Shader "Custom/Diffuse HalfLambert"
{
    Properties
    {
        _Diffuse ("Diffuse", Color) = (1,1,1,1)
    }

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

        Pass
        {
            Tags { "LightMode"="ForwardBase" }        // 只有设置了正确的LightMode，才能访问一些Unity提供的内置变量，如：_LightColor0
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

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

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

            struct v2f
            {
                float4 vertex : SV_POSITION;
                fixed4 color : COLOR;
            };

            float4 _Diffuse;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);

                float3 lightDir = ObjSpaceLightDir(v.vertex);
                lightDir = normalize(lightDir);
                float halfLambert = dot(lightDir, v.normal) * 0.5 + 0.5;        // 将dot的结果从[-1,1]映射到[0,1]范围
                float4 diffuseColor = _Diffuse * _LightColor0 * halfLambert;

                o.color = UNITY_LIGHTMODEL_AMBIENT + diffuseColor;
                return o;
            }
            
            fixed4 frag (v2f i) : SV_Target
            {
                return i.color;
            }
            ENDCG
        }
    }

    Fallback "Diffuse"
}