Unity3D学习笔记7——GPU实例化(2)
1. 概述
在上一篇文章《Unity3D学习笔记6——GPU实例化(1)》详细介绍了Unity3d中GPU实例化的实现，并且给出了详细代码。不过其着色器实现是简单的顶点+片元着色器实现的。Unity提供的很多着色器是表面着色器，通过表面着色器，也是可以实现GPU实例化的。
2. 详论
2.1. 实现
首先，我们还是挂接与上篇文章一样的脚本：
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();
}
}
}
不过，脚本的材质设置需要使用我们新的材质：
这个材质可以通过使用Standard Surface Shader作为我们修改的模板：
修改后的着色器代码如下：
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"
}
最后的显示效果如下：
2.2. 解析
对比修改之前的着色器代码：
#pragma multi_compile_instancing的意思是给这个着色器增加了实例化的变体，也就是增加了诸如INSTANCING_ON PROCEDURAL_ON这样的关键字，可以编译实例化的着色器版本。#pragma instancing_options procedural:setup是搭配Graphics.DrawMeshInstancedIndirect使用的，在顶点着色器阶段开始时，Unity会调用冒号后指定的setup()函数。- setup()函数的意思是通过实例化Id也就是unity_InstanceID，找到正确的实例化数据，并且调整Unity的内置变量unity_ObjectToWorld——也就是模型矩阵。正如上一篇文章所言，GPU实例化的关键就在于模型矩阵的重新计算。在Unity API官方示例中，还修改了其逆矩阵unity_WorldToObject。
