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

public class Grass : MonoBehaviour
{
    public Mesh mesh;
    public Material material;
    public Bounds bounds;
    public float scaleMult;
    public ShadowCastingMode shadowCastingMode;
    public bool isReceiveShadow;



    public Vector3 objectBoundMin;
    public Vector3 objectBoundMax;
    public ComputeShader computeShader;
    int kernel = 0;
    ComputeBuffer instDataBuffer;
    ComputeBuffer cullIDsBuffer;
    ComputeBuffer argsBuffer;

    public Transform root;
    List<InstData> dataInfors = new List<InstData>();


    private struct InstData
    {
        public Vector3 pos;
        public Vector3 angle;
        public Vector3 scale;

        //
        public static int GetNum()
        {
            return sizeof(float) * 3 + sizeof(float) * 3 + sizeof(float) * 3;
        }
    }














    private void Start()
    {
        GetDataInfors();
        InitializeBuffers();
    }

    void GetDataInfors()
    {
        foreach (Transform t in root.GetComponentInChildren<Transform>())
        {
            InstData instData = new InstData();
            instData.pos = t.position;
            instData.angle = t.eulerAngles;
            instData.scale = t.localScale * scaleMult;
            dataInfors.Add(instData);

            //
            t.gameObject.SetActive(false);
        }
    }

    private void InitializeBuffers()
    {
        // Arguments for drawing mesh.
        uint[] args = new uint[5] { 0, 0, 0, 0, 0 };
        // 0 == number of triangle indices, 1 == count, others are only relevant if drawing submeshes.
        args[0] = (uint)mesh.GetIndexCount(0);
        args[1] = (uint)dataInfors.Count;
        args[2] = (uint)mesh.GetIndexStart(0);
        args[3] = (uint)mesh.GetBaseVertex(0);
        argsBuffer = new ComputeBuffer(1, args.Length * sizeof(uint), ComputeBufferType.IndirectArguments);
        argsBuffer.SetData(args);

        // Initialize buffer with the given population.
        material = Instantiate(material);
        instDataBuffer = new ComputeBuffer(dataInfors.Count, InstData.GetNum());
        instDataBuffer.SetData(dataInfors);
        material.SetBuffer("_InstDataBuffer", instDataBuffer);
        cullIDsBuffer = new ComputeBuffer(dataInfors.Count, sizeof(uint), ComputeBufferType.Append);
        material.SetBuffer("_CullIDsBuffer", cullIDsBuffer);

        //
        computeShader = Instantiate(computeShader);
        kernel = computeShader.FindKernel("CSMain");
        computeShader.SetBuffer(kernel, "_InstDataBuffer", instDataBuffer);
        computeShader.SetVector("_BoundMin", objectBoundMin);
        computeShader.SetVector("_BoundMax", objectBoundMax);
        computeShader.SetBuffer(kernel, "_CullIDsBuffer", cullIDsBuffer);
    }















    private void Update()
    {
        cullIDsBuffer.SetCounterValue(0);
        computeShader.SetVectorArray("_FrustumPlanes", GpuCullCamera.inst.frustumPlanes);
        computeShader.Dispatch(kernel, Mathf.CeilToInt(dataInfors.Count / 128f), 1, 1);
        ComputeBuffer.CopyCount(cullIDsBuffer, argsBuffer, sizeof(uint));

        //
        Graphics.DrawMeshInstancedIndirect(mesh, 0, material, bounds, argsBuffer, 0, null, shadowCastingMode, isReceiveShadow, LayerMask.NameToLayer("Instance"));
    }

    private void OnDrawGizmos()
    {
        Gizmos.color = Color.blue;
        Gizmos.DrawWireCube(bounds.center, bounds.size);
    }

    private void OnDisable()
    {
        // Release gracefully.
        if (instDataBuffer != null)
        {
            instDataBuffer.Release();
        }
        instDataBuffer = null;

        if (cullIDsBuffer != null)
        {
            cullIDsBuffer.Release();
        }
        cullIDsBuffer = null;

        if (argsBuffer != null)
        {
            argsBuffer.Release();
        }
        argsBuffer = null;
    }
}