using UnityEngine;
[ExecuteInEditMode]
public class Note7Main : MonoBehaviour
{
    public Mesh mesh;
    public Material material;
    
    int instanceCount = 200;
    Bounds instanceBounds;
    ComputeBuffer bufferWithArgs = null;
    ComputeBuffer instanceParamBufferData = null;
    
    // Start is called before the first frame update
    void Start()
    {
        instanceBounds = new Bounds(new Vector3(0, 0, 0), new Vector3(100, 100, 100));
        uint[] args = new uint[5] { 0, 0, 0, 0, 0 };
        bufferWithArgs = new ComputeBuffer(1, args.Length * sizeof(uint), ComputeBufferType.IndirectArguments);
        int subMeshIndex = 0;
        args[0] = mesh.GetIndexCount(subMeshIndex);
        args[1] = (uint)instanceCount;
        args[2] = mesh.GetIndexStart(subMeshIndex);
        args[3] = mesh.GetBaseVertex(subMeshIndex);
        bufferWithArgs.SetData(args);
        InstanceParam[] instanceParam = new InstanceParam[instanceCount];
        for (int i = 0; i < instanceCount; i++)
        {
            Vector3 position = Random.insideUnitSphere * 5;
            Quaternion q = Quaternion.Euler(Random.Range(0.0f, 90.0f), Random.Range(0.0f, 90.0f), Random.Range(0.0f, 90.0f));
            float s = Random.value;
            Vector3 scale = new Vector3(s, s, s);
            instanceParam[i].instanceToObjectMatrix = Matrix4x4.TRS(position, q, scale);
            instanceParam[i].color = Random.ColorHSV();
        }
        int stride = System.Runtime.InteropServices.Marshal.SizeOf(typeof(InstanceParam));
        instanceParamBufferData = new ComputeBuffer(instanceCount, stride);
        instanceParamBufferData.SetData(instanceParam);
        material.SetBuffer("dataBuffer", instanceParamBufferData);
        material.SetMatrix("ObjectToWorld", Matrix4x4.identity);
    }
    // Update is called once per frame
    void Update()
    {
        if (bufferWithArgs != null)
        {
            Graphics.DrawMeshInstancedIndirect(mesh, 0, material, instanceBounds, bufferWithArgs, 0);
        }
    }
    private void OnDestroy()
    {
        if (bufferWithArgs != null)
        {
            bufferWithArgs.Release();
        }
        if (instanceParamBufferData != null)
        {
            instanceParamBufferData.Release();
        }
    }
}

Shader "Custom/SimpleSurfaceIntanceShader"
{
    Properties
    {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Metallic ("Metallic", Range(0,1)) = 0.0
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 200
        CGPROGRAM
        // Physically based Standard lighting model, and enable shadows on all light types
        #pragma surface surf Standard fullforwardshadows
    #pragma target 4.5
    #pragma multi_compile_instancing
        #pragma instancing_options procedural:setup     
        
    struct InstanceParam
    {     
      float4 color;
      float4x4 instanceToObjectMatrix;
    };
  #ifdef UNITY_PROCEDURAL_INSTANCING_ENABLED
        StructuredBuffer<InstanceParam> dataBuffer;
    #endif
    float4x4 ObjectToWorld;
  
        sampler2D _MainTex;
        struct Input
        {
            float2 uv_MainTex;
        };
        half _Glossiness;
        half _Metallic;
        fixed4 _Color;
    void setup()
        {
        #ifdef UNITY_PROCEDURAL_INSTANCING_ENABLED
            InstanceParam data = dataBuffer[unity_InstanceID];
            unity_ObjectToWorld = mul(ObjectToWorld, data.instanceToObjectMatrix);        
        #endif
        }
        void surf (Input IN, inout SurfaceOutputStandard o)
        {
            // Albedo comes from a texture tinted by color
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;    
            o.Albedo = c.rgb;
            // Metallic and smoothness come from slider variables
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = c.a;
        }
        ENDCG
    }
    FallBack "Diffuse"
}