In-game Terrain Heightmap Editor for Unity

Unity comes equipped with a built-in Terrain editor, but what if you want to add a Terrain editing feature in the game?

In this tutorial, I will be showing how to add a simple runtime Terrain editor. Also, it does not include texturing, it's still a great example that you can build upon.

Runtime Terrain editor in Unity

Unity version used in this tutorial: Unity 2021.1.0f1 (64-bit)

Step 1: Create all the necessary scripts

This tutorial features 3 scripts:

SC_TerrainEditor.cs

using UnityEngine;

public class SC_TerrainEditor : MonoBehaviour
{
    public enum DeformMode { RaiseLower, Flatten, Smooth }
    DeformMode deformMode = DeformMode.RaiseLower;
    string[] deformModeNames = new string[] { "Raise Lower", "Flatten", "Smooth" };

    public Terrain terrain;
    public Texture2D deformTexture;
    public float strength = 1;
    public float area = 1;
    public bool showHelp;

    Transform buildTarget;
    Vector3 buildTargPos;
    Light spotLight;

    //GUI
    Rect windowRect = new Rect(10, 10, 400, 185);
    bool onWindow = false;
    bool onTerrain;
    Texture2D newTex;
    float strengthSave;

    //Raycast
    private RaycastHit hit;

    //Deformation variables
    private int xRes;
    private int yRes;
    private float[,] saved;
    float flattenTarget = 0;
    Color[] craterData;

    TerrainData tData;

    float strengthNormalized
    {
        get
        {
            return (strength) / 9.0f;
        }
    }

    // Start is called before the first frame update
    void Start()
    {
        //Create build target object
        GameObject tmpObj = new GameObject("BuildTarget");
        buildTarget = tmpObj.transform;

        //Add Spot Light to build target
        GameObject spotLightObj = new GameObject("SpotLight");
        spotLightObj.transform.SetParent(buildTarget);
        spotLightObj.transform.localPosition = new Vector3(0, 2, 0);
        spotLightObj.transform.localEulerAngles = new Vector3(90, 0, 0);
        spotLight = spotLightObj.AddComponent<Light>();
        spotLight.type = LightType.Spot;
        spotLight.range = 20;

        tData = terrain.terrainData;
        if (tData)
        {
            //Save original height data
            xRes = tData.heightmapResolution;
            yRes = tData.heightmapResolution;
            saved = tData.GetHeights(0, 0, xRes, yRes);
        }

        //Change terrain layer to UI
        terrain.gameObject.layer = 5;
        strength = 2;
        area = 2;
        brushScaling();
    }

    void FixedUpdate()
    {
        raycastHit();
        wheelValuesControl();

        if (onTerrain && !onWindow)
        {
            terrainDeform();
        }

        //Update Spot Light Angle according to the Area value
        spotLight.spotAngle = area * 25f;
    }

    //Raycast
    //______________________________________________________________________________________________________________________________
    void raycastHit()
    {
        Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        hit = new RaycastHit();
        //Do Raycast hit only against UI layer
        if (Physics.Raycast(ray, out hit, 300, 1 << 5))
        {
            onTerrain = true;
            if (buildTarget)
            {
                buildTarget.position = Vector3.Lerp(buildTarget.position, hit.point + new Vector3(0, 1, 0), Time.time);
            }
        }
        else
        {
            if (buildTarget)
            {
                Vector3 curScreenPoint = new Vector3(Input.mousePosition.x, Input.mousePosition.y, 200);
                Vector3 curPosition = Camera.main.ScreenToWorldPoint(curScreenPoint);
                buildTarget.position = curPosition;
                onTerrain = false;
            }
        }
    }

    //TerrainDeformation
    //___________________________________________________________________________________________________________________
    void terrainDeform()
    {
        if (Input.GetMouseButtonDown(0))
        {
            buildTargPos = buildTarget.position - terrain.GetPosition();
            float x = Mathf.Clamp01(buildTargPos.x / tData.size.x);
            float y = Mathf.Clamp01(buildTargPos.z / tData.size.z);
            flattenTarget = tData.GetInterpolatedHeight(x, y) / tData.heightmapScale.y;
        }

