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Alto's Adventure Style Procedural Surface Generation Part 1


Alto's Adventure Style - Procedural Surface Generation

A Screenshot of Alto's Adventure Gameplay
This game appears to be a strictly 2D game but if you have played it enough you will notice that some of the art assets used look like it's 3D ( I don't know if they are tho ). If you haven't played the game you are missing out on one the most visually pleasing and calming games out there ( There is literally a mode called Zen mode in the game ).
Anyway, I am going to show you how to make a procedural 2D world ( without the trees, buildings and background ) like in Alto's Adventure.
But you may notice I have a plane which is in in the Z-axis giving a depth to the surface which is not there in Alto's Adventure but if you want to know how to do it then that will be in part 2.
To achieve the same effect of Alto's Adventure ( I'm leaving that up to you ) only minimal changes are needed to the code that I am going to explain.
We are going to be using the plane mesh in unity for creating the 2D surface as the plane comes with 10 vertices along both it's width and height.
So modifying them will be easy because we know how many vertices are there on each row of the mesh.
This inside a class called 'SurfaceGenerator', you can call it whatever you want but remember that this class will be used in part 2.
So here are the member variables used:
public bool generateContinuosly = false;  
public bool generateCollider = false;  
[Range(0.1f,50.0f)]  
public float yScaling = 5.0f; 
[Range(0.1f,20.0f)]  
public float detailScaling = 1.0f;  
[HideInInspector]  
public Vector3[] vertices;  
private Mesh mesh;  
Nothing fancy going on, just declaring some variables. The '[ Range( float , float ) ]' is an attribute used to show in the inspector a slider with the values defined in the parameters.
And the '[ HideInInspector ]' attribute prevents public fields from being shown in the inspector.
void Start()  
{  
   mesh = GetComponent<MeshFilter>().mesh;  
   vertices = mesh.vertices;  
}  
void Update()  
{  
   GenerateSurface();  
}  
Nothing fancy in the Start & Update functions either.
Now we will look at the 'GenerateSurface' function.
 void GenerateSurface()  
 {  
    vertices = mesh.vertices;  
    int counter = 0;   
    for (int i = 0; i < 11; i++)  
    {  
      for (int j = 0; j < 11; j++)  
      {  
        MeshCalculate(counter, i);
        counter++;  
      }  
    }  
    mesh.vertices = vertices;  
    mesh.RecalculateBounds();  
    mesh.RecalculateNormals();  
    if (generateCollider)  
    {  
       Destroy(GetComponent<MeshCollider>());  
       MeshCollider collider = gameObject.AddComponent<MeshCollider>();  
       collider.sharedMesh = null;  
       collider.sharedMesh = mesh;  
    }  
}  
Now we will look at the important stuff
MeshCalculate(counter, i); 
There will be a function called 'MeshCalculate' that takes in the index of the current vertex and the current row of that vertex (basically it's vertical offset, keep in mind this is in object space and therefore vertical does not actually mean up-down in world space, but in model/object space it is) and performs a certain set of actions which will modify the vertices of the mesh in some way.
mesh.RecalculateBounds();  
Recaculate bounds takes up the entire set of vertices and makes a box which encloses all those points.
We have to do this inorder to make sure the bounding volume is correct.
collider.sharedMesh = null;  
collider.sharedMesh = mesh;  
sharedMesh takes the 'mesh' object used for collision detection.
we are just setting it to the updated mesh after setting the previous one to null ( not necessary ) to help with garbage collection.
void MeshCalculate(int vertexIndex, int yOffset)  
{  
  if(generateContinuously)  
  {        
     vertices[vertexIndex].z = Mathf.PerlinNoise  
         (Time.time + (vertices[vertexIndex].x + transform.position.x) / detailScaling,  
          Time.time + (vertices[vertexIndex].y + transform.position.y)) * yScaling;  
       vertices[vertexIndex].z -= yOffset;  
  }  
  else  
  {  
     vertices[vertexIndex].z = Mathf.PerlinNoise  
        ((vertices[vertexIndex].x + transform.position.x) / detailScaling,  
        (vertices[vertexIndex].y + transform.position.y)) * yScaling;  
     vertices[vertexIndex].z -= yOffset;  
  }  
}  
This function basically uses Perlin Noise to generate those up and down waves/hills.
vertices[vertexIndex].z -= yOffset;  
we have this line to prevent all the vertices from bunching up and just forming a single line of vertices.
if(generateContinuously)  
{        
   vertices[vertexIndex].z = Mathf.PerlinNoise  
       (Time.time + (vertices[vertexIndex].x + transform.position.x) / detailScaling,  
        Time.time + (vertices[vertexIndex].y + transform.position.y)) * yScaling;  
   vertices[vertexIndex].z -= yOffset;  
}  
If the 'generateContinuosly' bool is true then it uses the Time.time value to give the seed value to the perlin noise function.
If  'generateContinuosly' is false the only factor acting as the seed to the perlin noise is the position of each individual vertex as well as the position of the object in world space.
Source code for Part 1 is available HERE.
Goto Part 2 for the rest of the tutorial, source code and unitypackage (contains everything).😀.
For more Unity development tutorials go HERE.
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If you have any questions that you might have about shaders or unity development in general don't be shy and leave a message on my facebook page or down in the comments.

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