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void ComputeUnshadowedInscattering(float2 f2SampleLocation,
float fCamSpaceZ,
uint uiNumSteps,
float3 f3EarthCentre,
out float3 f3Inscattering,
out float3 f3Extinction)
{
f3Inscattering = float3(0.0, 0.0, 0.0);
f3Extinction = float3(1.0, 1.0, 1.0);
float3 f3RayTermination = ProjSpaceXYZToWorldSpace( float3(f2SampleLocation, fCamSpaceZ), g_CameraAttribs.mProj, g_CameraAttribs.mViewProjInv );
float3 f3CameraPos = g_CameraAttribs.f4Position.xyz;
float3 f3ViewDir = f3RayTermination - f3CameraPos;
float fRayLength = length(f3ViewDir);
f3ViewDir /= fRayLength;
float4 f4Isecs;
GetRaySphereIntersection2(f3CameraPos, f3ViewDir, f3EarthCentre,
float2(g_MediaParams.fAtmTopRadius, g_MediaParams.fAtmBottomRadius), f4Isecs);
float2 f2RayAtmTopIsecs = f4Isecs.xy;
float2 f2RayEarthIsecs = f4Isecs.zw;
if( f2RayAtmTopIsecs.y <= 0.0 )
{
// view dir
// /
// d<0 /
// *---------> *
// . . . / .
// . ' ' . . ' /\ ' .
// / f2rayatmtopisecs.y < 0
//
// the camera is outside the atmosphere and the ray either does not intersect the
// top of it or the intersection point is behind the camera. In either
// case there is no inscattering
return;
}
float3 f3RayStart = f3CameraPos + f3ViewDir * max(0.0, f2RayAtmTopIsecs.x);
if( fCamSpaceZ > g_CameraAttribs.fFarPlaneZ ) // fFarPlaneZ is pre-multiplied with 0.999999f
fRayLength = +FLT_MAX;
fRayLength = min(fRayLength, f2RayAtmTopIsecs.y);
// If there is an intersection with the Earth surface, limit the tracing distance to the intersection
if( f2RayEarthIsecs.x > 0.0 )
{
fRayLength = min(fRayLength, f2RayEarthIsecs.x);
}
float3 f3RayEnd = f3CameraPos + f3ViewDir * fRayLength;
#if SINGLE_SCATTERING_MODE == SINGLE_SCTR_MODE_INTEGRATION
IntegrateUnshadowedInscattering(f3RayStart,
f3RayEnd,
f3ViewDir,
f3EarthCentre,
g_MediaParams.fEarthRadius,
g_MediaParams.fAtmBottomAltitude,
g_MediaParams.fAtmAltitudeRangeInv,
g_MediaParams.f4ParticleScaleHeight,
-g_LightAttribs.f4Direction.xyz,
uiNumSteps,
f3Inscattering,
f3Extinction);
#endif
#if SINGLE_SCATTERING_MODE == SINGLE_SCTR_MODE_LUT || MULTIPLE_SCATTERING_MODE > MULTIPLE_SCTR_MODE_NONE
#if MULTIPLE_SCATTERING_MODE > MULTIPLE_SCTR_MODE_NONE
#if SINGLE_SCATTERING_MODE == SINGLE_SCTR_MODE_LUT
#define tex3DSctrLUT g_tex3DMultipleSctrLUT
#define tex3DSctrLUT_sampler g_tex3DMultipleSctrLUT_sampler
#elif SINGLE_SCATTERING_MODE == SINGLE_SCTR_MODE_NONE || SINGLE_SCATTERING_MODE == SINGLE_SCTR_MODE_INTEGRATION
#define tex3DSctrLUT g_tex3DHighOrderSctrLUT
#define tex3DSctrLUT_sampler g_tex3DHighOrderSctrLUT_sampler
#endif
#else
#define tex3DSctrLUT g_tex3DSingleSctrLUT
#define tex3DSctrLUT_sampler g_tex3DSingleSctrLUT_sampler
#endif
f3Extinction = GetExtinctionUnverified(f3RayStart, f3RayEnd, f3ViewDir, f3EarthCentre, g_MediaParams.fEarthRadius, g_MediaParams.f4ParticleScaleHeight);
// To avoid artifacts, we must be consistent when performing look-ups into the scattering texture, i.e.
// we must assure that if the first look-up is above (below) horizon, then the second look-up
// is also above (below) horizon.
float4 f4UVWQ = float4(-1.0, -1.0, -1.0, -1.0);
f3Inscattering +=
LookUpPrecomputedScattering(
f3RayStart,
f3ViewDir,
f3EarthCentre,
g_MediaParams.fEarthRadius,
-g_LightAttribs.f4Direction.xyz,
g_MediaParams.fAtmBottomAltitude,
g_MediaParams.fAtmTopAltitude,
tex3DSctrLUT,
tex3DSctrLUT_sampler,
f4UVWQ);
// Provide previous look-up coordinates to the function to assure that look-ups are consistent
f3Inscattering -= f3Extinction *
LookUpPrecomputedScattering(
f3RayEnd,
f3ViewDir,
f3EarthCentre,
g_MediaParams.fEarthRadius,
-g_LightAttribs.f4Direction.xyz,
g_MediaParams.fAtmBottomAltitude,
g_MediaParams.fAtmTopAltitude,
tex3DSctrLUT,
tex3DSctrLUT_sampler,
f4UVWQ);
#undef tex3DSctrLUT
#undef tex3DSctrLUT_sampler
#endif
}
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