        //Terrain deform
        if (Input.GetMouseButton(0))
        {

            buildTargPos = buildTarget.position - terrain.GetPosition();

            if (Input.GetKey(KeyCode.LeftShift))
            {
                strengthSave = strength;
            }
            else
            {
                strengthSave = -strength;
            }

            if (newTex && tData && craterData != null)
            {
                int x = (int)Mathf.Lerp(0, xRes, Mathf.InverseLerp(0, tData.size.x, buildTargPos.x));
                int z = (int)Mathf.Lerp(0, yRes, Mathf.InverseLerp(0, tData.size.z, buildTargPos.z));
                x = Mathf.Clamp(x, newTex.width / 2, xRes - newTex.width / 2);
                z = Mathf.Clamp(z, newTex.height / 2, yRes - newTex.height / 2);
                int startX = x - newTex.width / 2;
                int startY = z - newTex.height / 2;
                float[,] areaT = tData.GetHeights(startX, startY, newTex.width, newTex.height);
                for (int i = 0; i < newTex.height; i++)
                {
                    for (int j = 0; j < newTex.width; j++)
                    {
                        if (deformMode == DeformMode.RaiseLower)
                        {
                            areaT[i, j] = areaT[i, j] - craterData[i * newTex.width + j].a * strengthSave / 15000;
                        }
                        else if (deformMode == DeformMode.Flatten)
                        {
                            areaT[i, j] = Mathf.Lerp(areaT[i, j], flattenTarget, craterData[i * newTex.width + j].a * strengthNormalized);
                        }
                        else if (deformMode == DeformMode.Smooth)
                        {
                            if (i == 0 || i == newTex.height - 1 || j == 0 || j == newTex.width - 1)
                                continue;

                            float heightSum = 0;
                            for (int ySub = -1; ySub <= 1; ySub++)
                            {
                                for (int xSub = -1; xSub <= 1; xSub++)
                                {
                                    heightSum += areaT[i + ySub, j + xSub];
                                }
                            }

                            areaT[i, j] = Mathf.Lerp(areaT[i, j], (heightSum / 9), craterData[i * newTex.width + j].a * strengthNormalized);
                        }
                    }
                }
                tData.SetHeights(x - newTex.width / 2, z - newTex.height / 2, areaT);
            }
        }
    }

    void brushScaling()
    {
        //Apply current deform texture resolution 
        newTex = Instantiate(deformTexture) as Texture2D;
        TextureScale.Point(newTex, deformTexture.width * (int)area / 10, deformTexture.height * (int)area / 10);
        newTex.Apply();
        craterData = newTex.GetPixels();
    }

    void wheelValuesControl()
    {
        float mouseWheel = Input.GetAxis("Mouse ScrollWheel");
        if (Mathf.Abs(mouseWheel) > 0.0)
        {
            if (mouseWheel > 0.0)
            {
                //More
                if (!Input.GetKey(KeyCode.LeftShift))
                {
                    if (area < 13)
                    {
                        area += 0.5f;
                    }
                    else
                    {
                        area = 13;
                    }
                }
                else
                {
                    if (strength < 13)
                    {
                        strength += 0.5f;
                    }
                    else
                    {
                        strength = 13;
                    }
                }
            }
            else if (mouseWheel < 0.0)
            {
                //Less
                if (!Input.GetKey(KeyCode.LeftShift))
                {
                    if (area > 1)
                    {
                        area -= 0.5f;
                    }
                    else
                    {
                        area = 1;
                    }
                }
                else
                {
                    if (strength > 1)
                    {
                        strength -= 0.5f;
                    }
                    else
                    {
                        strength = 1;
                    }
                }
            }
            if (area > 1)
                brushScaling();
        }
    }

    //GUI
    //______________________________________________________________________________________________________________________________
    void OnGUI()
    {
        windowRect = GUI.Window(0, windowRect, TerrainEditorWindow, "Terrain Sculptor");

        GUILayout.BeginArea(new Rect(Screen.width - 70, 10, 60, 30));
        showHelp = GUILayout.Toggle(showHelp, "(Help)", new GUILayoutOption[] { GUILayout.Width(60.0f), GUILayout.Height(30.0f) });
        GUILayout.EndArea();

        if (showHelp)
        {
            //Help window properties
            GUI.Window(1, new Rect(Screen.width - 410, 50, 400, 120), HelpWindow, "Help Window");
        }
    }

    //Help window display tips and tricks
    void HelpWindow(int windowId)
    {
        GUILayout.BeginVertical("box");
        {
            GUILayout.Label("- Mouse wheel - area change");
            GUILayout.Label("- Mouse wheel + Shift - strength change");
            GUILayout.Label("- Hold Shift in RaiseLower mode to lower terrain");
        }
        GUILayout.EndVertical();
    }

    void TerrainEditorWindow(int windowId)
    {
        //Detect when mouse cursor inside region (TerrainEditorWindow)
        GUILayout.BeginArea(new Rect(0, 0, 400, 240));
        if (GUILayoutUtility.GetRect(10, 50, 400, 240).Contains(Event.current.mousePosition))
        {
            onWindow = true;
        }
        else
        {
            onWindow = false;
        }
        GUILayout.EndArea();

