[Unity]开启材质GPU Instancing，合批相同材质不同颜色的物体。

1. 在自定义shader里添加宏定义：

#pragma multi_compile_instancing

然后在材质的Inspector栏可以看到GPU Instancing选项，勾选即可。

2. 在自定义shader定义属性的代码下添加：

     UNITY_INSTANCING_BUFFER_START(Props)
         UNITY_DEFINE_INSTANCED_PROP(half4, _Color)
     UNITY_INSTANCING_BUFFER_END(Props)

2. 在自定义shader的输入输出结构体里添加代码：
 

UNITY_VERTEX_INPUT_INSTANCE_ID

3. 在自定义shader的输入输出函数内添加代码：

UNITY_SETUP_INSTANCE_ID(v);

UNITY_SETUP_INSTANCE_ID(i);

下面是Unity官方shader示例：

1. 表面着色器

Shader "Custom/InstancedColorSurfaceShader"
{
    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
        // Uses the physically based standard lighting model with shadows enabled for all light types.
        #pragma surface surf Standard fullforwardshadows
        // Use Shader model 3.0 target
        #pragma target 3.0
        sampler2D _MainTex;
        struct Input
        {
            float2 uv_MainTex;
        };
        half _Glossiness;
        half _Metallic;
        UNITY_INSTANCING_BUFFER_START(Props)
           UNITY_DEFINE_INSTANCED_PROP(fixed4, _Color)
        UNITY_INSTANCING_BUFFER_END(Props)
        void surf (Input IN, inout SurfaceOutputStandard o) {
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * UNITY_ACCESS_INSTANCED_PROP(Props, _Color);
            o.Albedo = c.rgb;
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = c.a;
        }
        ENDCG
    }
    FallBack "Diffuse"
}

2. 顶点片元着色器

Shader "Custom/SimplestInstancedShader"
{
    Properties
    {
        _Color ("Color", Color) = (1, 1, 1, 1)
    }

    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_instancing
            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct v2f
            {
                float4 vertex : SV_POSITION;
                UNITY_VERTEX_INPUT_INSTANCE_ID // use this to access instanced properties in the fragment shader.
            };

            UNITY_INSTANCING_BUFFER_START(Props)
                UNITY_DEFINE_INSTANCED_PROP(float4, _Color)
            UNITY_INSTANCING_BUFFER_END(Props)

            v2f vert(appdata v)
            {
                v2f o;

                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_TRANSFER_INSTANCE_ID(v, o);
                o.vertex = UnityObjectToClipPos(v.vertex);
                return o;
            }

            fixed4 frag(v2f i) : SV_Target
            {
                UNITY_SETUP_INSTANCE_ID(i);
                return UNITY_ACCESS_INSTANCED_PROP(Props, _Color);
            }
            ENDCG
        }
    }
}