Optimizing Voxel-Based Terrain Generation With Compute Shaders

Introduction

Voxel-based terrain generation is a popular method for creating realistic and diverse landscapes in games and simulations. By representing terrain as a three-dimensional grid of regular cubes, or voxels, developers can create complex landscapes with intricate details. However, generating terrain at runtime can be computationally expensive and slow, especially when you require large landscapes with rich detail. Compute shaders can help you optimize terrain generation processes using parallel computation on the GPU.

In this blog post, we will explore these topics:

• What are compute shaders?
• Generating voxel terrain using compute shaders
• Optimizing terrain generation with frustum culling

We'll be using the Unity game engine and the High-Level Shading Language (HLSL) for our examples.

What are Compute Shaders?

Compute shaders are a modern graphics programming feature that allows developers to perform computations on the GPU. This is advantageous because the GPU is designed for parallel processing, making it much more efficient at processing large quantities of data than the CPU. By offloading complex operations from the CPU to the GPU, compute shaders can improve performance.

#pragma kernel TerrainGeneration

RWTexture3D<float> _VoxelTexture;

[numthreads(8, 8, 1)]
void TerrainGeneration(uint3 id : SV_DispatchThreadID)
{
    // Perform voxel terrain generation
}

This example defines a simple compute shader with a kernel named TerrainGeneration. The numthreads attribute specifies the size of thread groups dispatched to this kernel. This example uses groups of 8x8x1 threads for a total of 64 threads per group.

Generating Voxel Terrain using Compute Shaders

To generate voxel terrain with a compute shader, we'll first create a 3D texture to store the terrain data. Then, we'll dispatch the shader to populate the texture with voxel information.

using UnityEngine;

public class VoxelGenerator : MonoBehaviour
{
    public ComputeShader TerrainShader;
    public int TerrainSize = 256;

    void Start()
    {
        // Creates a 3D texture to store voxel data
        RenderTexture voxelTexture = new RenderTexture(TerrainSize, TerrainSize, 0, RenderTextureFormat.ARGB32, 0);
        voxelTexture.dimension = UnityEngine.Rendering.TextureDimension.Tex3D;
        voxelTexture.enableRandomWrite = true;
        voxelTexture.Create();

        // Sets the compute shader parameters and dispatches it
        int kernel = TerrainShader.FindKernel("TerrainGeneration");
        TerrainShader.SetTexture(kernel, "_VoxelTexture", voxelTexture);
        TerrainShader.Dispatch(kernel, Mathf.CeilToInt(TerrainSize / 8f), Mathf.CeilToInt(TerrainSize / 8f), 1);

        // Apply the generated terrain data to the actual terrain mesh
        ProcessGeneratedTerrain(voxelTexture);
    }

    void ProcessGeneratedTerrain(RenderTexture voxelTexture)
    {
        // Processing the generated terrain's data, e.g. building meshes
    }
}

This C# script defines a basic voxel generator for Unity. The VoxelGenerator component utilizes a compute shader to generate voxel terrain data and store it in a 3D texture.

Optimizing Terrain Generation with Frustum Culling

Frustum culling is a technique used in rendering to remove objects outside the view of the camera's frustum. By only rendering the visible parts of the terrain, we can save performance by reducing the number of GPU operations.

Add frustum culling to the process by passing the frustum planes' equations to the compute shader.

void Start()
{
    // ...

    // Pass in frustum plane equations to compute shader
    Plane[] frustumPlanes = GeometryUtility.CalculateFrustumPlanes(Camera.main);
    Vector4[] planeEquations = new Vector4[6];
    for (int i = 0; i < 6; i++)
    {
        planeEquations[i] = new Vector4(frustumPlanes[i].normal.x, frustumPlanes[i].normal.y, frustumPlanes[i].normal.z, frustumPlanes[i].distance);
    }
    TerrainShader.SetVectorArray("_FrustumPlanes", planeEquations);

    // ...
}

In the compute shader, check whether each voxel lies outside any camera frustum planes. If a voxel isn't visible, skip processing it.

#pragma kernel TerrainGeneration

RWTexture3D<float> _VoxelTexture;
float4 _FrustumPlanes[6];

[numthreads(8, 8, 1)]
void TerrainGeneration(uint3 id : SV_DispatchThreadID)
{
    float3 voxelPosition = float3(id) / TerrainSize;

    // Check if voxel is inside the camera frustum
    bool insideFrustum = true;
    for (int i = 0; i < 6; i++)
    {
        if (dot(_FrustumPlanes[i].xyz, voxelPosition) + _FrustumPlanes[i].w < 0)
        {
            insideFrustum = false;
            break;
        }
    }

    // If voxel is not inside the frustum, skip processing
    if (!insideFrustum)
    {
        return;
    }

    // Perform voxel terrain generation
    // ...
}

By implementing frustum culling in our example, the terrain generation process only covers visible parts, resulting in improved performance.

Conclusion

Compute shaders offer a powerful way of optimizing voxel-based terrain generation in modern games and simulations. By offloading terrain generation to the GPU and applying additional optimizations such as frustum culling, developers can create large-scale, high-detail environments without compromising performance.