ThomagicRenderer/Runtime/Scripts/BillboardDrawCall.cs

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

namespace Assets.ThoMagic.Renderer
{
    public class BillboardDrawCall : DrawCall
    {
        private static Mesh _billboardMesh;

        private static Mesh GetBillboardMesh()
        {
            if (_billboardMesh == null)
            {
                _billboardMesh = new Mesh();
                _billboardMesh.name = "Billboard Mesh";
                _billboardMesh.vertices = new Vector3[6];
                _billboardMesh.triangles = new int[6] {
                    0,
                    1,
                    2,
                    3,
                    4,
                    5
                };

                _billboardMesh.SetUVs(0,new Vector2[6]
                {
                      new Vector2(0.0f, 0.0f),
                      new Vector2(0.0f, 1f),
                      new Vector2(1f, 1f),
                      new Vector2(0.0f, 0.0f),
                      new Vector2(1f, 1f),
                      new Vector2(1f, 0.0f)
                });

                _billboardMesh.SetUVs(1, new Vector4[6]
                {
                  new Vector4(1f, 1f, 0.0f, 0.0f),
                  new Vector4(1f, 1f, 0.0f, 0.0f),
                  new Vector4(1f, 1f, 0.0f, 0.0f),
                  new Vector4(1f, 1f, 0.0f, 0.0f),
                  new Vector4(1f, 1f, 0.0f, 0.0f),
                  new Vector4(1f, 1f, 0.0f, 0.0f)
                });
                
                _billboardMesh.UploadMeshData(true);
            }

            return _billboardMesh;
        }

        public BillboardDrawCall(
            int lodNr,
            BillboardAsset billboardAsset,
            Material material,
            Matrix4x4 localToWorldMatrix,
            uint baseIndirectArgsIndex,
            List<GraphicsBuffer.IndirectDrawIndexedArgs> indirectDrawIndexedArgs,
            in RenderParams renderParams)
          : base(lodNr, 
                GetBillboardMesh(), 
                new Material[1]{ material }, 
                localToWorldMatrix, 
                baseIndirectArgsIndex,
                indirectDrawIndexedArgs,
                in renderParams)
        {
            if (billboardAsset == null)
                throw new ArgumentNullException(nameof(billboardAsset));

            SetBillboardPerBatch(billboardAsset);
        }

        internal override void Dispose() {
            UnityEngine.Object.Destroy(_billboardMesh);
            base.Dispose();
        }       

        public override void Draw(Camera camera, ObjectData obj, GraphicsBuffer indirectDrawIndexedArgs)
        {
            SetBillboardPerCamera(camera);
            base.Draw(camera, obj, indirectDrawIndexedArgs);
        }

        private void SetBillboardPerCamera(Camera camera)
        {
            Vector3 position = camera.transform.position;
            Vector3 vector3_1 = camera.transform.forward * -1f;
            vector3_1.y = 0.0f;
            vector3_1.Normalize();
            Vector3 vector3_2 = camera.transform.right * -1f;
            vector3_2.y = 0.0f;
            vector3_2.Normalize();
            float num1 = Mathf.Atan2(vector3_1.z, vector3_1.x);
            float num2 = num1 + (num1 < 0.0f ? 6.283185f : 0.0f);
            Vector4 vector4;
            vector4.x = position.x;
            vector4.y = position.y;
            vector4.z = position.z;
            vector4.w = num2;
            for (int index = 0; index < RenderParams.Length; ++index)
            {
                RenderParams[index].matProps.SetVector("unity_BillboardNormal", vector3_1);
                RenderParams[index].matProps.SetVector("unity_BillboardTangent", vector3_2);
                RenderParams[index].matProps.SetVector("unity_BillboardCameraParams", vector4);
            }
        }

        private void SetBillboardPerBatch(BillboardAsset asset)
        {
            Vector4 vector4_1 = Vector4.zero;
            vector4_1.x = asset.imageCount;
            vector4_1.y = 1.0f / (6.28318548202515f / asset.imageCount);
            Vector4 vector4_2 = Vector4.zero;
            vector4_2.x = asset.width;
            vector4_2.y = asset.height;
            vector4_2.z = asset.bottom;
            Vector4[] imageTexCoords = asset.GetImageTexCoords();
            for (int index = 0; index < RenderParams.Length; ++index)
            {
                RenderParams[index].matProps.SetVector("unity_BillboardInfo", vector4_1);
                RenderParams[index].matProps.SetVector("unity_BillboardSize", vector4_2);
                RenderParams[index].matProps.SetVectorArray("unity_BillboardImageTexCoords", imageTexCoords);
            }
        }
    }
}