Unity uses mesh to realize real-time point cloud (II)

One 、 background

In the last one , We implemented static point cloud , And try directly in CPU The efficiency of point cloud discovery is very low . So this article , We will update the point cloud on ComputeShader in .

Two 、 Ideas

1. Or custom mesh Create a point cloud model
2. The vertex coordinates and colors in the point cloud model are ComputeShader Assignment in
3. Customize UnlitShader In order to get ComputeShader Render the vertex coordinates and colors calculated in

3、 ... and 、 Realization

Customize mesh

By default , In a mesh At most, we can define 65535 vertices , If there are more vertices, we need to modify a parameter .Unity - Scripting API: IndexFormat (unity3d.com)

Let's create an empty game object , Then add MeshFilter and MeshRender Components . Then create a new script , This script is used to initialize the point cloud mesh Of .

[RequireComponent(typeof(MeshFilter), typeof(MeshRenderer))]
public class PointCloud : MonoBehaviour
{
    
    public const int Width = 640, Height = 480;

    private Vector3[] positions;
    private int[] indices;
    private Color[] colors;
    private Mesh mesh;
    // Use this for initialization
    void Start()
    {
    
        var totalPointNum = Width * Height;
        positions = new Vector3[totalPointNum];
        indices = new int[totalPointNum];
        colors = new Color[totalPointNum];
        for (int i = 0; i < totalPointNum; i++)
        {
    
            positions[i] = new Vector3(0, 0, 0);
            indices[i] = i;
            colors[i] = Color.red;
        }
        mesh = GetComponent<MeshFilter>().mesh;
        mesh.indexFormat = UnityEngine.Rendering.IndexFormat.UInt32;
        mesh.vertices = positions;
        mesh.colors = colors;
        mesh.SetIndices(indices, MeshTopology.Points, 0);
    }
}

mesh After defining it, we need to Render Shader Reassign the coordinates and colors of vertices in , This is a dynamic point cloud .

RenderShader

Shader "Unlit/PointCloudS"
{
	Properties
	{
		
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }
		LOD 100

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#include "UnityCG.cginc"

			struct v2f
            {
                float4 col : COLOR0;
                float4 vertex : SV_POSITION;
            };
            
            struct PointCloudData
            {
		        float3 pos;
		        float4 col;
            };
 
            StructuredBuffer<PointCloudData> PointCloudDataBuffer;
            
            v2f vert (uint id : SV_VertexID)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(float4(PointCloudDataBuffer[id].pos, 1));
                o.col = PointCloudDataBuffer[id].col;
                return o;
            }
 
            fixed4 frag (v2f i) : SV_Target
            {
                return i.col;
            }
			ENDCG
		}
	}
}

The more important thing is ：

• Here we customize the coordinates and color data types of the point cloud top points , Also created corresponding buffer Used to receive data passed in by users .
• Vertex function （vert） The parameter in uses vertex index , So that we can buffer The corresponding data is found in

For convenience , Let's separate the structure .

Shader "Unlit/PointCloudS"
{
	Properties
	{
		
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }
		LOD 100

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#include "UnityCG.cginc"

			struct v2f
            {
                float4 col : COLOR0;
                float4 vertex : SV_POSITION;
            };

            StructuredBuffer<float3> PointPos;
            StructuredBuffer<float4> PointCol;
            
            v2f vert (uint id : SV_VertexID)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(float4(PointPos[id], 1));
                o.col = PointCol[id];
                return o;
            }
 
            fixed4 frag (v2f i) : SV_Target
            {
                return i.col;
            }
			ENDCG
		}
	}
}

So here's the problem , We are Shader As defined in buffer How to get the data of ？？？

to Buffer assignment

We know , Can pass Material Directly to the corresponding Shader Parameter assignment in .Unity Shader（ to Shader Passing user data ）_ The goal is ：MVP-CSDN Blog

public class PointCloudCSHelper : MonoBehaviour
{
    
    public Material material;

    ComputeBuffer pointPosBuffer;
    ComputeBuffer pointColBuffer;
    int PointCloudPotNum {
     get {
     return PointCloud.Width * PointCloud.Height; } }

    void Start()
    {
    
        pointPosBuffer = new ComputeBuffer(PointCloudPotNum, 12);
        material.SetBuffer("PointPos", pointPosBuffer);

        pointColBuffer = new ComputeBuffer(PointCloudPotNum, 16);
        material.SetBuffer("PointCol", pointColBuffer);

        StartCoroutine(UpdatePointCloudData());
    }

    IEnumerator UpdatePointCloudData()
    {
    
        while (true)
        {
    
            // Simulation point cloud data update , Of course, this way will occupy CPU.
            Vector3[] pos = GetPositionsFromCsv(@"D:\SIF2610-Demo-Kits-DX-PreV1.06.210901\SnapShots\20210904\1145146883\PointCloud.csv");
            Color[] colors = GetColors(PointCloudPotNum);

            pointPosBuffer.SetData(pos);
            pointColBuffer.SetData(colors);
            yield return new WaitForSeconds(1);
        }
    }

    void OnDestroy()
    {
    
        pointPosBuffer.Release();
        pointPosBuffer.Dispose();

        pointColBuffer.Release();
        pointColBuffer.Dispose();
    }

    Vector3[] GetPositionsFromCsv(string path)
    {
    
        List<Vector3> pos = new List<Vector3>();
        using (StreamReader sr = new StreamReader(path))
        {
    
            while (!sr.EndOfStream)
            {
    
                var positions = sr.ReadLine().Split(',');

                pos.Add(new Vector3(float.Parse(positions[0]), float.Parse(positions[1]), float.Parse(positions[2])));
            }
        }

        return pos.ToArray();
    }

    private Color[] GetColors(int num)
    {
    
        Color[] colors = new Color[num];
        for (int i = 0; i < colors.Length; i++)
        {
    
            colors[i] = UnityEngine.Random.ColorHSV();
        }

        return colors;
    }
}

The code structure should also be very simple , Is to define first ComputeBuffer Then bind to Render Shader As stated in buffer, Finally, give buffer Assignment so Render Shader The value in will also be updated , Then the coordinates and colors of the vertices will also be updated .

