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#include "AtmosphereShadersCommon.fxh"
#ifndef THREAD_GROUP_SIZE
# define THREAD_GROUP_SIZE 16
#endif
cbuffer cbParticipatingMediaScatteringParams
{
AirScatteringAttribs g_MediaParams;
}
Texture3D<float3> g_tex3DPointwiseSctrRadiance;
SamplerState g_tex3DPointwiseSctrRadiance_sampler;
#include "LookUpTables.fxh"
#include "PrecomputeCommon.fxh"
RWTexture3D</*format = rgba32f*/float3> g_rwtex3DInsctrOrder;
// This shader computes in-scattering order for a given point and direction. It performs integration of the
// light scattered at particular point along the ray, see eq. (11) in [Bruneton and Neyret 08].
[numthreads(THREAD_GROUP_SIZE, THREAD_GROUP_SIZE, 1)]
void ComputeScatteringOrderCS(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);
// Intersect the ray with the atmosphere boundaries
float4 f4Isecs;
GetRaySphereIntersection2( f3RayStart, f3ViewDir, f3EarthCentre,
float2(g_MediaParams.fAtmBottomRadius, g_MediaParams.fAtmTopRadius),
f4Isecs);
float2 f2RayEarthIsecs = f4Isecs.xy;
float2 f2RayAtmTopIsecs = f4Isecs.zw;
if(f2RayAtmTopIsecs.y <= 0.0)
{
// This is just a sanity check and should never happen
// as the start point is always under the top of the
// atmosphere (look at InsctrLUTCoords2WorldParams())
g_rwtex3DInsctrOrder[ThreadId] = float3(0.0, 0.0, 0.0);
return;
}
float fRayLength = f2RayAtmTopIsecs.y;
if(f2RayEarthIsecs.x > 0.0)
fRayLength = min(fRayLength, f2RayEarthIsecs.x);
float3 f3RayEnd = f3RayStart + f3ViewDir * fRayLength;
const int iNumSamples = 64;
float4 f4UVWQ = float4(-1.0, -1.0, -1.0, -1.0);
float3 f3PrevSctrRadiance = LookUpPrecomputedScattering(
f3RayStart,
f3ViewDir,
f3EarthCentre,
g_MediaParams.fEarthRadius,
f3DirOnLight.xyz,
g_MediaParams.fAtmBottomAltitude,
g_MediaParams.fAtmTopAltitude,
g_tex3DPointwiseSctrRadiance,
g_tex3DPointwiseSctrRadiance_sampler,
f4UVWQ);
float2 f2PrevParticleDensity = exp( -float2(fAltitude, fAltitude) * g_MediaParams.f4ParticleScaleHeight.zw );
float2 f2NetParticleDensityFromCam = float2(0.0, 0.0);
float3 f3Inscattering = float3(0.0, 0.0, 0.0);
// We want to place more samples when the starting point is close to the surface,
// but for high altitudes linear distribution works better.
float fStartAltitude = length(f3RayStart - f3EarthCentre) - g_MediaParams.fEarthRadius;
float pwr = lerp(2.0, 1.0, saturate((fStartAltitude - g_MediaParams.fAtmBottomAltitude) * g_MediaParams.fAtmAltitudeRangeInv));
float fPrevSampleDist = 0.0;
for (int iSample = 1; iSample <= iNumSamples; ++iSample)
{
// We need to place more samples closer to the start point and fewer samples farther away.
// The ad-hoc power function does the job well.
float r = pow(float(iSample) / float(iNumSamples), pwr);
float3 f3Pos = lerp(f3RayStart, f3RayEnd, r);
float fCurrSampleDist = fRayLength * r;
float fStepLen = fCurrSampleDist - fPrevSampleDist;
fPrevSampleDist = fCurrSampleDist;
float fCurrHeight = length(f3Pos - f3EarthCentre) - g_MediaParams.fEarthRadius;
float2 f2ParticleDensity = exp( -float2(fCurrHeight, fCurrHeight) * g_MediaParams.f4ParticleScaleHeight.zw );
f2NetParticleDensityFromCam += (f2PrevParticleDensity + f2ParticleDensity) * (fStepLen / 2.0);
f2PrevParticleDensity = f2ParticleDensity;
// Get optical depth
float3 f3RlghOpticalDepth = g_MediaParams.f4RayleighExtinctionCoeff.rgb * f2NetParticleDensityFromCam.x;
float3 f3MieOpticalDepth = g_MediaParams.f4MieExtinctionCoeff.rgb * f2NetParticleDensityFromCam.y;
// Compute extinction from the camera for the current integration point:
float3 f3ExtinctionFromCam = exp( -(f3RlghOpticalDepth + f3MieOpticalDepth) );
// Get attenuated scattered light radiance in the current point
float4 f4UVWQ = float4(-1.0, -1.0, -1.0, -1.0);
float3 f3SctrRadiance = f3ExtinctionFromCam *
LookUpPrecomputedScattering(
f3Pos,
f3ViewDir,
f3EarthCentre,
g_MediaParams.fEarthRadius,
f3DirOnLight.xyz,
g_MediaParams.fAtmBottomAltitude,
g_MediaParams.fAtmTopAltitude,
g_tex3DPointwiseSctrRadiance,
g_tex3DPointwiseSctrRadiance_sampler,
f4UVWQ);
// Update in-scattering integral
f3Inscattering += (f3SctrRadiance + f3PrevSctrRadiance) * (fStepLen/2.0);
f3PrevSctrRadiance = f3SctrRadiance;
}
g_rwtex3DInsctrOrder[ThreadId] = f3Inscattering;
}
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