What is Terrain Neighbor for?

I'm trying to set terrain height via script:

But as you can see, the terrain edge isn't connected when I set height. I thought Terrain neighbor would help me solve this problem, I use this code to set neighbor

Code (CSharp):

1. void SetNeighbour(Terrain terrain, Terrain[] neighbours)
2.     {
3.         terrain.SetNeighbors(neighbours[(int)E_DIRECTION.WEST],
4.             neighbours[(int)E_DIRECTION.NORTH],
5.             neighbours[(int)E_DIRECTION.EAST],
6.             neighbours[(int)E_DIRECTION.SOUTH]);
7.         terrain.Flush();
8.  
9.         neighbours[(int)E_DIRECTION.WEST].SetNeighbors(null, null, terrain, null);
10.         neighbours[(int)E_DIRECTION.NORTH].SetNeighbors(null, null, null, terrain);
11.         neighbours[(int)E_DIRECTION.EAST].SetNeighbors(terrain, null, null, null);
12.         neighbours[(int)E_DIRECTION.SOUTH].SetNeighbors(null, terrain, null, null);
13.         foreach (var item in neighbours)
14.         {
15.             item.Flush();
16.         }
17.     }

but it doesn't solve the problem, I see terrain neighbor does nothing. I guess I have to manually sew these terrain edge then. But I'm curious: what is Terrain Neighbor for?

 

I'm going out on a limb here with an educated guess. If you have a large terrain, you don't want to keep all the terrain in memory at the same time to be processed. So, you load only the terrain neighbours that you want to be processed at any given time to save on cpu/memory.

This explains some other uses for them also.

https://blogs.unity3d.com/2018/10/10/2018-3-terrain-update-getting-started/

Sorry i can't help with your problem, I haven't used them myself yet.

 

You shouldn't use terrain.SetHeights() if you want to set heights for neighbouring terrains. Use TerrainPaintUtility.BeginPaintHeightmap() and TerrainPaintUtility.EndPaintHeightmap() methods.

 

I'm on Unity 5.6. Could you let me know how terrain neighbours are implemented in this version? This seems to be a very poorly documented area. Is there a guide to how to tile terrains properly for different versions?

 

Hi, I have a related issue. I'm trying to connect terrains with code, but I can't get it to work. The heights on each terrain on its own is correct, I just need to connect them.

What it looks like:


This is at the point where three terrains meet. You can see there's just a gap. I want the gap to be closed. I tried just nudging their positions a bit, but that doesn't solve it as textures and lighting still is disconnected.

I've tried a lot of different code, including swapping right, left, bottom and top to assure I didn't have those wrong, as well as calling "terrain.flush()" and the static "Terrain.SetConnectivityDirty()" in different orders. Autoconnect is true for all terrains, and their groupingId is 0. Below is my current code.

I call my terrain GameObjects chunks. This is the code I use to create a new chunk:

Code (CSharp):

1. TerrainData terrainData = Instantiate(defaultTerrainData);
2.             GameObject chunk = Terrain.CreateTerrainGameObject(terrainData);
3.             chunkDictionary[GetChunkKey(chunkX, chunkY)] = chunk;
4.             Terrain terrain = chunk.GetComponent<Terrain>();
5.             activeChunksCount++;
6.  
7.             UpdateChunkNeighbors(chunkX, chunkY);
8.  
9.             chunk.transform.position = new Vector3(chunkX * chunkSize.x, 0f, chunkY * chunkSize.y);

where defaultTerrainData is a terrainData object from the assets.

This is the code I use for updating the chunk neighbors. There's a lot of debug code there at the moment.

