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Improve the quality of volumetric lighting reprojection

/main
Evgenii Golubev 7 年前
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17d8f4ec
共有 1 个文件被更改，包括 64 次插入 和 67 次删除
  1. 131
      ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/VolumetricLighting.compute

131
ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/VolumetricLighting.compute
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#define VBUFFER_SLICE_COUNT 128
#endif
#define SUPPORT_ASYMMETRY 1 // Support asymmetric phase functions
#define SUPPORT_PUNCTUAL_LIGHTS 1 // Punctual lights contribute to fog lighting
#define GROUP_SIZE_1D 8

// Implementation
//--------------------------------------------------------------------------------------------------
// A ray with a single origin and two directions:
// one pointing at the center of the voxel, and one jittered in screen space.
float3 strataDirWS; // Normalized, tile-stratified
float3 centerDirWS; // Normalized, tile-centered
float strataDirInvViewZ; // 1 / ViewSpace(strataDirWS).z
float twoDirRatioViewZ; // ViewSpace(strataDirWS).z / ViewSpace(centerDirWS).z
float3 jitterDirWS; // Normalized, voxel-jittered in the screen space
float3 centerDirWS; // Normalized, voxel-centered in the screen space
float jitterDirInvViewZ; // 1 / ViewSpace(jitterDirWS).z
float twoDirRatioViewZ; // ViewSpace(jitterDirWS).z / ViewSpace(centerDirWS).z
// Returns a point along the stratified direction.
float ConvertLinearDepthToJitterRayDist(DualRay ray, float z)
{
return z * ray.jitterDirInvViewZ;
}
float ConvertJitterDistToCenterRayDist(DualRay ray, float t)
{
return t * ray.twoDirRatioViewZ;
}
// Returns a point along the jittered direction.
return ray.originWS + t * ray.strataDirWS;
return ray.originWS + t * ray.jitterDirWS;
// Returns a point along the centered direction. It has a special property:
// ViewSpace(GetPointAtDistance(ray, t)).z = ViewSpace(GetCenterAtDistance(ray, t)).z,
// e.i. both points computed from the same value of 't' reside on the same Z-plane in the view space.
float3 GetCenterAtDistance(DualRay ray, float t)
// Returns a point along the centered direction.
float3 GetCenterAtDistance(DualRay ray, float s)
t *= ray.twoDirRatioViewZ; // Perform the Z-coordinate conversion
return ray.originWS + t * ray.centerDirWS;
return ray.originWS + s * ray.centerDirWS;
}
struct VoxelLighting

color, attenuation);
// Important:
// Ideally, all scattering calculations should use the stratified versions
// Ideally, all scattering calculations should use the jittered versions
// of the sample position and the ray direction. However, correct reprojection
// of asymmetrically scattered lighting (affected by an anisotropic phase
// function) is not possible. We work around this issue by reprojecting

float3 coneAxisX = lenMul * light.right;
float3 coneAxisY = lenMul * light.up;
sampleLight = IntersectRayCone(ray.originWS, ray.strataDirWS,
sampleLight = IntersectRayCone(ray.originWS, ray.jitterDirWS,
light.positionWS, light.forward,
coneAxisX, coneAxisY,
t0, t1, tEntr, tExit);

float t, distSq, rcpPdf;
ImportanceSamplePunctualLight(rndVal, light.positionWS,
ray.originWS, ray.strataDirWS,
ray.originWS, ray.jitterDirWS,
tEntr, tExit, t, distSq, rcpPdf,
hackMinDistSq);

0, L, lightToSample, distances, color, attenuation);
// Important:
// Ideally, all scattering calculations should use the stratified versions
// Ideally, all scattering calculations should use the jittered versions
// of the sample position and the ray direction. However, correct reprojection
// of asymmetrically scattered lighting (affected by an anisotropic phase
// function) is not possible. We work around this issue by reprojecting

float3x3 rotMat = float3x3(light.right, light.up, light.forward);
float3 o = mul(rotMat, ray.originWS - light.positionWS);
float3 d = mul(rotMat, ray.strataDirWS);
float3 d = mul(rotMat, ray.jitterDirWS);
float range = light.size.x;
float3 boxPt0 = float3(-1, -1, 0);

0, L, lightToSample, distances, color, attenuation);
// Important:
// Ideally, all scattering calculations should use the stratified versions
// Ideally, all scattering calculations should use the jittered versions
// of the sample position and the ray direction. However, correct reprojection
// of asymmetrically scattered lighting (affected by an anisotropic phase
// function) is not possible. We work around this issue by reprojecting

void FillVolumetricLightingBuffer(LightLoopContext context, uint featureFlags,
PositionInputs posInput, DualRay ray)
{
float n = _VBufferDepthDecodingParams.x + _VBufferDepthDecodingParams.z;
float z0 = n; // Start integration from the near plane
float t0 = ray.strataDirInvViewZ * z0; // Convert view space Z to distance along the stratified ray
float de = rcp(VBUFFER_SLICE_COUNT); // Log-encoded distance between slices
const float n = _VBufferDepthDecodingParams.x + _VBufferDepthDecodingParams.z;
const float z0 = n; // Start integration from the near plane
const float de = rcp(VBUFFER_SLICE_COUNT); // Log-encoded distance between slices
float t0 = ConvertLinearDepthToJitterRayDist(ray, z0);
// The contribution of the ambient probe does not depend on the position,
// only on the direction and the length of the interval.

