# Unity mesh only rendering one set of triangles

I've been using Unity3D to procedurally generate terrain with Perlin Noise and I've come across a problem where the mesh that I've constructed only renders one set of triangles.

The following is my MeshGeneration code:

using System.Collections;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using NUnit.Framework.Internal.Execution;
using UnityEngine;

public static class MeshGenerator
{
public static MeshData GenerateMesh(float[,] heightMap)
{
int height = heightMap.GetLength(0);
int width = heightMap.GetLength(1);
int vertexIndex = 0;

MeshData meshData = new MeshData(width, height);

for (int y = 0; y < height; y++)
{
for (int x = 0; x < width; x++)
{
meshData.vertices[vertexIndex] = new Vector3(x, heightMap[y, x], y);
meshData.uvs[vertexIndex] = new Vector2( x/(float)width, y/(float)height);

// If we are not on the edge, then add two triangles to the mesh
if ((x != width - 1) && (y != height - 1))
{
meshData.AddTriangle(
vertexIndex,
vertexIndex + width,
vertexIndex + width + 1
);
meshData.AddTriangle(
vertexIndex,
vertexIndex + 1,
vertexIndex + width + 1
);
}

vertexIndex++;
}
}

return meshData;
}
}

public class MeshData
{
public Vector3[] vertices;
public Vector2[] uvs;
public int[] triangles;

public int triangleIndex;
public MeshData(int meshWidth, int meshHeight)
{
vertices = new Vector3[meshWidth * meshHeight];
uvs = new Vector2[meshWidth * meshHeight];
triangles = new int[(meshWidth - 1) * (meshHeight - 1) * 6];
}

public void AddTriangle(int a, int b, int c)
{
triangles[triangleIndex] = a;
triangles[triangleIndex + 1] = b;
triangles[triangleIndex + 2] = c;
triangleIndex += 3;
}

public Mesh CreateMesh()
{
Mesh mesh = new Mesh();
mesh.vertices = this.vertices;
mesh.uv = this.uvs;
mesh.triangles = this.triangles;

mesh.RecalculateNormals();
return mesh;
}
}



I'm then passing in the mesh that I get from MeshData.CreateMesh() into the following function.

public void BuildMesh(MeshData meshData, Texture2D texture)
{
meshFilter.sharedMesh = meshData.CreateMesh();
meshRenderer.sharedMaterial.mainTexture = texture;
}


I'm following this tutorial: https://www.youtube.com/watch?v=4RpVBYW1r5M&list=PLFt_AvWsXl0eBW2EiBtl_sxmDtSgZBxB3&index=5

The Mesh generation code works by creating arrays of vertices, uvs, and triangles, and the populating them by iterating over a Vector3[] heightMap that I created with perlin noise.

## 1 Answer

Solved the problem myself. The remaining triangles were being generated on the other side of the mesh. This was I didn't know that the order of the vertices had to be in clockwise order.