gpu instancer crowd 使用自定义材质并且只修改单个物体的材质参数

gpu instancer 中由于所有物体只使用同一个材质和网格，不像普通渲染每一个物体都有单独的材质副本，所以大量物体渲染只需要使用一次draw call
，节省了很多性能。而修改单个物体材质的方式也跟普通渲染不一样，每个物体有自己的参数buff，着色器需要获取参数时只需要根据实例id在这个buff中获取参数。
gpu instancer crowd 中也要在着色器中修改才能自定义着色器，根据这个非常反人类的文档，自定义着色器那么重要的部分一部分写在crowd 说明中，一部分写在q&a中
urp中引入cginc文件和 #pragma

Pass {...HLSLPROGRAM...#pragma multi_compile_instancing#pragma instancing_options procedural:setupGPUI...#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"#include "Packages/com.unity.render-pipelines.core/ShaderLibrary/Color.hlsl"#include "Packages/com.unity.render-pipelines.core/ShaderLibrary/UnityInstancing.hlsl"#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/ShaderGraphFunctions.hlsl"#include "./../../../GPUInstancer/Shaders/Include/GPUInstancerInclude.cginc"#include "./../../../GPUInstancer-CrowdAnimations/Shaders/Include/GPUICrowdInclude.cginc"#pragma multi_compile _ GPUI_CA_BINDPOSEOFFSET#pragma shader_feature_vertex GPUI_CA_TEXTURE#pragma multi_compile_instancing#pragma instancing_options procedural:setupGPUI...ENDHLSL
}

在顶点着色器加入GPUI_CROWD_VERTEX

v2f vert(appdata_full v)
{v2f o;UNITY_SETUP_INSTANCE_ID(v);GPUI_CROWD_VERTEX(v);...return o;
}

但其实GPUI_CROWD_VERTEX会报错，非常弱智，根据一个隐秘的示例shader 使用gpuiCASkinning才是不会报错的，GPUI_CROWD_VERTEX就是gpuiCASkinning的封装

v2f vert(appdata_full v)
{v2f o;UNITY_SETUP_INSTANCE_ID(v);gpuiCASkinning(v.texcoord2, v.texcoord3, v.vertex.xyz, v.normal.xyz, v.tangent.xyz, v.vertex.xyz, v.normal.xyz, v.tangent.xyz);...return o;
}

自定义的appdata一定要有texcoord2 texcoord3

struct appdata_custom 
{float4 vertex : POSITION;float4 tangent : TANGENT;float3 normal : NORMAL;float4 texcoord2 : TEXCOORD2;float4 texcoord3 : TEXCOORD3;UNITY_VERTEX_INPUT_INSTANCE_ID
};

自定义的加入

#define GPUI_CUSTOM_INPUT 1 // needs to be declared so GPUI does not override your defines
#define GPUI_STRUCT_NAME appdata_custom // the name of your input struct
#define GPUI_BONE_INDEX texcoord2 // TEXCOORD2
#define GPUI_BONE_WEIGHT texcoord3 // TEXCOORD3
#define GPUI_VERTEX vertex // VERTEX
#define GPUI_NORMAL normal // NORMAL
#define GPUI_TANGENT tangent // TANGENT

至此，自定义shader就没有问题了
那如何只修改单个物体的材质参数
首先在shader中加入

	uniform StructuredBuffer<float4> gpuiFloat4Variation;float4 gpuiF4Var_float( float4 Float4_Out)
{#ifdef UNITY_PROCEDURAL_INSTANCING_ENABLEDFloat4_Out = gpuiFloat4Variation[gpui_InstanceID];#elseFloat4_Out = float4(1, 1, 1, 1);#endifreturn Float4_Out;
}

gpuiFloat4Variation是buff的名字 ，单个gpu instance使用时通过gpui_InstanceID在buff中获取属于它的数据

 void Start(){// Define the buffer to the Prefab Manager.if (prefabManager != null && prefabManager.isActiveAndEnabled){GPUInstancerAPI.DefinePrototypeVariationBuffer<Vector4>(prefabManager, prefab.prefabPrototype, bufferName);}}

来自demo里的ColorVariations脚本，首先注册这个buff，bufferName是gpuiFloat4Variation，一定要相同
生成物体后进行加入参数

 prefabInstance.AddVariation(bufferName, (Vector4)Random.ColorHSV());

修改物体材质颜色参数，goList为生成的物体的list

   Vector4 v = (Vector4)Random.ColorHSV();GPUInstancerAPI.UpdateVariation(prefabManager, goList[Random.Range(0, goList.Count)], bufferName, v);