Add paint hover previews to viewer

packages/viewer/src/systems/stair/stair-materials.ts

@@ -12,6 +12,18 @@ import {
 
 export type StairBodyMaterials = [THREE.Material, THREE.Material]
 
+const stairBodyMaterialCache = new Map<string, StairBodyMaterials>()
+const stairRailingMaterialCache = new Map<string, THREE.Material>()
+
+function getSurfaceMaterialSignature(
+  spec: ReturnType<typeof getEffectiveStairSurfaceMaterial>,
+): string {
+  return JSON.stringify({
+    material: spec.material ?? null,
+    materialPreset: spec.materialPreset ?? null,
+  })
+}
+
 function createResolvedMaterial(
   material: StairNode['material'] | StairSegmentNode['material'] | undefined,
   materialPreset: string | undefined,
@@ -30,16 +42,32 @@ function createResolvedMaterial(
 export function getStairBodyMaterials(stair: StairNode): StairBodyMaterials {
   const tread = getEffectiveStairSurfaceMaterial(stair, 'tread')
   const side = getEffectiveStairSurfaceMaterial(stair, 'side')
+  const cacheKey = JSON.stringify({
+    tread: getSurfaceMaterialSignature(tread),
+    side: getSurfaceMaterialSignature(side),
+  })
 
-  return [
+  const cached = stairBodyMaterialCache.get(cacheKey)
+  if (cached) return cached
+
+  const materials: StairBodyMaterials = [
     createResolvedMaterial(tread.material, tread.materialPreset),
     createResolvedMaterial(side.material, side.materialPreset),
   ]
+
+  stairBodyMaterialCache.set(cacheKey, materials)
+  return materials
 }
 
 export function getStairRailingMaterial(stair: StairNode): THREE.Material {
   const railing = getEffectiveStairSurfaceMaterial(stair, 'railing')
-  return createResolvedMaterial(railing.material, railing.materialPreset)
+  const cacheKey = getSurfaceMaterialSignature(railing)
+  const cached = stairRailingMaterialCache.get(cacheKey)
+  if (cached) return cached
+
+  const material = createResolvedMaterial(railing.material, railing.materialPreset)
+  stairRailingMaterialCache.set(cacheKey, material)
+  return material
 }
 
 export function getStraightStairSegmentBodyMaterials(