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Terrain Mesh Generation

Generating terrain meshes programmatically is the first step toward building procedural worlds. Instead of hand-modeling a landscape, we generate a grid of vertices and “displace” them using a heightmap or noise.

1. The Grid Structure

A terrain mesh is a 2D grid of vertices. For a $10 \times 10$ terrain “quad,” we need $11 \times 11$ vertices to close the loops.

• Vertices: Each vertex has a position $(x, y, z)$. The $y$ component is the height.
• UVs: Standard $(0..1)$ coordinates used for the splatmap and detail texturing.
• Triangles: Every grid square (quad) is split into two triangles (e.g., indices [0, 1, 11] and [1, 12, 11]).

2. Displacement (Height)

The $y$ value of each vertex is determined by:

1. Heightmaps: Grayscale textures where Black = Valley and White = Peak.
2. Noise Functions: Using Perlin or Simplex noise allows for infinite, deterministic terrain generation.

3. Implementation (C# Example)

void CreateMesh() {
    vertices = new Vector3[(xSize + 1) * (zSize + 1)];
    for (int i = 0, z = 0; z <= zSize; z++) {
        for (int x = 0; x <= xSize; x++) {
            float y = Mathf.PerlinNoise(x * .3f, z * .3f) * 2f;
            vertices[i] = new Vector3(x, y, z);
            i++;
        }
    }
    // ... Triangle and Normal generation ...
}

4. Calculating Normals

Lighting requires accurate surface normals. For procedural terrain, don’t rely on the engine’s default calculator.

• Neighbor Sampling: For a vertex at $(x, z)$, sample the height at $(x+1, z)$ and $(x, z+1)$.
• Cross Product: The cross product of the vectors pointing to those neighbors gives you the exact normal for that point on the terrain.

5. Performance: Chunking & LOD

Rendering a massive $4096 \times 4096$ grid as a single mesh will kill performance.

• Chunking: Break the terrain into $32 \times 32$ or $64 \times 64$ “Chunks.”
• Culling: Only render chunks inside the camera frustum.
• LOD (Level of Detail): Faraway chunks should use a lower resolution (fewer vertices) to save GPU cycles.