VertexBufferVisualizer

readme.md

【Unity】MeshのVertexBufferをComputeShaderで扱うMinimal Sample

参考資料

Unityの新MeshAPIでMeshColliderをリアルタイム変形させる
Unity 21.2 Mesh API Compute Shader Access

VertexBufferVisualizer.compute

#pragma kernel CSMain

struct VertexPosition
{
    float3 Position;
};

ByteAddressBuffer Verts;
RWStructuredBuffer<VertexPosition> VertexPositionBuffer;;

float4x4 LocalToWorld;
int VertexCount;

[numthreads(1,1,1)]
void CSMain (uint3 id : SV_GroupThreadID)
{
    for(int i = 0; i < VertexCount; i++)
    {
        //float3 Position, float3 Normal, float4 Tangent, float2 TexCoord0
        //total 12 floats, 4bytes
        //4 * 12 = 48
        int vidx = i.x * 48;
        uint3 praw = Verts.Load3(vidx);
        float3 localPosition = asfloat(praw);
        float4 worldPosition = mul(LocalToWorld, float4(localPosition, 1));
        VertexPositionBuffer[i].Position = float3(worldPosition.xyz);
    }
}

VertexBufferVisualizer.cs

using System.Collections.Generic;
using System.Runtime.InteropServices;
using UnityEngine;
using UnityEngine.Rendering;

public class VertexBufferVisualizer : MonoBehaviour
{
    [SerializeField]
    private GameObject _meshObject;

    [SerializeField]
    private ComputeShader _computeShader;
    
    private ComputeBuffer _vertexPositionBuffer;
    private GraphicsBuffer _vertexBuffer;
    private VertexPosition[] _result;
    private Mesh _mesh;
    private List<GameObject> _vertVisualiser = new List<GameObject>();

    public struct VertexPosition
    {
        public Vector3 Position;
    }
    
    void Start()
    {
        _mesh = _meshObject.GetComponent<MeshFilter>().mesh;

        VertexAttributeDescriptor[] attrubtes = _mesh.GetVertexAttributes();
        //Position Float32 0 30 0 48 
        //Normal Float32 0 312 0 48 
        //Tangent Float32 0 424 0 48 
        //TexCoord0 Float32 0 240 0 48 
        for (int i = 0; i < attrubtes.Length; i++)
        {
            Debug.Log($"{attrubtes[i].attribute} " +
                      $"{attrubtes[i].format} " +
                      $"{attrubtes[i].stream} " +
                      $"{attrubtes[i].dimension}" +
                      $"{_mesh.GetVertexAttributeOffset(attrubtes[i].attribute)} " +
                      $"{_mesh.GetVertexAttributeStream(attrubtes[i].attribute)} " +
                      $"{_mesh.GetVertexBufferStride(attrubtes[i].stream)} ");
        }
        
        _vertexPositionBuffer = new ComputeBuffer(_mesh.vertexCount, Marshal.SizeOf<VertexPosition>());

        _mesh.vertexBufferTarget |= GraphicsBuffer.Target.Raw;
        _vertexBuffer = _mesh.GetVertexBuffer(0);
        _computeShader.SetBuffer(0, "Verts", _vertexBuffer);
        _computeShader.SetBuffer(0, "VertexPositionBuffer", _vertexPositionBuffer);
        _computeShader.SetInt("VertexCount", _mesh.vertexCount);

        _result = new VertexPosition[_mesh.vertexCount];
        
        for (int i = 0; i < _mesh.vertexCount; i++)
        {
            var sphere = GameObject.CreatePrimitive(PrimitiveType.Sphere);
            sphere.transform.localScale = Vector3.one * 0.1f;
            _vertVisualiser.Add(sphere);
        }
    }

    private void OnDestroy()
    {
        _vertexBuffer.Dispose();
        _vertexPositionBuffer.Dispose();
    }

    void Update()
    {
        _computeShader.SetMatrix("LocalToWorld", _meshObject.transform.localToWorldMatrix);
        _computeShader.Dispatch(0, 1,1,1);
        _vertexPositionBuffer.GetData(_result);
        for (int i = 0; i < _vertVisualiser.Count; i++)
        {
            _vertVisualiser[i].transform.position = _result[i].Position;
        }
    }
}