用 unity shaderlab 编写一个 lambert shader

以下是一个简单的Lambert着色器，它使用Unity的Standard Surface Shader来定义其表面属性：

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

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

        CGPROGRAM
        #pragma surface surf Lambert

        //定义表面属性
        struct Input {
            float2 uv_MainTex;
            float3 worldPos;
        };

        //定义表面函数
        void surf (Input IN, inout SurfaceOutputStandard o) {
            //设置基本属性
            o.Albedo = _Color.rgb;
            o.Metallic = 0.0;
            o.Smoothness = 0.5;
            o.Normal = float3(0,0,1);

            //计算光照
            float3 lightDir = normalize(_WorldSpaceLightPos0.xyz - IN.worldPos);
            float diffuse = max(0, dot(IN.worldNormal, lightDir));
            o.Emission = _Color.rgb * diffuse;
        }

        ENDCG
    }
    FallBack "Diffuse"
}