Code (CSharp):

1. private void UpdateChunkNeighbors(long chunkX, long chunkY)
2.     {
3.         GameObject chunk = GetChunk(chunkX, chunkY);
4.  
5.         if (chunk == null)
6.         {
7.             Debug.LogError("Chunk is null");
8.         }
9.  
10.         Terrain terrain = chunk.GetComponent<Terrain>();
11.  
12.         Debug.Log("terrain.rightNeighbor old: " + terrain.rightNeighbor);
13.         Debug.Log("terrain.leftNeighbor old: " + terrain.leftNeighbor);
14.         Debug.Log("terrain.topNeighbor old: " + terrain.topNeighbor);
15.         Debug.Log("terrain.bottomNeighbor old: " + terrain.bottomNeighbor);
16.  
17.         GameObject rightChunk = GetChunk(chunkX + 1, chunkY);
18.         GameObject leftChunk = GetChunk(chunkX - 1, chunkY);
19.         GameObject topChunk = GetChunk(chunkX, chunkY + 1);
20.         GameObject bottomChunk = GetChunk(chunkX, chunkY - 1);
21.  
22.         if (rightChunk != null)
23.         {
24.             Terrain terrain1 = rightChunk.GetComponent<Terrain>();
25.             terrain.SetNeighbors(terrain.leftNeighbor, terrain.topNeighbor, terrain1, terrain.bottomNeighbor);
26.             terrain1.SetNeighbors(terrain, terrain1.topNeighbor, terrain1.rightNeighbor, terrain1.bottomNeighbor);
27.             Terrain.SetConnectivityDirty();
28.             terrain.Flush();
29.             terrain1.Flush();
30.         }
31.  
32.         if (leftChunk != null)
33.         {
34.             Terrain terrain1 = leftChunk.GetComponent<Terrain>();
35.             terrain.SetNeighbors(terrain1, terrain.topNeighbor, terrain.rightNeighbor, terrain.bottomNeighbor);
36.             terrain1.SetNeighbors(terrain1.leftNeighbor, terrain1.topNeighbor, terrain, terrain1.bottomNeighbor);
37.             Terrain.SetConnectivityDirty();
38.             terrain.Flush();
39.             terrain1.Flush();
40.         }
41.  
42.         if (topChunk != null)
43.         {
44.             Terrain terrain1 = topChunk.GetComponent<Terrain>();
45.             terrain.SetNeighbors(terrain.leftNeighbor, terrain1, terrain.rightNeighbor, terrain.bottomNeighbor);
46.             terrain1.SetNeighbors(terrain1.leftNeighbor, terrain1.topNeighbor, terrain1.rightNeighbor, terrain);
47.             Terrain.SetConnectivityDirty();
48.             terrain.Flush();
49.             terrain1.Flush();
50.         }
51.  
52.         if (bottomChunk != null)
53.         {
54.             Terrain terrain1 = bottomChunk.GetComponent<Terrain>();
55.             terrain.SetNeighbors(terrain.leftNeighbor, terrain.topNeighbor, terrain.rightNeighbor, terrain1);
56.             terrain1.SetNeighbors(terrain1.leftNeighbor, terrain, terrain1.rightNeighbor, terrain1.bottomNeighbor);
57.             Terrain.SetConnectivityDirty();
58.             terrain.Flush();
59.             terrain1.Flush();
60.         }
61.  
62.         Terrain.SetConnectivityDirty();
63.  
64.         Debug.Log("Terrain.activeTerrains: " + Terrain.activeTerrains.Length);
65.         Debug.Log("terrain.allowAutoConnect: " + terrain.allowAutoConnect);
66.         Debug.Log("terrain.groupingID: " + terrain.groupingID);
67.  
68.         Debug.Log("terrain.rightNeighbor new: " + terrain.rightNeighbor);
69.         Debug.Log("terrain.leftNeighbor new: " + terrain.leftNeighbor);
70.         Debug.Log("terrain.topNeighbor new: " + terrain.topNeighbor);
71.         Debug.Log("terrain.bottomNeighbor new: " + terrain.bottomNeighbor);
72.     }

I don't have much time before my project deadline, so I would really appreciate some quick help! Thanks in advance.

