// 案例 23.9：接收接触阴影的简单光照 Shader。
// 阴影 = min(阴影贴图结果, 接触阴影结果)：远处的大阴影交给 Shadow Map，脚底的细节交给接触阴影。
Shader "Cookbook/Ch23/ContactShadowLit"
{
    Properties
    {
        [MainTexture] _BaseMap ("Base Map", 2D) = "white" {}
        [MainColor]   _BaseColor ("Base Color", Color) = (1, 1, 1, 1)
        [Toggle] _UseContact ("Use Contact Shadow", Float) = 1
        [Toggle] _ShowContact ("Debug: 只显示接触阴影", Float) = 0
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" "RenderPipeline"="UniversalPipeline" "Queue"="Geometry" }
        HLSLINCLUDE
        #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
        CBUFFER_START(UnityPerMaterial)
            float4 _BaseMap_ST;
            half4  _BaseColor;
            half   _UseContact;
            half   _ShowContact;
        CBUFFER_END
        ENDHLSL

        Pass
        {
            Name "ForwardLit"
            Tags { "LightMode"="UniversalForward" }
            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile _ _MAIN_LIGHT_SHADOWS _MAIN_LIGHT_SHADOWS_CASCADE _MAIN_LIGHT_SHADOWS_SCREEN
            #pragma multi_compile_fragment _ _SHADOWS_SOFT _SHADOWS_SOFT_LOW _SHADOWS_SOFT_MEDIUM _SHADOWS_SOFT_HIGH
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"

            TEXTURE2D(_BaseMap); SAMPLER(sampler_BaseMap);
            TEXTURE2D(_ContactShadowTexture);

            struct Attributes { float4 positionOS : POSITION; float3 normalOS : NORMAL; float2 uv : TEXCOORD0; };
            struct Varyings { float4 positionCS : SV_POSITION; float2 uv : TEXCOORD0; float3 positionWS : TEXCOORD1; half3 normalWS : TEXCOORD2; };

            Varyings vert(Attributes v)
            {
                Varyings o;
                VertexPositionInputs p = GetVertexPositionInputs(v.positionOS.xyz);
                o.positionCS = p.positionCS; o.positionWS = p.positionWS;
                o.normalWS = TransformObjectToWorldNormal(v.normalOS);
                o.uv = TRANSFORM_TEX(v.uv, _BaseMap);
                return o;
            }

            half4 frag(Varyings i) : SV_Target
            {
                half3 albedo = SAMPLE_TEXTURE2D(_BaseMap, sampler_BaseMap, i.uv).rgb * _BaseColor.rgb;
                half3 n = normalize(i.normalWS);
                Light l = GetMainLight(TransformWorldToShadowCoord(i.positionWS), i.positionWS, half4(1, 1, 1, 1));

                half contact = 1;
                if (_UseContact > 0.5)
                {
                    float2 screenUV = GetNormalizedScreenSpaceUV(i.positionCS);
                    contact = SAMPLE_TEXTURE2D(_ContactShadowTexture, sampler_LinearClamp, screenUV).r;
                }
                if (_ShowContact > 0.5) return half4(contact.xxx, 1);

                half shadow = min(l.shadowAttenuation, contact);
                half3 c = albedo * (l.color * saturate(dot(n, l.direction)) * shadow + SampleSH(n));
                return half4(c, 1);
            }
            ENDHLSL
        }
        Pass
        {
            Name "ShadowCaster"
            Tags { "LightMode"="ShadowCaster" }
            ZWrite On ZTest LEqual ColorMask 0
            HLSLPROGRAM
            #pragma vertex Ch23ShadowCasterVert
            #pragma fragment Ch23NullFrag
            #pragma multi_compile_vertex _ _CASTING_PUNCTUAL_LIGHT_SHADOW
            #include "Assets/Cookbook/Ch23/Ch23Common.hlsl"
            ENDHLSL
        }
        Pass
        {
            Name "DepthOnly"
            Tags { "LightMode"="DepthOnly" }
            ZWrite On ColorMask R
            HLSLPROGRAM
            #pragma vertex Ch23DepthOnlyVert
            #pragma fragment Ch23NullFrag
            #include "Assets/Cookbook/Ch23/Ch23Common.hlsl"
            ENDHLSL
        }
    }
}