof faceMaterialIndex === "number" ? BOX_FACE_IDS[faceMaterialIndex] ?? null : null;
+
+    if (typeof brushId !== "string") {
+      return;
+    }
+
+    if (faceId !== null) {
+      this.brushSelectionChangeHandler?.({
+        kind: "brushFace",
+        brushId,
+        faceId
+      });
+      return;
+    }
+
+    this.brushSelectionChangeHandler?.({
+      kind: "brushes",
+      ids: [brushId]
+    });
+  };
+
+  private render = () => {
+    this.animationFrame = window.requestAnimationFrame(this.render);
+    this.renderer.render(this.scene, this.camera);
+  };
+}