Implement support for clipping road mesh geometry using visible station runs

src/geometry/spline-road-mesh.ts

@@ -415,6 +415,7 @@ function addEdgeProfileCaps(options: {
 export function buildSplineRoadMeshData(options: {
   path: SplineRoadPathLike;
   terrains?: readonly Terrain[];
+  clipIntervals?: readonly SplineCorridorPathClipInterval[];
 }): SplineRoadMeshData | null {
   const { path } = options;
   const terrains = options.terrains ?? [];
@@ -428,10 +429,18 @@ export function buildSplineRoadMeshData(options: {
   const uvs: number[] = [];
   const indices: number[] = [];
   const halfWidth = path.road.width * 0.5;
+  const stationRuns = buildVisibleRoadStationRuns(
+    stations,
+    options.clipIntervals ?? []
+  );
+  let stationCount = 0;
 
-  for (let index = 0; index < stations.length; index += 1) {
-    const station = stations[index]!;
-    const tangent = resolveStationTangent(stations, index);
+  for (const run of stationRuns) {
+    const runVertexOffset = positions.length / 3;
+
+    for (let index = 0; index < run.length; index += 1) {
+      const station = run[index]!;
+      const tangent = resolveStationTangent(run, index);
 
       if (tangent === null) {
         return null;
@@ -459,8 +468,8 @@ export function buildSplineRoadMeshData(options: {
       uvs.push(0, station.distance, 1, station.distance);
     }
 
-  for (let index = 0; index < stations.length - 1; index += 1) {
-    const left = index * 2;
+    for (let index = 0; index < run.length - 1; index += 1) {
+      const left = runVertexOffset + index * 2;
       const right = left + 1;
       const nextLeft = left + 2;
       const nextRight = left + 3;
@@ -468,12 +477,19 @@ export function buildSplineRoadMeshData(options: {
       indices.push(left, right, nextLeft, nextLeft, right, nextRight);
     }
 
+    stationCount += run.length;
+  }
+
+  if (positions.length === 0) {
+    return null;
+  }
+
   return {
     pathId: path.id,
     positions: new Float32Array(positions),
     uvs: new Float32Array(uvs),
     indices: new Uint32Array(indices),
-    stationCount: stations.length,
+    stationCount,
     totalLength: stations[stations.length - 1]?.distance ?? 0
   };
 }
@@ -481,6 +497,7 @@ export function buildSplineRoadMeshData(options: {
 export function buildSplineRoadMeshGeometry(options: {
   path: SplineRoadPathLike;
   terrains?: readonly Terrain[];
+  clipIntervals?: readonly SplineCorridorPathClipInterval[];
 }): BufferGeometry | null {
   const meshData = buildSplineRoadMeshData(options);