Add unit tests for terrain LOD mesh generation and level resolution

tests/geometry/terrain-mesh.test.ts

@@ -1,7 +1,11 @@
 import { describe, expect, it } from "vitest";
 
 import { createTerrain } from "../../src/document/terrains";
-import { buildTerrainDerivedMeshData } from "../../src/geometry/terrain-mesh";
+import {
+  buildTerrainDerivedMeshData,
+  buildTerrainLodMeshData,
+  resolveTerrainLodLevelIndex
+} from "../../src/geometry/terrain-mesh";
 
 describe("terrain mesh generation", () => {
   it("chooses the forward diagonal when the opposite-corner height delta is smaller", () => {
@@ -98,4 +102,147 @@ describe("terrain mesh generation", () => {
       expect.closeTo(0.25, 5)
     ]);
   });
+
+  it("chunks terrain LoD data across non-multiple-of-64 terrain edges", () => {
+    const terrain = createTerrain({
+      sampleCountX: 130,
+      sampleCountZ: 70
+    });
+
+    const lodMesh = buildTerrainLodMeshData(terrain);
+
+    expect(lodMesh.chunks).toHaveLength(6);
+    expect(lodMesh.chunks[0]).toMatchObject({
+      chunkX: 0,
+      chunkZ: 0,
+      startSampleX: 0,
+      startSampleZ: 0,
+      endSampleX: 64,
+      endSampleZ: 64
+    });
+    expect(lodMesh.chunks.at(-1)).toMatchObject({
+      chunkX: 2,
+      chunkZ: 1,
+      startSampleX: 128,
+      startSampleZ: 64,
+      endSampleX: 129,
+      endSampleZ: 69
+    });
+  });
+
+  it("generates smaller terrain LoD levels as stride increases", () => {
+    const terrain = createTerrain({
+      sampleCountX: 65,
+      sampleCountZ: 65
+    });
+
+    const [chunk] = buildTerrainLodMeshData(terrain).chunks;
+
+    expect(chunk).toBeDefined();
+    expect(chunk!.levels.map((level) => level.stride)).toEqual([
+      1,
+      2,
+      4,
+      8,
+      16
+    ]);
+
+    const vertexCounts = chunk!.levels.map(
+      (level) => level.positions.length / 3
+    );
+
+    for (let index = 1; index < vertexCounts.length; index += 1) {
+      expect(vertexCounts[index]).toBeLessThan(vertexCounts[index - 1]!);
+    }
+  });
+
+  it("keeps terrain LoD chunk bounds covering source heights", () => {
+    const heights = new Array(17 * 17).fill(0);
+    heights[8 * 17 + 8] = 12;
+    heights[16 * 17 + 16] = -4;
+    const terrain = createTerrain({
+      sampleCountX: 17,
+      sampleCountZ: 17,
+      heights
+    });
+
+    const [chunk] = buildTerrainLodMeshData(terrain).chunks;
+
+    expect(chunk!.localBounds.min.y).toBeLessThanOrEqual(-4);
+    expect(chunk!.localBounds.max.y).toBeGreaterThanOrEqual(12);
+  });
+
+  it("keeps terrain LoD layer weights normalized for render blending", () => {
+    const terrain = createTerrain({
+      sampleCountX: 5,
+      sampleCountZ: 5,
+      paintWeights: Array.from({ length: 5 * 5 * 3 }, (_, index) =>
+        index % 3 === 0 ? 0.2 : index % 3 === 1 ? 0.3 : 0.1
+      )
+    });
+
+    const [chunk] = buildTerrainLodMeshData(terrain).chunks;
+    const [level] = chunk!.levels;
+
+    for (
+      let offset = 0;
+      offset < level!.layerWeights.length;
+      offset += 4
+    ) {
+      const sum =
+        level!.layerWeights[offset]! +
+        level!.layerWeights[offset + 1]! +
+        level!.layerWeights[offset + 2]! +
+        level!.layerWeights[offset + 3]!;
+
+      expect(sum).toBeCloseTo(1, 5);
+    }
+  });
+
+  it("adds terrain LoD skirt vertices to hide hard-switch edge cracks", () => {
+    const terrain = createTerrain({
+      sampleCountX: 9,
+      sampleCountZ: 9
+    });
+
+    const [chunk] = buildTerrainLodMeshData(terrain).chunks;
+    const [level] = chunk!.levels;
+
+    expect(level!.skirtVertexCount).toBeGreaterThan(0);
+    expect(level!.positions.length / 3).toBeGreaterThan(9 * 9);
+  });
+
+  it("selects coarser terrain LoD levels as perspective distance increases", () => {
+    const levelCount = 5;
+    const chunkDiagonal = 100;
+    const chunkWorldCenter = { x: 0, y: 0, z: 0 };
+
+    expect(
+      resolveTerrainLodLevelIndex({
+        levelCount,
+        chunkDiagonal,
+        chunkWorldCenter,
+        cameraPosition: { x: 0, y: 0, z: 150 },
+        perspective: true
+      })
+    ).toBe(0);
+    expect(
+      resolveTerrainLodLevelIndex({
+        levelCount,
+        chunkDiagonal,
+        chunkWorldCenter,
+        cameraPosition: { x: 0, y: 0, z: 900 },
+        perspective: true
+      })
+    ).toBe(3);
+    expect(
+      resolveTerrainLodLevelIndex({
+        levelCount,
+        chunkDiagonal,
+        chunkWorldCenter,
+        cameraPosition: { x: 0, y: 0, z: 2000 },
+        perspective: true
+      })
+    ).toBe(4);
+  });
 });