auto-git:

[add] tests/geometry/terrain-brush.test.ts

tests/geometry/terrain-brush.test.ts

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+import { describe, expect, it } from "vitest";
+
+import { createDefaultTerrainBrushSettings } from "../../src/core/terrain-brush";
+import { createTerrain } from "../../src/document/terrains";
+import {
+  applyTerrainBrushStamp,
+  getTerrainBrushWeight,
+  sampleTerrainHeightAtWorldPosition
+} from "../../src/geometry/terrain-brush";
+
+describe("terrain brush geometry", () => {
+  it("samples terrain height across the regular XZ grid", () => {
+    const terrain = createTerrain({
+      id: "terrain-sample-height",
+      position: { x: 0, y: 0, z: 0 },
+      sampleCountX: 2,
+      sampleCountZ: 2,
+      cellSize: 2,
+      heights: [0, 2, 4, 6]
+    });
+
+    expect(sampleTerrainHeightAtWorldPosition(terrain, 1, 1)).toBe(3);
+  });
+
+  it("raises and lowers height samples with radial falloff", () => {
+    const terrain = createTerrain({
+      id: "terrain-sculpt",
+      position: { x: 0, y: 0, z: 0 },
+      sampleCountX: 3,
+      sampleCountZ: 3,
+      cellSize: 1,
+      heights: new Array(9).fill(0)
+    });
+    const settings = {
+      ...createDefaultTerrainBrushSettings(),
+      radius: 1.2,
+      strength: 0.5,
+      falloff: 0.5
+    };
+    const raisedTerrain = applyTerrainBrushStamp({
+      terrain,
+      center: { x: 1, z: 1 },
+      settings,
+      tool: "raise"
+    });
+    const loweredTerrain = applyTerrainBrushStamp({
+      terrain: raisedTerrain,
+      center: { x: 1, z: 1 },
+      settings,
+      tool: "lower"
+    });
+
+    expect(raisedTerrain.heights[4]).toBeCloseTo(0.5);
+    expect(raisedTerrain.heights[0]).toBe(0);
+    expect(loweredTerrain.heights[4]).toBeCloseTo(0);
+  });
+
+  it("smooths sharp spikes toward neighboring heights", () => {
+    const terrain = createTerrain({
+      id: "terrain-smooth",
+      position: { x: 0, y: 0, z: 0 },
+      sampleCountX: 3,
+      sampleCountZ: 3,
+      cellSize: 1,
+      heights: [0, 0, 0, 0, 10, 0, 0, 0, 0]
+    });
+
+    const smoothedTerrain = applyTerrainBrushStamp({
+      terrain,
+      center: { x: 1, z: 1 },
+      settings: {
+        radius: 1.5,
+        strength: 1,
+        falloff: 0
+      },
+      tool: "smooth"
+    });
+
+    expect(smoothedTerrain.heights[4]).toBeLessThan(10);
+    expect(smoothedTerrain.heights[4]).toBeCloseTo(10 / 9);
+  });
+
+  it("flattens toward the stroke-start reference height", () => {
+    const terrain = createTerrain({
+      id: "terrain-flatten",
+      position: { x: 0, y: 0, z: 0 },
+      sampleCountX: 3,
+      sampleCountZ: 3,
+      cellSize: 1,
+      heights: [0, 0, 0, 0, 4, 0, 0, 0, 0]
+    });
+
+    const flattenedTerrain = applyTerrainBrushStamp({
+      terrain,
+      center: { x: 1, z: 1 },
+      settings: {
+        radius: 1.2,
+        strength: 0.5,
+        falloff: 0
+      },
+      tool: "flatten",
+      referenceHeight: 2
+    });
+
+    expect(flattenedTerrain.heights[4]).toBeCloseTo(3);
+  });
+
+  it("returns zero influence outside the brush radius", () => {
+    expect(getTerrainBrushWeight(2, 1, 0.5)).toBe(0);
+  });
+});