 

@Mytino The problem in your code looks straightforward. The faulty behaviour comes obviously from the position of the chunks, so the "chunk.transform.position" logic must be faulty. I'm not sure about the actual algorythm that's gonna fix the issue, but here's a few ideas:

Code (CSharp):

1.  
2. // This will give a value of how many vectors does it take to travel 1 heightmap.
3. Vector2 heightmap_to_vector = new Vector2(terrain_size.x / heightmap_resolution, terrain_size.z / heightmap_resolution);
4.  
5. // Possible fixes, if none of these work the logic for the actual fix will most likely be similar nonetheless. You're looking for the correct number to offset each terrain. Right now that number is too big.
6.  
7. // Possible solution 1
8. chunk.transform.position = new Vector3(chunkX * (chunkSize.x - heightmap_to_vector .x), 0f, chunkY * (chunkSize.y - heightmap_to_vector.y));
9.  
10. // Possible solution 2
11. chunk.transform.position = new Vector3(chunkX * (chunkSize.x - chunkX * heightmap_to_vector .x), 0f, chunkY * (chunkSize.y - chunkY * heightmap_to_vector.y));
12.  

As for syncing terrain's by grouping, at least in my experience, unity does all of that for you as long as you make terrain positions, heightmap resolution and maximum terrain height uniform.

 

Thank you, but I already tried this. This is what I meant by "I tried just nudging their positions a bit, but that doesn't solve it as textures and lighting still is disconnected."

I would expect textures as well as geometries to seamlessly connect and they don't connect in any way. Interestingly enough, the scene view makes it seem like they're connected, as it only highlights terrains around the existing terrains when the "Create neighbor terrains" tool is active, as can be seen here:


Here I also tried creating a new terrain (lower right), but as you can see, it didn't connect, and it shows an error message which seem to be an Unity-side bug.

 

@Mytino this might be a bit of a longer conversation for this type of bug. Check in with discord channels. https://discordapp.com/channels/85338836384628736/85593628650504192 and https://discordapp.com/channels/493510779866316801/493511037421879316 for faster answers to dev questions. Are those terrains painted already in a different program or are they made via some kind of perlin noise? If they're made via perlin noise then i'd suggest to offset the heightmap coordinates similarly to the offset you applied to the terrain positions. Also i've noticed that the edges of some of the terrains are going straight down, which indicate that the first Y and X rows of the heightmap are set to 0.

 

Thank you for the links! The terrains were initially generated with gradient noise, but I've ran each of them through a neural net afterwards, which is why they're so disconnected at the edges. The edges go straight down on two of the four sides only. I just thought it was default when it wasn't connected, so interesting to know it means they're 0, thanks!

Edit: The links don't seem to lead anywhere?

Edit 2:
Clamping the edge where heights were 0 looks much better, and it seems like the lighting/pattern disconnect is actually fixed. The only issue is that the heightmaps don't automatically stitch together, so I will have to go through the neighbors and copy over their edge values if I want to get it perfect. Thanks again!

 

If we are adding terrain to the scene at runtime, am I correct that we will need to connect the terrains the old fashion way using SetNeighbors?

I just want to make sure that there is no way to make use of the grouping ids and auto connection magic at runtime (for terrains that don't exist before the scene is loaded).

And if indeed SetNeighbors needs to be used, is there any issue with connecting terrain that don't have the same Grouping ID? I don't foresee this being an actual issue, but if it is a hard fast rule that SetNeighbors will now only work on terrain with the same Grouping ID, I want to know so I can warn the users of my Asset Store tools.

 

I'll answer my own question, SetNeighbors does not seems to work anymore on Unity 2018.4 and up (though probably the issue was introduced with 2018.3 when Terrain Groups were introduced).

I'm uploading a package that you can import into Unity 2018.4 or above version of Unity to see the issue. There's two scenes, one where AutoConnect is enabled and one where it is disabled and SetNeighbors is called manually. AutoConnect works on the terrain while SetNeighbors manual call does not. It makes no sense to me but it is what it is.

