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Question Spawn game object randomly on terrain

Discussion in 'Editor & General Support' started by ziptie_entity, Oct 7, 2023.

  1. ziptie_entity


    Jun 3, 2018

    I am making a procedural island generator and it all works fine however I am trying to get the player to spawn on the island by getting each the height at each position on the terrain checking if it is above a certain threshold.
    This works however when I run the code, the player spawns in the incorrect X and Z position (the Y position seems to be fine however). I feel like it is something with the heightmap and the world position not aligning correctly, though I am not sure.

    Here is the code to get a random position on the terrain based off of the height (The Texture2D and Stopwatch part is just for debugging):
    Code (CSharp):
    1. public static Vector3 GetRandomIslandPosition(int islandNumber, int maxHeight = 50, int minHeight = 30)
    2. {
    3.     var sw = new Stopwatch();
    4.     sw.Start();
    5.     List<Vector3> positions = new List<Vector3>();
    6.     var island = IslandManager.instance.Find(islandNumber);
    7.     float[,] heights = island.TerrainData.GetHeights(0, 0, instance.TerrainSettings.HeightMapResolution, instance.TerrainSettings.HeightMapResolution);
    9.     instance.island = new Texture2D(2000,2000);
    11.     for (int x = 0; x < instance.TerrainSettings.HeightMapResolution; x++)
    12.     {
    13.         for (int y = 0; y < instance.TerrainSettings.HeightMapResolution; y++)
    14.         {
    15.             float heightTerrain = heights[x, y]*100;
    16.             float heightWorld = (heightTerrain/100) * instance.TerrainSettings.TerrainHeight;
    18.             if (heightTerrain < maxHeight && heightTerrain > minHeight)
    19.             {
    20.                 float normX = (float)x / (float)instance.TerrainSettings.HeightMapResolution;
    21.                 float normY = (float)y / (float)instance.TerrainSettings.HeightMapResolution;
    23.                 Vector3 worldPos = new Vector3(normX * (float)instance.TerrainSettings.TerrainSize, heightWorld, normY * (float)instance.TerrainSettings.TerrainSize);
    24.                 positions.Add(worldPos);
    25.                 instance.island.SetPixel(Mathf.FloorToInt(normX * (float)instance.TerrainSettings.TerrainSize), Mathf.FloorToInt(normY * (float)instance.TerrainSettings.TerrainSize),;
    26.             }
    27.         }
    28.     }
    29.     var selectedPosition = island.transform.position + positions[UnityEngine.Random.Range(0, positions.Count)];
    30.     instance.island.Apply();
    31.     Debug.LogFormat("Method completed in {0} seconds", sw.Elapsed.TotalSeconds);
    32.     sw.Stop();
    33.     return selectedPosition;
    34. }
  2. Kurt-Dekker


    Mar 16, 2013
    That can only mean it is...

    Time to start debugging! Here is how you can begin your exciting new debugging adventures:

    You must find a way to get the information you need in order to reason about what the problem is.

    Once you understand what the problem is, you may begin to reason about a solution to the problem.

    What is often happening in these cases is one of the following:

    - the code you think is executing is not actually executing at all
    - the code is executing far EARLIER or LATER than you think
    - the code is executing far LESS OFTEN than you think
    - the code is executing far MORE OFTEN than you think
    - the code is executing on another GameObject than you think it is
    - you're getting an error or warning and you haven't noticed it in the console window

    To help gain more insight into your problem, I recommend liberally sprinkling
    statements through your code to display information in realtime.

    Doing this should help you answer these types of questions:

    - is this code even running? which parts are running? how often does it run? what order does it run in?
    - what are the names of the GameObjects or Components involved?
    - what are the values of the variables involved? Are they initialized? Are the values reasonable?
    - are you meeting ALL the requirements to receive callbacks such as triggers / colliders (review the documentation)

    Knowing this information will help you reason about the behavior you are seeing.

    You can also supply a second argument to Debug.Log() and when you click the message, it will highlight the object in scene, such as

    If your problem would benefit from in-scene or in-game visualization, Debug.DrawRay() or Debug.DrawLine() can help you visualize things like rays (used in raycasting) or distances.

    You can also call Debug.Break() to pause the Editor when certain interesting pieces of code run, and then study the scene manually, looking for all the parts, where they are, what scripts are on them, etc.

    You can also call GameObject.CreatePrimitive() to emplace debug-marker-ish objects in the scene at runtime.

    You could also just display various important quantities in UI Text elements to watch them change as you play the game.

    Visit Google for how to see console output from builds. If you are running a mobile device you can also view the console output. Google for how on your particular mobile target, such as this answer for iOS: or this answer for Android:

    If you are working in VR, it might be useful to make your on onscreen log output, or integrate one from the asset store, so you can see what is happening as you operate your software.

    Another useful approach is to temporarily strip out everything besides what is necessary to prove your issue. This can simplify and isolate compounding effects of other items in your scene or prefab.

    If your problem is with OnCollision-type functions, print the name of what is passed in!

    Here's an example of putting in a laser-focused Debug.Log() and how that can save you a TON of time wallowing around speculating what might be going wrong:

    "When in doubt, print it out!(tm)" - Kurt Dekker (and many others)

    Note: the
    function is an alias for Debug.Log() provided by the MonoBehaviour class.
  3. ziptie_entity


    Jun 3, 2018
    After modifying the code to spawn a primitive sphere every 100 iterations of the loop, I can confirm the the heights are not accurate to the actual terrain heights. Still have no idea why this is happening.
  4. Kurt-Dekker


    Mar 16, 2013
    This will continue to be the case until you:

    - get unbelievably lucky

    - learn how to debug.

    See the above for how to debug.

    If you want another example of terrain heights and working with the various coordinate systems involved (there are at least three: world, local and "heightmap..." go read the TerrainData docs for more), check this little utility out:

    Full code: