毛发，无论是人类的头发、动物的皮毛，还是奇幻生物的绒毛，都是构成生命感和真实感不可或缺的元素。它对光线的独特散射、吸收和反射，赋予了物体柔软、蓬松、有生命力的质感。它不仅仅是让角色看起来更“毛茸茸”那么简单，更是通向极致真实感和视觉沉浸感的关键一步。本期我们来在Unity6的UDRP项目中实现一个Shell外壳技术的Fur毛发的基础版渲染效果，最终效果如下图所示。

[基础版包含纹理+Shell+AO+边缘光效果]

使用Unity版本：6000.0.43f1

我会先实现UDRP下单Pass(不应用GPUInstancing)+DrawMesh绘制API的方案，后面会再用GPUInstancing(分别使用两种实例绘制API)改进性能。

一.为什么不使用多Pass渲染

1.高DrawCall&打断SRPBatcher

在URP中，Pass由手动控制，一般在不开启GPU Instancing时，每个Pass都是一次DrawCall，且Shader内多Pass（大部分情况）会导致渲染状态的切换，导致SRP Batcher 无法合批，所以URP中提倡主Pass渲染。

2.RenderFeature实现难度大

可以使用RenderFeature虽然可以避开Shader内多pass，但是存在注入难度大 & 与多 Pass Shader 协调困难的问题。所以一般是利用RenderFeature插入额外效果，而不是实现Shader 多 Pass。

3.追求优良性能

多 Pass 意味着多次顶点变换、光照计算、纹理采样对草,毛发这样一组“重复结构”的对象很不划算，使用URP鼓励的主通道渲染配合GPUInstancing是性能最优的选择。

二.Shell基本原理

Shell算法可以说是很经典了，网上一搜有大量的介绍，下方的原理图就很直观了，这里我用白话总结一些关键点。

1.顶点沿法线偏移做多壳层

渲染多层壳(Shell,本质是把一个Mesh渲染多次)，根据壳层序号作为偏移算子，将顶点沿法线方向偏移一定距离。

2.壳层透明度递减做体积感

采样一张噪声纹理图(仅需读取单通道的黑白信息)，根据壳层序号与总壳数的比值，将则遮罩图的黑白信息应用到每层壳的透明通道，使外层壳透明度逐渐降低，从而形成多层的体积感。

使用到的毛发噪声及法线贴图：

三.3种Shell_Fur实现方式

我采用UnlitShader+C#控制脚本的形式实现。在Shader内部，我修改了默认的CGPROGRAM，使用HLSLPROGRAM，对应HLSL语法。

注意引入基本库

 #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

1.单通道(非GPUInstancing)+DrawMesh实现基础绘制

(1)Property声明

根据需求我定义了以下属性：

(1)基础Shell：定义了毛发噪声纹理, 毛发(壳层偏移)长度和壳层总数；

(1)AO：定义了毛发的根部颜色和末端颜色；

(2)边缘光：定义了边缘光颜色和菲涅尔强度；

(3)为了便于控制噪声效果，定义剔除阈值；

  Properties{//毛发噪声纹理_FurTex("Fur Texture", 2D) = "white" {}//毛发根部颜色[HDR]_RootColor("RootColor",Color)=(0,0,0,1)//毛发末端颜色[HDR]_FurColor("FurColor",Color)=(1,1,1,1)//凹凸纹理_BumpTex("Normal Map", 2D) = "bump" {}//凹凸强度_BumpIntensity("Bump Intensity",Range(0,2))=1//毛发长度_FurLength("Fur Length", Float) = 0.2//壳层总数_ShellCount("Shell Count", Float) = 16//边缘光颜色[HDR]_FresnelColor("Fresnel Color", Color) = (1,1,1,1)//菲涅尔强度_FresnelPower("Fresnel Power", Float) = 5//噪声剔除阈值_FurAlphaPow("Fur AlphaPow", Range(0,6)) = 1}

(2)顶点沿法线偏移

在顶点着色器中对顶点进行法线方向的偏移

 v2f vert(appdata v)
{v2f o;xxxxxxfloat shellIndex = _ShellIndex;float shellFrac = shellIndex / _ShellCount;float3 worldNormal = TransformObjectToWorldNormal(v.normal);float3 worldPos = TransformObjectToWorld(v.vertex.xyz);worldPos += worldNormal * (_FurLength * shellFrac);xxxxxxreturn o;
}

(3)噪声图透明度递减

 half4 frag(v2f i) : SV_Target{xxxxxxfloat mask = SAMPLE_TEXTURE2D(_FurTex, sampler_FurTex, i.uv).r;float alpha= saturate(mask - pow(shellFrac,_FurAlphaPow));xxxxxxxxxcol.a = alpha;xxxreturn col;}

(4)控制脚本传入壳层序号

在 Shader 中 没有直接的方法 获取实例编号（比如第几次调用的实例），比如SV_InstanceID在 Unity 的标准 Shader HLSL 里不暴露。UNITY_GET_INSTANCE_ID

UNITY_GET_INSTANCE_ID() 通常不生效，或者需要使用特殊渲染管线（如 HDRP + DOTS）。

所以，如果你不传 ShellIndex，Shader 就 不知道当前是第几层 Shel

(4)完整代码

C#控制脚本

[RequireComponent((typeof(MeshRenderer)))]
[ExecuteAlways]
public class ShellFurController_NonGpuInstancing : MonoBehaviour
{Mesh mesh;Material material;public int shellCount = 16;private Matrix4x4[] matrices;private MaterialPropertyBlock[] props;void Start(){//不调用 .material，这会创建一个新实例，浪费内存material = GetComponent<MeshRenderer>().sharedMaterial;mesh = GetComponent<MeshFilter>().sharedMesh;matrices = new Matrix4x4[shellCount];props = new MaterialPropertyBlock[shellCount];for (int i = 0; i < shellCount; i++){matrices[i] = transform.localToWorldMatrix;Debug.Log(matrices[i]);props[i] = new MaterialPropertyBlock();props[i].SetFloat("_ShellIndex", i);}}void Update(){//同步更新壳层世界位置for (int i = 0; i < shellCount; i++){matrices[i] = transform.localToWorldMatrix;Debug.Log(matrices[i]);props[i].SetFloat("_ShellIndex", i);}//使用DrawMesh API渲染多壳层for (int i = 0; i < shellCount; i++){Graphics.DrawMesh(mesh,matrices[i],material,           0,null,0,props[i],           UnityEngine.Rendering.ShadowCastingMode.Off,false);}}
}

UnlitShader

Shader "Unlit/Base_Shell_Fur_NonGpuIns"
{Properties{//毛发噪声纹理_FurTex("Fur Texture", 2D) = "white" {}//毛发根部颜色[HDR]_RootColor("RootColor",Color)=(0,0,0,1)//毛发末端颜色[HDR]_FurColor("FurColor",Color)=(1,1,1,1)//凹凸纹理_BumpTex("Normal Map", 2D) = "bump" {}//凹凸强度_BumpIntensity("Bump Intensity",Range(0,2))=1//毛发长度_FurLength("Fur Length", Float) = 0.2//壳层总数_ShellCount("Shell Count", Float) = 16//外发光颜色[HDR]_FresnelColor("Fresnel Color", Color) = (1,1,1,1)//菲涅尔强度_FresnelPower("Fresnel Power", Float) = 5//噪声剔除阈值_FurAlphaPow("Fur AlphaPow", Range(0,6)) = 1}SubShader{Tags { "Queue"="Transparent" "RenderType"="Transparent" }LOD 200ZWrite OffCull BackBlend SrcAlpha OneMinusSrcAlphaPass{Name "FurPass"Tags { "LightMode" = "UniversalForward" }HLSLPROGRAM#pragma vertex vert#pragma fragment frag#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"TEXTURE2D(_FurTex); SAMPLER(sampler_FurTex);float4 _FurTex_ST;TEXTURE2D(_BumpTex); SAMPLER(sampler_BumpTex);float _FurLength;float _ShellCount;float4 _FresnelColor;float _FresnelPower;float _FurAlphaPow;float4 _RootColor;float4 _FurColor;float _ShellIndex;//壳层序号，由C#控制脚本传入struct appdata{float4 vertex : POSITION;float3 normal : NORMAL;float2 uv : TEXCOORD0;};struct v2f{float4 pos : SV_POSITION;float2 uv : TEXCOORD0;float3 viewDir : TEXCOORD1;float3 worldNormal : TEXCOORD2;float shellIndex : TEXCOORD3;};v2f vert(appdata v){float shellIndex = _ShellIndex;float shellFrac = shellIndex / _ShellCount;v2f o;float3 worldNormal = TransformObjectToWorldNormal(v.normal);float3 worldPos = TransformObjectToWorld(v.vertex.xyz);worldPos += worldNormal * (_FurLength * shellFrac);o.pos = TransformWorldToHClip(worldPos);o.uv = TRANSFORM_TEX(v.uv, _FurTex);o.viewDir = normalize(_WorldSpaceCameraPos - worldPos);o.worldNormal = worldNormal;o.shellIndex = shellIndex;return o;}half4 frag(v2f i) : SV_Target{half4 col = SAMPLE_TEXTURE2D(_FurTex, sampler_FurTex, i.uv);float shellFrac = i.shellIndex / _ShellCount;float mask = SAMPLE_TEXTURE2D(_FurTex, sampler_FurTex, i.uv).r;float alpha= saturate(mask - pow(shellFrac,_FurAlphaPow));float3 bump = UnpackNormal(SAMPLE_TEXTURE2D(_BumpTex, sampler_BumpTex, i.uv));float3 normalWS = normalize(i.worldNormal + bump * 0.5);//边缘光float fresnel = pow(1.0 - saturate(dot(i.viewDir, normalWS)), _FresnelPower);//AOcol*=lerp(_RootColor,_FurColor,shellFrac);col.a = alpha;col.rgb += _FresnelColor.rgb * fresnel * alpha;return col;}ENDHLSL}}
}

(5)效果展示

(6)性能压力！！

当将控制脚本中的ShellCount设置到比较大的数值，我这里发现100层就比较卡了，试想如果这是真实的游戏场景，这性能压力简直是简直了，所以我决定采用GPUInstancing来优化我的项目。

运行前

运行后（场景内漫游时帧率急剧下降）

2.单通道(GPUInstancing)+DrawMeshInstansed实现优良性能

这里我采用Shader内StructruedBuffer搭配C#控制脚本内ComputeBuffer方案实现。

关于GPUInstancing的内容可以移步我的另一篇博客：Unity性能优化-渲染模块(1)-CPU侧(2)-DrawCall优化(2)GPUInstancing-CSDN博客

回顾绘制API的使用可以移步我的另一篇博客：

[学习记录]Unity中的绘制API-CSDN博客

(1)技术要点

1.合并 Draw Call：将所有实例的绘制合并成一个 Draw Call。

2.CPU 准备实例数据： 你需要在 CPU 上准备一个所有实例（壳层）的变换矩阵数组，使用ComputeBuffer作为一个所有实例的额外数据数组（例如，包含每个壳层索引的float数组）。通过material.SetBuffer传递给 Shader。

3.Shader 获取实例 ID： Shader 中会启用实例化，并通过内置的SV_InsatnceID获取当前正在处理的实例（壳层）的 ID。

(2)完整代码

C#控制脚本

using UnityEngine;[RequireComponent((typeof(MeshRenderer)))]
[ExecuteAlways]
public class ShellFurController_DrawInstanced : MonoBehaviour
{Mesh mesh; Material material;[Header("壳层数")]public int shellCount = 16;private Matrix4x4[] matrices;//使用DrawInstanced()，为了正确合批，使用统一的MPB，一次绘制所有实例private MaterialPropertyBlock props;private ComputeBuffer shellIndexBuffer;float[] shellIndices;void Start(){material = GetComponent<MeshRenderer>().sharedMaterial;mesh = GetComponent<MeshFilter>().sharedMesh;if (!material.enableInstancing){Debug.LogWarning("Fur material must enable GPU Instancing");}// 所有实例使用同一个 props，用数组传 ShellIndexmatrices = new Matrix4x4[shellCount];props = new MaterialPropertyBlock();shellIndices = new float[shellCount];for (int i = 0; i < shellCount; i++){matrices[i] = transform.localToWorldMatrix;shellIndices[i] = i;}shellIndexBuffer = new ComputeBuffer(shellCount, sizeof(float));shellIndexBuffer.SetData(shellIndices);material.SetBuffer("_ShellIndexBuffer", shellIndexBuffer);}void Update(){// 实例位置更新for (int i = 0; i < shellCount; i++){matrices[i] = transform.localToWorldMatrix;}// 使用真正的 GPU Instancing 调用Graphics.DrawMeshInstanced(mesh,0,material,matrices,shellCount,props,UnityEngine.Rendering.ShadowCastingMode.Off,false);}
}

UnlitShader

Shader "Unlit/Base_Shell_Fur_GpuIns"
{Properties{//毛发噪声纹理_FurTex("Fur Texture", 2D) = "white" {}//毛发根部颜色[HDR]_RootColor("RootColor",Color)=(0,0,0,1)//毛发末端颜色[HDR]_FurColor("FurColor",Color)=(1,1,1,1)//凹凸纹理_BumpTex("Normal Map", 2D) = "bump" {}//凹凸强度_BumpIntensity("Bump Intensity",Range(0,2))=1//毛发长度_FurLength("Fur Length", Float) = 0.2//壳层总数_ShellCount("Shell Count", Float) = 16//外发光颜色[HDR]_FresnelColor("Fresnel Color", Color) = (1,1,1,1)//菲涅尔强度_FresnelPower("Fresnel Power", Float) = 5//噪声剔除阈值_FurAlphaPow("Fur AlphaPow", Range(0,6)) = 1}SubShader{Tags { "Queue"="Transparent" "RenderType"="Transparent" }LOD 200ZWrite OffCull BackBlend SrcAlpha OneMinusSrcAlphaPass{Name "FurPass"Tags { "LightMode" = "UniversalForward" }HLSLPROGRAM#pragma vertex vert#pragma fragment frag#pragma multi_compile_instancing#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"TEXTURE2D(_FurTex); SAMPLER(sampler_FurTex);float4 _FurTex_ST;TEXTURE2D(_BumpTex); SAMPLER(sampler_BumpTex);float4 _BumpTex_ST;float _FurLength;float _ShellCount;float _WindStrength;float4 _FresnelColor;float _FresnelPower;float _FurAlphaPow;float4 _RootColor;float4 _FurColor;StructuredBuffer<float> _ShellIndexBuffer;struct appdata{float4 vertex : POSITION;float3 normal : NORMAL;float2 uv : TEXCOORD0;uint id: SV_InstanceID;};struct v2f{float4 pos : SV_POSITION;float2 uv : TEXCOORD0;float3 viewDir : TEXCOORD1;float3 worldNormal : TEXCOORD2;float shellIndex : TEXCOORD3;};v2f vert(appdata v){float shellIndex = _ShellIndexBuffer[v.id];float shellFrac = shellIndex / _ShellCount;v2f o;float3 worldNormal = TransformObjectToWorldNormal(v.normal);float3 worldPos = TransformObjectToWorld(v.vertex.xyz);float windOffset = sin(worldPos.x * 5 + _Time.y * 2 + shellIndex) * _WindStrength;worldPos += worldNormal * (_FurLength * shellFrac + windOffset);o.pos = TransformWorldToHClip(worldPos);o.uv = TRANSFORM_TEX(v.uv, _FurTex);o.viewDir = normalize(_WorldSpaceCameraPos - worldPos);o.worldNormal = worldNormal;o.shellIndex = shellIndex;return o;}half4 frag(v2f i) : SV_Target{half4 col = SAMPLE_TEXTURE2D(_FurTex, sampler_FurTex, i.uv);float shellFrac = i.shellIndex / _ShellCount;float mask = SAMPLE_TEXTURE2D(_FurTex, sampler_FurTex, i.uv).r;float alpha= saturate(mask - pow(shellFrac,_FurAlphaPow));float3 bump = UnpackNormal(SAMPLE_TEXTURE2D(_BumpTex, sampler_BumpTex, i.uv));float3 normalWS = normalize(i.worldNormal + bump * 0.5);float fresnel = pow(1.0 - saturate(dot(i.viewDir, normalWS)), _FresnelPower);//AOcol*=lerp(_RootColor,_FurColor,shellFrac);col.a = alpha;col.rgb += _FresnelColor.rgb * fresnel * alpha;return col;}ENDHLSL}}
}