        GUILayout.BeginVertical();

        //Shared GUI
        GUILayout.Space(10f);
        GUILayout.BeginHorizontal();
        GUILayout.Label("Area:", new GUILayoutOption[] { GUILayout.Width(75f) });
        area = GUILayout.HorizontalSlider(area, 1f, 13f, new GUILayoutOption[] { GUILayout.Width(250f), GUILayout.Height(15f) });
        GUILayout.Label((Mathf.Round(area * 100f) / 100f).ToString(), new GUILayoutOption[] { GUILayout.Width(250f), GUILayout.Height(20f) });
        //Change brush texture size if area value was changed
        if (GUI.changed)
        {
            brushScaling();
        }
        GUILayout.EndHorizontal();

        GUILayout.Space(10f);
        GUILayout.BeginHorizontal();
        GUILayout.Label("Strength:", new GUILayoutOption[] { GUILayout.Width(75f) });
        strength = GUILayout.HorizontalSlider(strength, 1f, 13f, new GUILayoutOption[] { GUILayout.Width(250f), GUILayout.Height(15f) });
        GUILayout.Label((Mathf.Round(strength * 100f) / 100f).ToString(), new GUILayoutOption[] { GUILayout.Width(250f), GUILayout.Height(20f) });
        GUILayout.EndHorizontal();

        //Deform GUI
        GUILayout.Space(10);

        deformMode = (DeformMode)GUILayout.Toolbar((int)deformMode, deformModeNames, GUILayout.Height(25));

        GUILayout.Space(10);

        GUILayout.BeginHorizontal();
        if (GUILayout.Button("Reset Terrain Height", new GUILayoutOption[] { GUILayout.Height(30f) }))
        {
            tData.SetHeights(0, 0, saved);
        }
        GUILayout.EndHorizontal();

        GUILayout.EndVertical();
    }

    void OnApplicationQuit()
    {
        //Reset terrain height when exiting play mode
        tData.SetHeights(0, 0, saved);
    }
}

SC_EditorFlyCamera.cs

using UnityEngine;

public class SC_EditorFlyCamera : MonoBehaviour
{
    public float moveSpeed = 15;
    public float turnSpeed = 3;

    bool freeLook = false;
    bool moveFast = false;
    float rotationY;

    // Use this for initialization
    void Start()
    {
        rotationY = -transform.localEulerAngles.x;
    }

    // Update is called once per frame
    void Update()
    {
        Movement();
    }

    void Movement()
    {
        moveFast = Input.GetKey(KeyCode.LeftShift);

        float speed = moveSpeed * Time.deltaTime * (moveFast ? 3 : 1);

        if (Input.GetKey(KeyCode.W))
        {
            transform.root.Translate(transform.forward * speed, Space.World);
        }
        if (Input.GetKey(KeyCode.S))
        {
            transform.root.Translate(-transform.forward * speed, Space.World);
        }
        if (Input.GetKey(KeyCode.A))
        {
            transform.root.Translate(-transform.right * speed, Space.World);
        }
        if (!Input.GetKey(KeyCode.LeftControl) && Input.GetKey(KeyCode.D))
        {
            transform.root.Translate(transform.right * speed, Space.World);
        }
        if (Input.GetKey(KeyCode.Q))
        {
            transform.root.Translate(transform.up * speed, Space.World);
        }
        if (Input.GetKey(KeyCode.E))
        {
            transform.root.Translate(-transform.up * speed, Space.World);
        }

        if (Input.GetMouseButtonDown(1))
        {
            Cursor.lockState = CursorLockMode.Locked;
            Cursor.visible = false;
        }
        freeLook = Input.GetMouseButton(1);
        if (Input.GetMouseButtonUp(1))
        {
            Cursor.lockState = CursorLockMode.None;
            Cursor.visible = true;
        }

        if (freeLook)
        {
            float rotationX = transform.localEulerAngles.y + Input.GetAxis("Mouse X") * turnSpeed;

            rotationY += Input.GetAxis("Mouse Y") * turnSpeed;
            rotationY = Mathf.Clamp(rotationY, -90, 90);

            transform.localEulerAngles = new Vector3(-rotationY, rotationX, 0);
        }
    }
}

