UnityEngine.TerrainData.GetSteepness C# (CSharp) Method

        public extern float GetSteepness(float x, float y);
        /// <summary>

 public static void MassPlaceTrees(TerrainData terrainData, int numberOfTrees, bool randomTreeColor, bool keepExistingTrees)
 {
     int length = terrainData.treePrototypes.Length;
     if (length == 0)
     {
         Debug.Log("Can't place trees because no prototypes are defined");
     }
     else
     {
         Undo.RegisterCompleteObjectUndo(terrainData, "Mass Place Trees");
         TreeInstance[] sourceArray = new TreeInstance[numberOfTrees];
         int num2 = 0;
         while (num2 < sourceArray.Length)
         {
             TreeInstance instance = new TreeInstance {
                 position = new Vector3(UnityEngine.Random.value, 0f, UnityEngine.Random.value)
             };
             if (terrainData.GetSteepness(instance.position.x, instance.position.z) < 30f)
             {
                 instance.color = !randomTreeColor ? Color.white : GetTreeColor();
                 instance.lightmapColor = Color.white;
                 instance.prototypeIndex = UnityEngine.Random.Range(0, length);
                 instance.heightScale = GetTreeHeight();
                 instance.widthScale = !lockWidthToHeight ? GetTreeWidth() : instance.heightScale;
                 instance.rotation = GetTreeRotation();
                 sourceArray[num2++] = instance;
             }
         }
         if (keepExistingTrees)
         {
             TreeInstance[] treeInstances = terrainData.treeInstances;
             TreeInstance[] destinationArray = new TreeInstance[treeInstances.Length + sourceArray.Length];
             Array.Copy(treeInstances, 0, destinationArray, 0, treeInstances.Length);
             Array.Copy(sourceArray, 0, destinationArray, treeInstances.Length, sourceArray.Length);
             sourceArray = destinationArray;
         }
         terrainData.treeInstances = sourceArray;
         terrainData.RecalculateTreePositions();
     }
 }