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147 lines
5.0 KiB
147 lines
5.0 KiB
// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'
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// Upgrade NOTE: replaced '_Object2World' with 'unity_ObjectToWorld'
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Shader "Atmosphere/SkyFromSpace"
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{
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SubShader
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{
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Tags {"Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent"}
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//Tags { "RenderType"="Opaque" }
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Pass
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{
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Blend SrcAlpha OneMinusSrcAlpha
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ZWrite Off
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Cull Front
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//Blend One One
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CGPROGRAM
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#include "UnityCG.cginc"
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#pragma target 3.0
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#pragma vertex vert
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#pragma fragment frag
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uniform float3 v3Translate; // The objects world pos
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uniform float3 v3LightPos; // The direction vector to the light source
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uniform float3 v3InvWavelength; // 1 / pow(wavelength, 4) for the red, green, and blue channels
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uniform float fOuterRadius; // The outer (atmosphere) radius
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uniform float fOuterRadius2; // fOuterRadius^2
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uniform float fInnerRadius; // The inner (planetary) radius
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uniform float fInnerRadius2; // fInnerRadius^2
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uniform float fKrESun; // Kr * ESun
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uniform float fKmESun; // Km * ESun
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uniform float fKr4PI; // Kr * 4 * PI
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uniform float fKm4PI; // Km * 4 * PI
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uniform float fScale; // 1 / (fOuterRadius - fInnerRadius)
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uniform float fScaleDepth; // The scale depth (i.e. the altitude at which the atmosphere's average density is found)
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uniform float fScaleOverScaleDepth; // fScale / fScaleDepth
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uniform float fHdrExposure; // HDR exposure
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uniform float g; // The Mie phase asymmetry factor
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uniform float g2; // The Mie phase asymmetry factor squared
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struct v2f
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{
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float4 pos : SV_POSITION;
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float2 uv : TEXCOORD0;
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float3 t0 : TEXCOORD1;
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float3 c0 : COLOR0;
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float3 c1 : COLOR1;
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};
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float scale(float fCos)
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{
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float x = 1.0 - fCos;
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return 0.25 * exp(-0.00287 + x*(0.459 + x*(3.83 + x*(-6.80 + x*5.25))));
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}
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v2f vert(appdata_base v)
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{
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float3 v3CameraPos = _WorldSpaceCameraPos - v3Translate; // The camera's current position
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float fCameraHeight = length(v3CameraPos); // The camera's current height
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float fCameraHeight2 = fCameraHeight*fCameraHeight; // fCameraHeight^2
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// Get the ray from the camera to the vertex and its length (which is the far point of the ray passing through the atmosphere)
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float3 v3Pos = mul(unity_ObjectToWorld, v.vertex).xyz - v3Translate;
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float3 v3Ray = v3Pos - v3CameraPos;
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float fFar = length(v3Ray);
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v3Ray /= fFar;
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// Calculate the closest intersection of the ray with the outer atmosphere (which is the near point of the ray passing through the atmosphere)
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float B = 2.0 * dot(v3CameraPos, v3Ray);
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float C = fCameraHeight2 - fOuterRadius2;
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float fDet = max(0.0, B*B - 4.0 * C);
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float fNear = 0.5 * (-B - sqrt(fDet));
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// Calculate the ray's start and end positions in the atmosphere, then calculate its scattering offset
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float3 v3Start = v3CameraPos + v3Ray * fNear;
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fFar -= fNear;
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float fStartAngle = dot(v3Ray, v3Start) / fOuterRadius;
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float fStartDepth = exp(-1.0/fScaleDepth);
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float fStartOffset = fStartDepth*scale(fStartAngle);
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const float fSamples = 2.0;
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// Initialize the scattering loop variables
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float fSampleLength = fFar / fSamples;
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float fScaledLength = fSampleLength * fScale;
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float3 v3SampleRay = v3Ray * fSampleLength;
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float3 v3SamplePoint = v3Start + v3SampleRay * 0.5;
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// Now loop through the sample rays
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float3 v3FrontColor = float3(0.0, 0.0, 0.0);
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for(int i=0; i<int(fSamples); i++)
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{
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float fHeight = length(v3SamplePoint);
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float fDepth = exp(fScaleOverScaleDepth * (fInnerRadius - fHeight));
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float fLightAngle = dot(v3LightPos, v3SamplePoint) / fHeight;
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float fCameraAngle = dot(v3Ray, v3SamplePoint) / fHeight;
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float fScatter = (fStartOffset + fDepth*(scale(fLightAngle) - scale(fCameraAngle)));
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float3 v3Attenuate = exp(-fScatter * (v3InvWavelength * fKr4PI + fKm4PI));
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v3FrontColor += v3Attenuate * (fDepth * fScaledLength);
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v3SamplePoint += v3SampleRay;
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}
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v2f OUT;
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OUT.pos = UnityObjectToClipPos(v.vertex);
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OUT.uv = v.texcoord.xy;
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// Finally, scale the Mie and Rayleigh colors and set up the varying variables for the pixel shader
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OUT.c0 = v3FrontColor * (v3InvWavelength * fKrESun);
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OUT.c1 = v3FrontColor * fKmESun;
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OUT.t0 = v3CameraPos - v3Pos;
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return OUT;
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}
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// Calculates the Mie phase function
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float getMiePhase(float fCos, float fCos2, float g, float g2)
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{
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return 1.5 * ((1.0 - g2) / (2.0 + g2)) * (1.0 + fCos2) / pow(1.0 + g2 - 2.0*g*fCos, 1.5);
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}
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// Calculates the Rayleigh phase function
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float getRayleighPhase(float fCos2)
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{
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return 0.75 + 0.75*fCos2;
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}
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half4 frag(v2f IN) : COLOR
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{
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float fCos = dot(v3LightPos, IN.t0) / length(IN.t0);
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float fCos2 = fCos*fCos;
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float3 col = getRayleighPhase(fCos2) * IN.c0 + getMiePhase(fCos, fCos2, g, g2) * IN.c1;
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col = 1.0 - exp(col * -fHdrExposure);
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return float4(col,col.b);
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}
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ENDCG
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}
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}
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}
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