feat: Add tests for spline road mesh generation

tests/geometry/spline-road-mesh.test.ts

@@ -0,0 +1,108 @@
+import { describe, expect, it } from "vitest";
+
+import { createScenePath } from "../../src/document/paths";
+import { createTerrain } from "../../src/document/terrains";
+import { buildSplineRoadMeshData } from "../../src/geometry/spline-road-mesh";
+
+describe("spline road mesh generation", () => {
+  it("builds a continuous road strip with arc-length UVs", () => {
+    const path = createScenePath({
+      id: "path-road-mesh-straight",
+      road: {
+        enabled: true,
+        width: 2,
+        shoulderWidth: 1,
+        falloff: 0.5,
+        heightOffset: 0.1,
+        terrainConform: false,
+        materialId: null
+      },
+      points: [
+        {
+          id: "point-a",
+          position: { x: 0, y: 0, z: 0 }
+        },
+        {
+          id: "point-b",
+          position: { x: 4, y: 0, z: 0 }
+        }
+      ]
+    });
+
+    const meshData = buildSplineRoadMeshData({ path });
+
+    expect(meshData).not.toBeNull();
+    expect(meshData?.stationCount).toBe(2);
+    expect(meshData?.totalLength).toBe(4);
+    expect(Array.from(meshData!.positions)).toEqual([
+      0,
+      0.1,
+      1,
+      0,
+      0.1,
+      -1,
+      4,
+      0.1,
+      1,
+      4,
+      0.1,
+      -1
+    ]);
+    expect(Array.from(meshData!.uvs)).toEqual([0, 0, 1, 0, 0, 4, 1, 4]);
+    expect(Array.from(meshData!.indices)).toEqual([0, 1, 2, 2, 1, 3]);
+  });
+
+  it("conforms road edge vertices to terrain when enabled", () => {
+    const terrain = createTerrain({
+      id: "terrain-road-mesh-conform",
+      position: { x: 0, y: 1, z: 0 },
+      sampleCountX: 3,
+      sampleCountZ: 3,
+      cellSize: 1,
+      heights: [
+        0,
+        0,
+        0,
+        1,
+        1,
+        1,
+        2,
+        2,
+        2
+      ]
+    });
+    const path = createScenePath({
+      id: "path-road-mesh-conform",
+      road: {
+        enabled: true,
+        width: 2,
+        shoulderWidth: 0,
+        falloff: 0,
+        heightOffset: 0.25,
+        terrainConform: true,
+        materialId: null
+      },
+      points: [
+        {
+          id: "point-a",
+          position: { x: 0, y: 10, z: 1 }
+        },
+        {
+          id: "point-b",
+          position: { x: 2, y: 10, z: 1 }
+        }
+      ]
+    });
+
+    const meshData = buildSplineRoadMeshData({
+      path,
+      terrains: [terrain]
+    });
+
+    expect(meshData).not.toBeNull();
+    expect(meshData!.positions[1]).toBe(3.25);
+    expect(meshData!.positions[4]).toBe(1.25);
+    expect(meshData!.positions[7]).toBe(3.25);
+    expect(meshData!.positions[10]).toBe(1.25);
+  });
+});