fix(viewer): harden WebGPU slab recovery (#518)

Co-authored-by: Connor Soohoo <connorsoohoo@users.noreply.github.com>

packages/nodes/src/slab/__tests__/geometry.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, test } from 'bun:test'
+import { SlabNode } from '@pascal-app/core'
+import { Mesh } from 'three'
+import { buildSlabGeometry } from '../geometry'
+
+describe('buildSlabGeometry', () => {
+  test('copies the primary UVs into uv2 for every slab mesh', () => {
+    const slab = SlabNode.parse({
+      polygon: [
+        [0, 0],
+        [2, 0],
+        [2, 2],
+        [0, 2],
+      ],
+    })
+
+    const group = buildSlabGeometry(slab, undefined, 'solid', false)
+    const meshes = group.children.filter((child): child is Mesh => child instanceof Mesh)
+
+    expect(meshes).toHaveLength(2)
+    for (const mesh of meshes) {
+      const uv = mesh.geometry.getAttribute('uv')
+      const uv2 = mesh.geometry.getAttribute('uv2')
+
+      expect(uv2).toBeDefined()
+      expect(uv2.itemSize).toBe(2)
+      expect(uv2.count).toBe(uv.count)
+      expect(Array.from(uv2.array)).toEqual(Array.from(uv.array))
+    }
+  })
+})

packages/nodes/src/slab/geometry.ts

@@ -127,7 +127,10 @@ function splitSlabFacesByFacing(geometry: BufferGeometry): {
   const build = (data: { pos: number[]; uv: number[] }) => {
     const geo = new BufferGeometry()
     geo.setAttribute('position', new Float32BufferAttribute(data.pos, 3))
-    if (data.uv.length > 0) geo.setAttribute('uv', new Float32BufferAttribute(data.uv, 2))
+    if (data.uv.length > 0) {
+      geo.setAttribute('uv', new Float32BufferAttribute(data.uv, 2))
+      geo.setAttribute('uv2', new Float32BufferAttribute(data.uv.slice(), 2))
+    }
     geo.computeVertexNormals()
     return geo
   }