C# Prefab Terrain Modification Runtime (Helping others to understand Beginner)

Hi Unity Pros,

Disclamer: This is most likely a solution to help guide you and is not an end all type of thing (I'm a beginner too, you know), and I didn't really know where else to post this.

As the title mentions "Helping others to understand Beginner" I struggled for about two years learning how the world (heck) do I modify terrain with a prefab. After taking 6 month break from it, looking at dozens of forums, and many youtube videos I was able to piece together a entry level solution (I'm not the smartest crayon in the box, you know).

This was done in Unity3d 2019.2.1f1

Firstly, I placed a box as my reference source (as all I wanted was to get a square terrain area for placing objects), rigidbody, and two box colliders (one trigger and the other not a trigger), and set the terrain tag to "Terrain".

The Script:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class Object_Terrain_Modifiy : MonoBehaviour
6. {
7.     public Terrain terrain; //get terrain to manipulate
8.     public float strength = 0.001f; //keep the strength low as we are working in [0, 1] increments as 1 is maximum
9.     public float Ray_distance = 2f; // get raycast distance from Gameobject
10.  
11.     private int heightmapWidth; //map width
12.     private int heightmapHeight; //map height
13.     private float[,] heights; //still don't know what this really does
14.     private TerrainData terrainData; //all the data ever needed for terrains
15.  
16.  
17.     // Baisically call everything so we can work with the terrain in the start function
18.     void Start()
19.     {
20.         terrainData = terrain.terrainData;
21.  
22.         heightmapHeight = terrainData.heightmapHeight;
23.         heightmapWidth = terrainData.heightmapWidth;
24.         heights = terrainData.GetHeights(0, 0, heightmapWidth, heightmapHeight);
25.     }
26.  
27.     // I used fix so it is more smooth with how the terrain is leveled (as this costs cpu resources)
28.     void FixedUpdate()
29.     {
30.         RaycastHit hit;
31.      
32.             //if raycast from object is either above/below find what it hits
33.             //AND make sure we hit a tag for "Terrain"
34.             if (Physics.Raycast(this.gameObject.transform.position, -Vector3.up, out hit, Ray_distance) || Physics.Raycast(this.gameObject.transform.position, Vector3.up, out hit))
35.             {
36.             if (hit.point.y < (this.gameObject.transform.position.y - (this.gameObject.transform.localScale.y / 2)) && hit.collider.tag == "Terrain")
37.             {
38.                 //raise terrain
39.                 RaiseTerrain(hit.point);
40.             }
41.          
42.  
43.             if (hit.point.y > (this.gameObject.transform.position.y - (this.gameObject.transform.localScale.y / 2)) + 0.5f && hit.collider.tag == "Terrain")
44.             {
45.                 //lower terrain
46.                 LowerTerrain(hit.point);
47.             }
48.  
49.             // if the terrain hit spot is not too high or low turn off script so we don't waste resources on manipulating the terrain anymore
50.             if (!(hit.point.y < (this.gameObject.transform.position.y - (this.gameObject.transform.localScale.y / 2))) && (!(hit.point.y > (this.gameObject.transform.position.y - (this.gameObject.transform.localScale.y / 2)) + 0.5f)) && hit.collider.tag == "Terrain")
51.             {
52.                 this.gameObject.GetComponent<Object_Terrain_Modifiy>().enabled = false;
53.             }
54.  
55.         }
56.  
57.             //see in real time when we move the box where we are attempting to hit
58.         Debug.DrawRay(this.gameObject.transform.position, -Vector3.up, Color.red, Ray_distance);
59.     }
60.  
61.     private void RaiseTerrain(Vector3 point)
62.     {
63.         //get the world coordinate of our hit location and convert it to terrain location
64.         int mouseX = (int)((point.x / terrainData.size.x) * heightmapWidth);
65.         int mouseZ = (int)((point.z / terrainData.size.z) * heightmapHeight);
66.  
67.         Debug.Log("what is X: " + mouseX); //check to see if we are in the right area
68.         Debug.Log("what is Z: " + mouseZ); //check to see if we are in the right area
69.  
70.         float[,] modifiedHeights = new float[1, 1]; //set the maximum heights to 1 as we want to make sure we can manipulate the terrain at any height level
71.         float y = heights[mouseX, mouseZ]; //unsure still of what heights[,] really accomplishes
72.  
73.      
74.         //raise terrain
75.             y += strength * Time.deltaTime;
76.      
77.  
78.      
79.         //if object is higher than terrain max height spot increasing terrain.
80.         if (y > terrainData.size.y)
81.         {
82.             y = terrainData.size.y;
83.         }
84.  
85.         //get our lowest point that we want to start in
86.         modifiedHeights[0, 0] = y;
87.  
88.      
89.         // this is where the magic terrain manipulation magic starts to happen //
90.         // I set both i & z to a negative scale value to create a starting point behind and away from the box, and keep adjusting terrain till it is positively over the box's area
91.         for (int i = -(int)this.gameObject.transform.localScale.x; i < (this.gameObject.transform.localScale.x * 2); i++)
92.         {
93.             for (int z = -(int)this.gameObject.transform.localScale.z; z < (this.gameObject.transform.localScale.z * 2); z++)
94.             {
95.                 heights[mouseX - i, mouseZ - z] = y;
96.                 terrainData.SetHeights(mouseX - i, mouseZ - z, modifiedHeights);
97.             }
98.         }
99.  
100.  
101.     }
102.  
103.     //does pretty much the opposite but it does it very very fast (still the work in progress part of the script)
104.     private void LowerTerrain(Vector3 point)
105.     {
106.         int mouseX = (int)((point.x / terrainData.size.x) * heightmapWidth);
107.         int mouseZ = (int)((point.z / terrainData.size.z) * heightmapHeight);
108.  
109.         float[,] modifiedHeights = new float[1, 1];
110.         float y = heights[mouseX, mouseZ];
111.         y -= strength * Time.deltaTime;
112.  
113.         if (y < terrainData.size.y)
114.         {
115.             y = 0;
116.         }
117.  
118.         modifiedHeights[0, 0] = y;
119.      
120.         for (int i = -(int)this.gameObject.transform.localScale.x; i < (this.gameObject.transform.localScale.x * 2); i++)
121.         {
122.             for (int z = -(int)this.gameObject.transform.localScale.z; z < (this.gameObject.transform.localScale.z * 2); z++)
123.             {
124.                 heights[mouseX - i, mouseZ - z] = y;
125.                 terrainData.SetHeights(mouseX - i, mouseZ - z, modifiedHeights);
126.             }
127.         }
128.  
129.     }
130. }

The end result in the png picture.