(3)效果展示

渲染100层前后对比：

savebybatching：0->99

setPass Call : 24->25

这说明我们的GPUInstancng应用成功了。

3.单通道(GPUInstancing)+DrawMeshInstancedIndirect()实现极致性能

(1)技术要点

1.区别于DrawMeshInstanced

DrawMeshInstanced需要在 CPU 端传递一个固定数量的矩阵数组（最大 1023 个实例，超了会加批次），由 CPU 统一调度绘制。

DrawMeshInstancedIndirect是由 GPU 端驱动实例数量，可以动态控制实例数，且不受 1023 个实例的限制，效率更高，尤其适合实例数量变化或复杂实例计算场景。

(2)完整代码

C#控制脚本

using UnityEngine;
using UnityEngine.Rendering;
[ExecuteAlways]
public class ShellFurController_DrawInstancedIndirect : MonoBehaviour
{[Header("壳层数（动态可调）")] public int shellCount = 32;private Mesh mesh;private Material material;private ComputeBuffer argsBuffer;private ComputeBuffer shellIndexBuffer;private int lastShellCount = -1;private Camera mainCam;void Start(){mesh = GetComponent<MeshFilter>().sharedMesh;material = GetComponent<MeshRenderer>().sharedMaterial;mainCam = Camera.main;InitBuffers(); // 初次初始化}void Update(){/*Camera cam = Camera.current;if (!Application.isPlaying && UnityEditor.SceneView.currentDrawingSceneView != null)cam = UnityEditor.SceneView.currentDrawingSceneView.camera;*/if (shellCount != lastShellCount || argsBuffer == null || shellIndexBuffer == null){InitBuffers();lastShellCount = shellCount;}Graphics.DrawMeshInstancedIndirect(mesh,0,material,new Bounds(transform.position, Vector3.one * 100f),argsBuffer,0,null,ShadowCastingMode.On,true,gameObject.layer,mainCam,//这里绑的是Game窗口里的主相机，只会在Game窗口中渲染，场景视图中会不渲染，可以替换成上方的Scene窗口里的camLightProbeUsage.Off);}void InitBuffers(){// 清理旧 bufferargsBuffer?.Release();shellIndexBuffer?.Release();// 初始化 mesh/materialmesh ??= GetComponent<MeshFilter>().sharedMesh; material ??= GetComponent<MeshRenderer>().sharedMaterial;// 创建 DrawMeshInstancedIndirect 参数 bufferuint[] args = new uint[5] {(uint)mesh.GetIndexCount(0),(uint)shellCount,(uint)mesh.GetIndexStart(0),(uint)mesh.GetBaseVertex(0),0};argsBuffer = new ComputeBuffer(1, args.Length * sizeof(uint), ComputeBufferType.IndirectArguments);argsBuffer.SetData(args);// 创建 shell index buffer，传给 Shaderfloat[] shellIndices = new float[shellCount];for (int i = 0; i < shellCount; i++)shellIndices[i] = i;shellIndexBuffer = new ComputeBuffer(shellCount, sizeof(float));shellIndexBuffer.SetData(shellIndices);// 设置材质参数material.SetBuffer("_ShellIndexBuffer", shellIndexBuffer);material.SetInt("_ShellCount", shellCount);}void OnDisable(){argsBuffer?.Release();shellIndexBuffer?.Release();argsBuffer = null;shellIndexBuffer = null;}#if UNITY_EDITORvoid OnValidate(){lastShellCount = -1; // 强制重建 buffer}
#endif
}

