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| Shader "Hidden/AtmosphericScattering"
{
Properties
{
_EarthRadius("EarthRadius",float)=1600
_AtmosphereHeight("AtmosphereHeight",float)=1000
_H("H0(大气平均密度所在的高度)",float)=2000
//_betaMie("β(λ)Mie",float)=0.9
_betaRL("β(λ)RL",float)=0.9
_SunColor("SunColor",Color)=(1,1,1,1)
}
SubShader
{
Tags { "LightMode" = "UniversalForward"}
LOD 100
Pass
{
HLSLPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"
struct appdata
{
float4 vertex : POSITION;
float2 uv : TEXCOORD0;
};
struct v2f
{
float2 uv : TEXCOORD0;
float4 vertex : SV_POSITION;
//float4 rayVS:TEXCOORD1;
};
CBUFFER_START(UnityPerMaterial)
float _EarthRadius;
float _AtmosphereHeight;
float _H;
//float _betaMie;
float _betaRL;
half4 _SunColor;
CBUFFER_END
TEXTURE2D(_CameraDepthTexture); SAMPLER(sampler_CameraDepthTexture);
// float getLen2(float3 pos,float3 dir,float R,float3 centerPos)
// {
// float3 ACenter=centerPos-pos;
// float lenACenter=length(ACenter);
// float cosTheta=dot(normalize(ACenter),dir);
// //
// float lenAC=lenACenter*cosTheta;
// float lenO2C= sqrt(lenACenter*lenACenter-lenAC*lenAC);
// float lenA2C=sqrt(R*R-lenO2C*lenO2C);
// float lenAA2=lenA2C-lenAC;
// float lenBC=lenA2C;
// float AB=cosTheta>0?lenBC+lenAC:lenBC-lenAC;
// return AB;
// }
float getLen(float3 pos, float3 dir, float R,float3 centerPos)
{
float3 PO = centerPos - pos;
float lPO = length(PO);
float B = 2.0*dot(PO, dir);
float C = B*B - 4*(lPO*lPO-R*R);
float det = sqrt( max(0, C) );
//elsed: .5*(B+det)
float d = 0.5*(B-det);
float3 intersect = pos+d*dir;
return distance(intersect,pos);
}
v2f vert (appdata v)
{
v2f o;
o.vertex = TransformObjectToHClip(v.vertex);
o.uv = v.uv;
#if UNITY_UV_STARTS_TOP
o.uv.y=1-o.uv.y;
#endif
return o;
}
half4 frag (v2f i) : SV_Target
{
float depth = SAMPLE_TEXTURE2D(_CameraDepthTexture,sampler_CameraDepthTexture,i.uv);
float3 posWS=ComputeWorldSpacePosition( i.uv,depth, UNITY_MATRIX_I_VP);
//return half4(posWS,1);
//
float3 viewDir=_WorldSpaceCameraPos-posWS;
float viewLen=length(viewDir);
viewDir=-normalize(viewDir);
Light light=GetMainLight();
float3 lightDir=light.direction;
float LdotV=dot(lightDir,-viewDir);
float3 centerWS=float3(0,-_EarthRadius,0); //世界空间原点（0,0,0）作为表面起始位置，地心则在正下方R处
float maxStepCount=20;
float3 PPos=_WorldSpaceCameraPos;
//float PALen=getLen(PPos,viewDir,_AtmosphereHeight+_EarthRadius,centerWS);
float PALen=min(getLen(PPos,viewDir,_AtmosphereHeight+_EarthRadius,centerWS),LinearEyeDepth(depth,_ZBufferParams));
float3 stepRay=(viewDir*PALen)/maxStepCount;
float stepRaySize=length(stepRay);
float opticalDepthPA=0;
float T=0;
for(float k=0.5;k<maxStepCount;++k)
{
PPos=_WorldSpaceCameraPos+stepRay*k; //P步进
//==========DCP
float CPLen=getLen(PPos,lightDir,_AtmosphereHeight+_EarthRadius,centerWS);
//float3 CPos=PPos+lightDir*CPLen;
float3 stepCP=(lightDir*CPLen)/maxStepCount;
float stepCPSize=length(stepCP);
float opticalDepthCP=0;
for(float j=0.5;j<maxStepCount;++j)
{
float3 pos=PPos+stepCP*j;
float h=abs(length(pos-centerWS)-_EarthRadius);
opticalDepthCP+=exp(-(h/_H) )* stepCPSize ;
}
//============DCPEnd
//PA路径上
float PALen=distance(_WorldSpaceCameraPos,PPos);
float3 stepPA=PALen*viewDir/maxStepCount;
float stepPASize=length(stepPA);
float3 pSamplePos=PPos;
for(float g=0;g<maxStepCount;++g) //P
{
opticalDepthPA+=exp(-abs(length(PPos-centerWS)-_EarthRadius)/_H)*stepPASize;
pSamplePos+=stepPA;
}
T+= exp(-_betaRL*(opticalDepthCP+opticalDepthPA))*exp(-abs(length(PPos-centerWS)-_EarthRadius)/_H)*stepRaySize; //T项
}
//相位函数
float phase=(3.0 / (16.0 * 3.1415926)) * (1.0+ (LdotV * LdotV));
float3 I_A=_SunColor.rgb*T*_betaRL*phase;
// return T;
return half4(I_A.rgb,1);
}
ENDHLSL
}
}
}
|
