Shader "Unlit/PlanarShadow"
{

    SubShader
    {
        HLSLINCLUDE
        
        #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
        #include "Packages/com.unity.render-pipelines.core/ShaderLibrary/Common.hlsl"

	    #ifdef LOW_SOFT_QUALITY
		    #define OPERATOR_SIZE 10
	    #elif defined(MEDIUM_SOFT_QUALITY)
		    #define OPERATOR_SIZE 16
	    #else
		    #define OPERATOR_SIZE 32
	    #endif

	    struct Varyings
	    {
		    float4 vertex : SV_POSITION;
		    float2 uv         : TEXCOORD0;
	    };

	    TEXTURE2D(_SourceTex);
	    SAMPLER(sampler_SourceTex);

	    TEXTURE2D(_DistanceTex);
	    SAMPLER(sampler_DistanceTex);

	    SAMPLER(sampler_LinearClamp);

	    float4 _PossionOperator[32];
	    float4 _EdgeMapTexelSize;
	    float4 _SourceTex_TexelSize;
	    float2 _ShadowScreenHDir;
	    float2 _ShadowScreenVDir;
	    float _MinSoft;
	    float _SoftScaleByDistance;
    
        Varyings FullScreenVert(uint vertexID: SV_VertexID)
        {
            Varyings o;
            o.vertex = GetFullScreenTriangleVertexPosition(vertexID);
            o.uv = GetFullScreenTriangleTexCoord(vertexID);
            return o;
        }

	    half4 buildSoftEdgeVFrag(Varyings input) : SV_Target
	    {
		    half2 uv = input.uv;
		    half2 uvStep = _EdgeMapTexelSize.xy * _ShadowScreenVDir * 0.6f;
		    UNITY_UNROLL
		    for(int i = 0;i<4;i++)
		    {
			    half dis = SAMPLE_TEXTURE2D(_SourceTex, sampler_SourceTex, uv - i * uvStep).r;
			    if(dis > 0)
				    return dis;
		    }

		    return 0;
	    }

	    half4 buildSoftEdgeHFrag(Varyings input) : SV_Target
	    {
		    half2 uv = input.uv;
		    half2 uvStep = _SourceTex_TexelSize.xy * _ShadowScreenHDir* 0.6f;
		    UNITY_UNROLL
		    for(int i = 0; i < 6; i++)
		    {
			    half dis = SAMPLE_TEXTURE2D(_SourceTex, sampler_SourceTex, uv - i * uvStep).r;
			    half dis2 = SAMPLE_TEXTURE2D(_SourceTex, sampler_SourceTex, uv + i * uvStep).r;
			    if(dis > 0)
				    return dis;
			    if(dis2 > 0)
				    return dis2;
		    }

		    return 0;
	    }


	    half4 CircleVisiualFrag(Varyings input) : SV_Target
	    {
		    half2 uv = input.uv;
		    half blurSize = SAMPLE_TEXTURE2D(_DistanceTex, sampler_DistanceTex, uv).r;
		    half2 uvStep = _SourceTex_TexelSize.xy * (_MinSoft + (1 - _MinSoft) * blurSize) * _SoftScaleByDistance;
		    half col = 0;
		
		    if(blurSize == 0)
			    return SAMPLE_TEXTURE2D(_SourceTex, sampler_LinearClamp, uv).g;
		    UNITY_UNROLL
		    for(int i = 0; i < OPERATOR_SIZE;i++)
		    {
			    col += SAMPLE_TEXTURE2D(_SourceTex, sampler_LinearClamp, uv + uvStep * _PossionOperator[i].xy).g * _PossionOperator[i].z;
		    }
		    return half4(col.rrr,1);
	    }

        ENDHLSL
        
        Pass
        {
            Name "BlurV"    
                  
            HLSLPROGRAM
            #pragma vertex FullScreenVert
            #pragma fragment buildSoftEdgeVFrag
            ENDHLSL
        }
         
        Pass
        {
            Name "BlurH"    
                 
            HLSLPROGRAM
            #pragma vertex FullScreenVert
            #pragma fragment buildSoftEdgeHFrag
            ENDHLSL
        }

        Pass
        {
            Name "CircleVisiual"    
  
            HLSLPROGRAM
            #pragma multi_compile _ LOW_SOFT_QUALITY MEDIUM_SOFT_QUALITY
            #pragma vertex FullScreenVert
            #pragma fragment CircleVisiualFrag
            ENDHLSL
        }

        Pass
        {
            Tags { "LightMode" = "PlanarShadow" } 
            
            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_instancing
       #pragma enable_d3d11_debug_symbols
            #pragma shader_feature_local TRANSPARENT_SHADOW_CASTER 
      
            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
            #include "Packages/com.unity.render-pipelines.core/ShaderLibrary/Common.hlsl"
      
            float4 _PlanarShadowCastPlane;
            float _PlanarShadowMaxSoftDistance;
            half4 _PlanarShadowColor;
            
            TEXTURE2D(_PlanarShadowMap);
            SAMPLER(sampler_PlanarShadowMap);
            
            void CastVertexToPlane(float3 oriPositionWS, float3 lightDirection, out float3 positionWS, out float shadowSoftScale, float objtY)
            {
                float3 planeNor = _PlanarShadowCastPlane.xyz;
            	float w = _PlanarShadowCastPlane.w + objtY;
            	// https://zhuanlan.zhihu.com/p/42781261 
                float castDistance = (w - dot(oriPositionWS.xyz, planeNor)) / dot(lightDirection, planeNor);
                positionWS = oriPositionWS.xyz + castDistance * lightDirection;
                shadowSoftScale = max(0, castDistance / _PlanarShadowMaxSoftDistance);
            }
            
            half3 GetPlanarScreenShadowAttenuation(float2 screenUV)
            {
            #ifdef PLANAR_SHADOW
                half attenutaion = SAMPLE_TEXTURE2D(_PlanarShadowMap, sampler_PlanarShadowMap, screenUV).r;
                return lerp(1, _PlanarShadowColor, attenutaion);
            #else
                return 1;
            #endif
            }

            struct attribute
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD;
            };
 
            struct v2f
            {
                float4 vertex : SV_POSITION;
                float2 uv : TEXCOORD0;
                float softValue : TEXCOORD1;
            };

            sampler2D _MainTexture;

            v2f vert (attribute v)
            {
                v2f o;
                float4 worldPos = mul(UNITY_MATRIX_M, v.vertex); 
                float3 lightDir = -_MainLightPosition.xyz;
				float y = UNITY_MATRIX_M[1][3];
                float3 castPosWS;
                float softValue;
                CastVertexToPlane(worldPos.xyz, lightDir, castPosWS, softValue, y);
                o.softValue = softValue;
                o.vertex = mul(UNITY_MATRIX_VP, float4(castPosWS, 1));
                o.uv = v.uv;
                return o;
            }
       
            half4 frag (v2f i) : SV_Target
            {
            #ifdef TRANSPARENT_SHADOW_CASTER
                float4 col = tex2D(_MainTexture, i.uv);
            #else
                float4 col = 1;
            #endif
                return half4(i.softValue,col.a,0, 0);
            }
            ENDHLSL
        }
    }
}