GHZShaPAN/Assets/TerrainComposer2/Scripts/Terrain/TC_MultiTerrainBoost.cs

using UnityEngine;
using System.Collections;

public class TC_MultiTerrainBoost : MonoBehaviour 
{
	Camera MainCamera;
	bool[] active1;
	Terrain[] terrains;
	Bounds[] bounds;
	Plane[] planes;
	float distance;
	int count_terrain;
		
	void Start() {
		MainCamera = GetComponent<Camera>();
		terrains = Resources.FindObjectsOfTypeAll(typeof(Terrain)) as Terrain[];
		bounds = new Bounds[terrains.Length];
		active1 = new bool[terrains.Length];
		calcBounds();
	}
	
	void LateUpdate () {
		calcFrustrum();
		
		for (count_terrain = 0;count_terrain < bounds.Length;++count_terrain) {
			if (IsRenderedFrom(bounds[count_terrain])) {
				if (!active1[count_terrain]) {
					terrains[count_terrain].enabled = true;
					active1[count_terrain] = true;
				}
			}
			else {
				if (active1[count_terrain]) {
					terrains[count_terrain].enabled = false;
					active1[count_terrain] = false;
				}
			} 
		}
	}
	
	void calcBounds() {
		for (count_terrain = 0;count_terrain < terrains.Length;++count_terrain) {
			bounds[count_terrain].size = terrains[count_terrain].terrainData.size;
			bounds[count_terrain].center = new Vector3(terrains[count_terrain].transform.position.x+(bounds[count_terrain].size.x/2),terrains[count_terrain].transform.position.y+(bounds[count_terrain].size.y/2),terrains[count_terrain].transform.position.z+(bounds[count_terrain].size.z/2));
			active1[count_terrain] = true;
		}
	}
	
	void calcFrustrum()	{
		planes = GeometryUtility.CalculateFrustumPlanes(MainCamera);
	}
	
	bool IsRenderedFrom(Bounds bound) {
	    return GeometryUtility.TestPlanesAABB(planes,bound);
	}
}