Edit: Have to tag you wyattt_ and ChrisTchou in the hopes for getting help for this, as I've tried elsewhere on the forums and can't get a nibble from anyone Unity related.

Edit 2: Here is a thread I started about the issue: https://forum.unity.com/threads/ter...ducible-example-attached.871693/#post-5893550

 

I think I have finally figured out what is happening. The Auto Connect feature has a method under the hood that performs the magic of setting all the neighbors that utilize the Auto Connect option. This method is seemingly called in one of the first two frames upon entering your game, and then any time a terrain is added or removed from the scene, regardless of whether any terrain in the scene has the auto connection option enabled/disabled.

Now, this should not be an issue, because the AutoConnect method should exit if it detects no terrain are utilizing the auto connect option. Unfortunately, it doesn't do this. Instead, it proceeds to reset the neighbors of EVERY terrain in the scene, no matter if it is utilizing auto connect.

So, let's say you have a static scene with some number of terrain, and for whatever reason you are manually setting the neighbors via SetNeighbors. To get around the issue with Auto Connect, all you need to do is wait until Time.frameCount = 3 or more before setting the neighbors, because by this time the magic AutoConnect method will have run and you can safely set the neighbors without fear of them being reset.

However, if you are in the more likely situation of adding/removing terrain at runtime, you only have the poor option of resetting the neighbors of all terrain in the scene after the Auto Connect method has run and wreaked its havoc. If you have multiple terrain being added/removed in quick succession, I recommend waiting until after the last has finished being added/removed before performing the re-neighboring. Unfortunately, this means there will be a very brief time where the seems between neighbors is visible, however there is no way to get around this, because the only alternative is to call SetNeighbors on all terrain in a single frame (the technique employed by AutoConnect), which is not performant and would defeat the whole purpose of manually setting the neighbors in the first place.

Unity, please fix this. It is such a simple fix, it would take less than 10 lines of code probably.

 

Going to add onto my own posts. After further investigation I hoped to be able to solve the issue by trying to detect when the terrain neighbors are cleared automatically and resetting the neighbors ASAP for terrain that are in view of a working camera.

This kind of works however there is a strange issue where the terrain flickers occasionally. I'm not sure why that happens, the code for fixing the neighbors executes in the RenderPipelineManager.endFrameRendering event.

My investigation also found that the AutoConnect is called by Unity during the render step, before culling and rendering terrain in the scene. My guess is Unity checks the Active Terrains in the scene and sees if they have changed, and fires off the Auto Connect method if they have. Since everything is done in this render step, I don't believe there is a way to interject the neighbor resetting code in between the call to AutoConnect and the rendering of the terrain.

Therefore, I believe the best way to resolve this issue is to modify the Auto Connect code in the way I described in the comment section of this bug report:

Edit: Submitted a new bug because the old one was removed without comment. Here is the link:
https://fogbugz.unity3d.com/default.asp?1393860_3031p009t2hitemt

 

Bumping because I have not heard a single word on this issue, which is a shame because the code fix is so simple to implement.

 

Okay, so I finally received an update about this issue. Apparently the bug page was moved but there was an error and I was not notified.

This is the new page: https://issuetracker.unity3d.com/is...boring-terrain-using-terrain-dot-setneighbors

The issue has been fixed in the following Unity versions:
2019.4.33f1
2020.3.23f1
2021.1.0a1 and above

Great news!

 

what you want is to check the box auto connect in the terrain settings, this will solve your issue

 

Who are you replying to?

 

the poster to the question

 

Okay, well terrain neighboring was not that users issue.

Their problem is they thought that so long as they set the neighbors for the terrain, when they called SetHeights on that terrain the other neighboring terrains would have their heights adjusted automatically, which is not the case.

As the devs commented, setting the neighbors properly (either via SetNeighbors or using Auto Connect) accomplishes two things:

1. It allows the terrain editor code to know which terrain are next to each other, so that when you perform operations on the edges of the terrain those operations affect all terrain on the edge.
2. It allows LODs on different terrain to match across tile borders.