But in the above example code , We updated some point cloud coordinates and colors randomly , This one will take up a little CPU. But in the actual project , We usually get coordinates and color data directly . But there will also be problems that you can't get coordinates or color data directly , We may need to make a simple calculation , But generally, the amount of point cloud data is relatively large , Even simple calculations will take up a lot CPU, So we can put it in GPU Middle computation , That is to say ComputeShader.

ComputeShader Computing big data

About ComputeShader You can see the introduction here ：ComputeShader_ The goal is ：MVP-CSDN Blog

// Each #kernel tells which function to compile; you can have many kernels
#pragma kernel UpdatePointCloud

// Create a RenderTexture with enableRandomWrite flag and set it
// with cs.SetTexture

RWStructuredBuffer<float3> PointPos;
RWStructuredBuffer<float4> PointCol;
float Time;
 
[numthreads(8,8,1)]
void UpdatePointCloud (uint3 gid : SV_GroupID, uint index : SV_GroupIndex)
{
     int pindex = gid.x *8*8*1 + index;
     PointPos[pindex]=float3(pindex/1000.0-50+ sin(Time) , 20 * cos(pindex)+10*sin(Time), 20 * sin(pindex)+10*sin(Time));
     PointCol[pindex]=float4((sin(Time) + 1)*0.5, (cos(Time) + 1)*0.5, abs(cos(Time) + sin(Time)), 1);
}

alike , We also applied for some here buffer, these buffer Used to receive from CPU Data coming in , Then do some simple calculations to get the final data .

public class PointCloudCSHelper : MonoBehaviour
{
    
    public ComputeShader shader;
    public Material material;

    ComputeBuffer pointPosBuffer;
    ComputeBuffer pointColBuffer;
    int PointCloudPotNum {
     get {
     return PointCloud.Width * PointCloud.Height; } }
    int kernel;
    uint x, y, z;
    void Start()
    {
    
        kernel = shader.FindKernel("UpdatePointCloud");

        pointPosBuffer = new ComputeBuffer(PointCloudPotNum, 12);
        shader.SetBuffer(kernel, "PointPos", pointPosBuffer);
        material.SetBuffer("PointPos", pointPosBuffer);

        pointColBuffer = new ComputeBuffer(PointCloudPotNum, 16);
        shader.SetBuffer(kernel, "PointCol", pointColBuffer);
        material.SetBuffer("PointCol", pointColBuffer);

        shader.GetKernelThreadGroupSizes(kernel, out x, out y, out z);

        StartCoroutine(UpdatePointCloudData());
    }

    IEnumerator UpdatePointCloudData()
    {
    
        while (true)
        {
    
            shader.SetFloat("Time", Time.time);
            shader.Dispatch(kernel, (int)(PointCloudPotNum / (x * y * z)), 1, 1);
            yield return new WaitForSeconds(1);
        }
    }

    void OnDestroy()
    {
    
        pointPosBuffer.Release();
        pointPosBuffer.Dispose();

        pointColBuffer.Release();
        pointColBuffer.Dispose();
    }
}

Here we will define ComputeBuffer Also related to ComputeShader in , Be careful ,RenderShader and ComputeShader Medium buffer Is the same , This buffer The value of is in ComputeShader Calculated in , then RenderShader Just call , Every update is also executed ComputeShader that will do , Re pass the value that needs to be updated GPU Calculate again in .

public class PointCloudCSHelper : MonoBehaviour
{
    
    public ComputeShader shader;
    public Material material;

    ComputeBuffer pointPosBuffer;
    ComputeBuffer pointColBuffer;
    int PointCloudPotNum {
     get {
     return PointCloud.Width * PointCloud.Height; } }
    int kernel;
    uint x, y, z;
    void Start()
    {
    
        kernel = shader.FindKernel("UpdatePointCloud");

        pointPosBuffer = new ComputeBuffer(PointCloudPotNum, 12);
        shader.SetBuffer(kernel, "PointPos", pointPosBuffer);
        material.SetBuffer("PointPos", pointPosBuffer);

        pointColBuffer = new ComputeBuffer(PointCloudPotNum, 16);
        shader.SetBuffer(kernel, "PointCol", pointColBuffer);
        material.SetBuffer("PointCol", pointColBuffer);

        shader.GetKernelThreadGroupSizes(kernel, out x, out y, out z);

        StartCoroutine(UpdatePointCloudData());
    }

    IEnumerator UpdatePointCloudData()
    {
    
        while (true)
        {
    
            shader.SetFloat("Time", Time.time);
            shader.Dispatch(kernel, (int)(PointCloudPotNum / (x * y * z)), 1, 1);
            yield return new WaitForSeconds(1);
        }
    }
    
    void OnDestroy()
    {
    
        pointPosBuffer.Release();
        pointPosBuffer.Dispose();

        pointColBuffer.Release();
        pointColBuffer.Dispose();
    }
}

effect

Project code ：heater404/PointCloud (github.com)

To be done ：

1、 Point cloud translation and rotation