Object2Terrain.js

@MenuItem ("Terrain/Object to Terrain")

static function Object2Terrain () {
	// See if a valid object is selected
	var obj = Selection.activeObject as GameObject;
	if (obj == null) { 
		EditorUtility.DisplayDialog("No object selected", "Please select an object.", "Cancel");
		return;
	}
	if (obj.GetComponent(MeshFilter) == null) {
		EditorUtility.DisplayDialog("No mesh selected", "Please select an object with a mesh.", "Cancel");
		return;
	}
	else if ((obj.GetComponent(MeshFilter) as MeshFilter).sharedMesh == null) {
		EditorUtility.DisplayDialog("No mesh selected", "Please select an object with a valid mesh.", "Cancel");
		return;		
	}
	if (Terrain.activeTerrain == null) {
		EditorUtility.DisplayDialog("No terrain found", "Please make sure a terrain exists.", "Cancel");
		return;
	}	
	var terrain = Terrain.activeTerrain.terrainData;
	
	// If there's no mesh collider, add one (and then remove it later when done)
	var addedCollider = false;
	var addedMesh = false;
	var objCollider = obj.collider as MeshCollider;
	if (objCollider == null) {
		objCollider = obj.AddComponent(MeshCollider);
		addedCollider = true;
	}
	else if (objCollider.sharedMesh == null) {
		objCollider.sharedMesh = (obj.GetComponent(MeshFilter) as MeshFilter).sharedMesh;
		addedMesh = true;
	}
	
	Undo.RegisterUndo (terrain, "Object to Terrain");

	var resolutionX = terrain.heightmapWidth;
	var resolutionZ = terrain.heightmapHeight;
	var heights = terrain.GetHeights(0, 0, resolutionX, resolutionZ);
	
	// Use bounds a bit smaller than the actual object; otherwise raycasting tends to miss at the edges
	var objectBounds = objCollider.bounds;
	var leftEdge = objectBounds.center.x - objectBounds.extents.x + .01;
	var bottomEdge = objectBounds.center.z - objectBounds.extents.z + .01;
	var stepX = (objectBounds.size.x - .019) / resolutionX;
	var stepZ = (objectBounds.size.z - .019) / resolutionZ;
	
	// Set up raycast vars
	var y = objectBounds.center.y + objectBounds.extents.y + .01;
	var hit : RaycastHit;
	var ray = new Ray(Vector3.zero, -Vector3.up);
	var rayDistance = objectBounds.size.y + .02;
	var heightFactor = 1.0 / rayDistance;
		
	// Do raycasting samples over the object to see what terrain heights should be
	var z = bottomEdge;
	for (zCount = 0; zCount < resolutionZ; zCount++) {
		var x = leftEdge;
		for (xCount = 0; xCount < resolutionX; xCount++) {
			ray.origin = Vector3(x, y, z);
			if (objCollider.Raycast(ray, hit, rayDistance)) {
				heights[zCount, xCount] = 1.0 - (y - hit.point.y)*heightFactor;
			}
			else {
				heights[zCount, xCount] = 0.0;
			}
			x += stepX;
		}
		z += stepZ;
	}
	
	terrain.SetHeights(0, 0, heights);
	
	if (addedMesh) {
		objCollider.sharedMesh = null;
	}
	if (addedCollider) {
		DestroyImmediate(objCollider);
	}
}