TextureScale.cs

// Only works on ARGB32, RGB24 and Alpha8 textures that are marked readable

using System.Threading;
using UnityEngine;

public class TextureScale
{
    public class ThreadData
    {
        public int start;
        public int end;
        public ThreadData(int s, int e)
        {
            start = s;
            end = e;
        }
    }

    private static Color[] texColors;
    private static Color[] newColors;
    private static int w;
    private static float ratioX;
    private static float ratioY;
    private static int w2;
    private static int finishCount;
    private static Mutex mutex;

    public static void Point(Texture2D tex, int newWidth, int newHeight)
    {
        ThreadedScale(tex, newWidth, newHeight, false);
    }

    public static void Bilinear(Texture2D tex, int newWidth, int newHeight)
    {
        ThreadedScale(tex, newWidth, newHeight, true);
    }

    private static void ThreadedScale(Texture2D tex, int newWidth, int newHeight, bool useBilinear)
    {
        texColors = tex.GetPixels();
        newColors = new Color[newWidth * newHeight];
        if (useBilinear)
        {
            ratioX = 1.0f / ((float)newWidth / (tex.width - 1));
            ratioY = 1.0f / ((float)newHeight / (tex.height - 1));
        }
        else
        {
            ratioX = ((float)tex.width) / newWidth;
            ratioY = ((float)tex.height) / newHeight;
        }
        w = tex.width;
        w2 = newWidth;
        var cores = Mathf.Min(SystemInfo.processorCount, newHeight);
        var slice = newHeight / cores;

        finishCount = 0;
        if (mutex == null)
        {
            mutex = new Mutex(false);
        }
        if (cores > 1)
        {
            int i = 0;
            ThreadData threadData;
            for (i = 0; i < cores - 1; i++)
            {
                threadData = new ThreadData(slice * i, slice * (i + 1));
                ParameterizedThreadStart ts = useBilinear ? new ParameterizedThreadStart(BilinearScale) : new ParameterizedThreadStart(PointScale);
                Thread thread = new Thread(ts);
                thread.Start(threadData);
            }
            threadData = new ThreadData(slice * i, newHeight);
            if (useBilinear)
            {
                BilinearScale(threadData);
            }
            else
            {
                PointScale(threadData);
            }
            while (finishCount < cores)
            {
                Thread.Sleep(1);
            }
        }
        else
        {
            ThreadData threadData = new ThreadData(0, newHeight);
            if (useBilinear)
            {
                BilinearScale(threadData);
            }
            else
            {
                PointScale(threadData);
            }
        }

        tex.Resize(newWidth, newHeight);
        tex.SetPixels(newColors);
        tex.Apply();

        texColors = null;
        newColors = null;
    }

    public static void BilinearScale(System.Object obj)
    {
        ThreadData threadData = (ThreadData)obj;
        for (var y = threadData.start; y < threadData.end; y++)
        {
            int yFloor = (int)Mathf.Floor(y * ratioY);
            var y1 = yFloor * w;
            var y2 = (yFloor + 1) * w;
            var yw = y * w2;

            for (var x = 0; x < w2; x++)
            {
                int xFloor = (int)Mathf.Floor(x * ratioX);
                var xLerp = x * ratioX - xFloor;
                newColors[yw + x] = ColorLerpUnclamped(ColorLerpUnclamped(texColors[y1 + xFloor], texColors[y1 + xFloor + 1], xLerp),
                                                       ColorLerpUnclamped(texColors[y2 + xFloor], texColors[y2 + xFloor + 1], xLerp),
                                                       y * ratioY - yFloor);
            }
        }

        mutex.WaitOne();
        finishCount++;
        mutex.ReleaseMutex();
    }

    public static void PointScale(System.Object obj)
    {
        ThreadData threadData = (ThreadData)obj;
        for (var y = threadData.start; y < threadData.end; y++)
        {
            var thisY = (int)(ratioY * y) * w;
            var yw = y * w2;
            for (var x = 0; x < w2; x++)
            {
                newColors[yw + x] = texColors[(int)(thisY + ratioX * x)];
            }
        }

        mutex.WaitOne();
        finishCount++;
        mutex.ReleaseMutex();
    }

    private static Color ColorLerpUnclamped(Color c1, Color c2, float value)
    {
        return new Color(c1.r + (c2.r - c1.r) * value,
                          c1.g + (c2.g - c1.g) * value,
                          c1.b + (c2.b - c1.b) * value,
                          c1.a + (c2.a - c1.a) * value);
    }
}

Step 2

Create new Scene
Create new Terrain by going to GameObject->3D Object->Terrain
Attach SC_EditorFlyCamera and SC_TerrainEditor scripts to the Main Camera
Assign Terrain and DeformTexture variables in SC_TerrainEditor (Terrain should be the one you want to edit in the scene)

For DeformTexture you can use the image below or you can use these high-quality Terrain Brushes:

NOTE: Deform Texture must have Alpha source from Grayscale, Read/Write Enabled and also the format must be set to one of these: ARGB32, RGB24 or Alpha8.