UnlitShader和上面使用DrawMeshInstanced绘制的保持一致

Shader "Unlit/Base_Shell_Fur_GpuIns"
{Properties{//毛发噪声纹理_FurTex("Fur Texture", 2D) = "white" {}//毛发根部颜色[HDR]_RootColor("RootColor",Color)=(0,0,0,1)//毛发末端颜色[HDR]_FurColor("FurColor",Color)=(1,1,1,1)//凹凸纹理_BumpTex("Normal Map", 2D) = "bump" {}//凹凸强度_BumpIntensity("Bump Intensity",Range(0,2))=1//毛发长度_FurLength("Fur Length", Float) = 0.2//壳层总数_ShellCount("Shell Count", Float) = 16//外发光颜色[HDR]_FresnelColor("Fresnel Color", Color) = (1,1,1,1)//菲涅尔强度_FresnelPower("Fresnel Power", Float) = 5//噪声剔除阈值_FurAlphaPow("Fur AlphaPow", Range(0,6)) = 1}SubShader{Tags { "Queue"="Transparent" "RenderType"="Transparent" }LOD 200ZWrite OffCull BackBlend SrcAlpha OneMinusSrcAlphaPass{Name "FurPass"Tags { "LightMode" = "UniversalForward" }HLSLPROGRAM#pragma vertex vert#pragma fragment frag#pragma multi_compile_instancing#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"TEXTURE2D(_FurTex); SAMPLER(sampler_FurTex);float4 _FurTex_ST;TEXTURE2D(_BumpTex); SAMPLER(sampler_BumpTex);float4 _BumpTex_ST;float _FurLength;float _ShellCount;float _WindStrength;float4 _FresnelColor;float _FresnelPower;float _FurAlphaPow;float4 _RootColor;float4 _FurColor;StructuredBuffer<float> _ShellIndexBuffer;struct appdata{float4 vertex : POSITION;float3 normal : NORMAL;float2 uv : TEXCOORD0;uint id: SV_InstanceID;};struct v2f{float4 pos : SV_POSITION;float2 uv : TEXCOORD0;float3 viewDir : TEXCOORD1;float3 worldNormal : TEXCOORD2;float shellIndex : TEXCOORD3;};v2f vert(appdata v){float shellIndex = _ShellIndexBuffer[v.id];float shellFrac = shellIndex / _ShellCount;v2f o;float3 worldNormal = TransformObjectToWorldNormal(v.normal);float3 worldPos = TransformObjectToWorld(v.vertex.xyz);float windOffset = sin(worldPos.x * 5 + _Time.y * 2 + shellIndex) * _WindStrength;worldPos += worldNormal * (_FurLength * shellFrac + windOffset);o.pos = TransformWorldToHClip(worldPos);o.uv = TRANSFORM_TEX(v.uv, _FurTex);o.viewDir = normalize(_WorldSpaceCameraPos - worldPos);o.worldNormal = worldNormal;o.shellIndex = shellIndex;return o;}half4 frag(v2f i) : SV_Target{half4 col = SAMPLE_TEXTURE2D(_FurTex, sampler_FurTex, i.uv);float shellFrac = i.shellIndex / _ShellCount;float mask = SAMPLE_TEXTURE2D(_FurTex, sampler_FurTex, i.uv).r;float alpha= saturate(mask - pow(shellFrac,_FurAlphaPow));float3 bump = UnpackNormal(SAMPLE_TEXTURE2D(_BumpTex, sampler_BumpTex, i.uv));float3 normalWS = normalize(i.worldNormal + bump * 0.5);float fresnel = pow(1.0 - saturate(dot(i.viewDir, normalWS)), _FresnelPower);//AOcol*=lerp(_RootColor,_FurColor,shellFrac);col.a = alpha;col.rgb += _FresnelColor.rgb * fresnel * alpha;return col;}ENDHLSL}}
}