1.最简形式，只根据顶点的法线和光照的方向做点积来计算

// Upgrade NOTE: replaced '_World2Object' with 'unity_WorldToObject'

Shader "Custom/PhongVert2"
{
    Properties
    {
        _Diffuse ("Diffuse", COLOR) = (1,1,1,1)
    }
    SubShader
    {
        Tags { "RenderType" = "Opaque" 
                "LightMode" = "ForwardBase"
        }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"
            #include "Lighting.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float3 normal : NORMAL;
            };

            struct v2f
            {
                fixed3 color : COLOR;
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            fixed4 _Diffuse;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                fixed3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
                fixed3 worldNormal = normalize( mul( v.normal,(fixed3x3)unity_WorldToObject ) );
                //_WorldSpaceLightPos0 是光的方向向量
                fixed3 worldLight = normalize(_WorldSpaceLightPos0.xyz);
                fixed3 diffuse = _LightColor0.rgb * _Diffuse.rgb * saturate(dot(worldNormal,worldLight));
                o.color = ambient + diffuse;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                return fixed4(i.color,1);
            }
            ENDCG
        }
    }
}

效果: