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#include "AtmosphereShadersCommon.fxh"
cbuffer cbParticipatingMediaScatteringParams
{
AirScatteringAttribs g_MediaParams;
}
Texture2D<float2> g_tex2DOccludedNetDensityToAtmTop;
SamplerState g_tex2DOccludedNetDensityToAtmTop_sampler;
#include "LookUpTables.fxh"
#include "PrecomputeCommon.fxh"
#include "ScatteringIntegrals.fxh"
Texture3D<float3> g_tex3DPreviousSctrOrder;
SamplerState g_tex3DPreviousSctrOrder_sampler;
Texture2D<float3> g_tex2DSphereRandomSampling;
RWTexture3D</*format = rgba32f*/float3> g_rwtex3DSctrRadiance;
// This shader pre-computes the radiance of light scattered at a given point in given
// direction. It multiplies the previous order in-scattered light with the phase function
// for each type of particles and integrates the result over the whole set of directions,
// see eq. (7) in [Bruneton and Neyret 08].
[numthreads(THREAD_GROUP_SIZE, THREAD_GROUP_SIZE, 1)]
void ComputeSctrRadianceCS(uint3 ThreadId : SV_DispatchThreadID)
{
// Get attributes for the current point
float4 f4LUTCoords = LUTCoordsFromThreadID(ThreadId);
float fAltitude, fCosViewZenithAngle, fCosSunZenithAngle, fCosSunViewAngle;
InsctrLUTCoords2WorldParams(f4LUTCoords,
g_MediaParams.fEarthRadius,
g_MediaParams.fAtmBottomAltitude,
g_MediaParams.fAtmTopAltitude,
fAltitude,
fCosViewZenithAngle,
fCosSunZenithAngle,
fCosSunViewAngle );
float3 f3EarthCentre = float3(0.0, -g_MediaParams.fEarthRadius, 0.0);
float3 f3RayStart = float3(0.0, fAltitude, 0.0);
float3 f3ViewDir = ComputeViewDir(fCosViewZenithAngle);
float3 f3DirOnLight = ComputeLightDir(f3ViewDir, fCosSunZenithAngle, fCosSunViewAngle);
// Compute particle density scale factor
float2 f2ParticleDensity = exp( -float2(fAltitude, fAltitude) * g_MediaParams.f4ParticleScaleHeight.zw );
float3 f3SctrRadiance = float3(0.0, 0.0, 0.0);
// Go through a number of samples randomly distributed over the sphere
for(int iSample = 0; iSample < NUM_RANDOM_SPHERE_SAMPLES; ++iSample)
{
// Get random direction
float3 f3RandomDir = normalize( g_tex2DSphereRandomSampling.Load(int3(iSample,0,0)) );
// Get the previous order in-scattered light when looking in direction f3RandomDir (the light thus goes in direction -f3RandomDir)
float4 f4UVWQ = float4(-1.0, -1.0, -1.0, -1.0);
float3 f3PrevOrderSctr = LookUpPrecomputedScattering(
f3RayStart,
f3RandomDir,
f3EarthCentre,
g_MediaParams.fEarthRadius,
f3DirOnLight.xyz,
g_MediaParams.fAtmBottomAltitude,
g_MediaParams.fAtmTopAltitude,
g_tex3DPreviousSctrOrder,
g_tex3DPreviousSctrOrder_sampler,
f4UVWQ);
// Apply phase functions for each type of particles
// Note that total scattering coefficients are baked into the angular scattering coeffs
float3 f3DRlghInsctr = f2ParticleDensity.x * f3PrevOrderSctr;
float3 f3DMieInsctr = f2ParticleDensity.y * f3PrevOrderSctr;
float fCosTheta = dot(f3ViewDir, f3RandomDir);
ApplyPhaseFunctions(f3DRlghInsctr, f3DMieInsctr, fCosTheta);
f3SctrRadiance += f3DRlghInsctr + f3DMieInsctr;
}
// Since we tested N random samples, each sample covered 4*Pi / N solid angle
// Note that our phase function is normalized to 1 over the sphere. For instance,
// uniform phase function would be p(theta) = 1 / (4*Pi).
// Notice that for uniform intensity I if we get N samples, we must obtain exactly I after
// numeric integration
f3SctrRadiance *= 4.0*PI / float(NUM_RANDOM_SPHERE_SAMPLES);
g_rwtex3DSctrRadiance[ThreadId] = f3SctrRadiance;
}
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