uint3 voxelCoord = uint3(posInput.positionSS, slice);
float e1 = slice * de + de; // (slice + 1) / sliceCount
#if defined(SHADER_API_METAL)
// Warning: this compiles, but it's nonsense. Use DecodeLogarithmicDepthGeneralized().
float z1 = DecodeLogarithmicDepth(e1, _VBufferDepthDecodingParams);
#else
#endif
float t1 = ray.strataDirInvViewZ * z1; // Convert view space Z to distance along the stratified ray
float t1 = ConvertLinearDepthToJitterRayDist(ray, z1);
float dt = t1 - t0;
#ifdef USE_CLUSTERED_LIGHTLIST

// Compute the -exact- position of the center of the voxel.
// It's important since the accumulated value of the integral is stored at the center.
// We will use it for participating media sampling, asymmetric scattering and reprojection.
float tc = t0 + 0.5 * dt;
float3 centerWS = GetCenterAtDistance(ray, tc);
float s = ConvertJitterDistToCenterRayDist(ray, t0 + 0.5 * dt);
float3 centerWS = GetCenterAtDistance(ray, s);
// Sample the participating medium at 'tc' (or 'centerWS').
// Sample the participating medium at the center of the voxel.
// We consider it to be constant along the interval [t0, t1] (within the voxel).
// TODO: piecewise linear.
float3 scattering = LOAD_TEXTURE3D(_VBufferDensity, voxelCoord).rgb;

);
#endif
#if ENABLE_REPROJECTION
// Reproject the history at 'centerWS'.
float4 reprojValue = SampleVBuffer(TEXTURE3D_PARAM(_VBufferLightingHistory, s_linear_clamp_sampler),
centerWS,

// TODO: doesn't seem to be worth it, removed for now.
// Perform temporal blending.
// Both radiance values are obtained by integrating over line segments of different length.
// Blending only makes sense if the length of both intervals is the same.
// Therefore, the reprojected radiance needs to be rescaled by (frame_dt / reproj_dt).
// Both radiance values are obtained by integrating over line segments of different length,
// with potentially different participating media coverage.
// Blending only makes sense if the voxels are virtually identical.
// Therefore, we need to rescale the history to make it match the current configuration.
// In order to do that, we integrate transmittance over the length of the ray interval
// passing through the center of the voxel. The integral can be interpreted as the amount of
// isotropically in-scattered radiance from a directional light with unit intensity.
// We ignore jittering, as we want values from the same voxel to be reporojected without
// any rescaling.
float ds = ConvertJitterDistToCenterRayDist(ray, dt);
float centerTransmInt = TransmittanceIntegralHomogeneousMedium(extinction, ds);
float reprojRcpLen = reprojSuccess ? rcp(reprojValue.a) : 0;
float lengthScale = dt * reprojRcpLen;
float reprojScale = reprojSuccess ? (centerTransmInt * rcp(reprojValue.a)) : 0;
float3 blendedRadiance = (1 - blendFactor) * lighting.radianceNoPhase + blendFactor * lengthScale * reprojRadiance;
float3 blendedRadiance = (1 - blendFactor) * lighting.radianceNoPhase + blendFactor * reprojScale * reprojRadiance;
// Store the feedback for the voxel.
// TODO: dynamic lights (which update their position, rotation, cookie or shadow at runtime)

_VBufferLightingFeedback[voxelCoord] = float4(blendedRadiance, dt);
_VBufferLightingFeedback[voxelCoord] = float4(blendedRadiance, centerTransmInt);
#if SUPPORT_ASYMMETRY
#endif
#if SUPPORT_ASYMMETRY
#else
float3 blendedRadiance = lighting.radianceNoPhase;
#endif
#if SUPPORT_ASYMMETRY
float phase = _CornetteShanksConstant;
#else
float phase = IsotropicPhaseFunction();
#endif
float4 integral = float4(totalRadiance, opticalDepth);
float phase = _CornetteShanksConstant;
// Integrate the contribution of the probe over the interval.
// Integral{a, b}{Transmittance(0, t) * L_s(t) dt} = Transmittance(0, a) * Integral{a, b}{Transmittance(0, t - a) * L_s(t) dt}.

// Compute the optical depth up to the end of the interval.
opticalDepth += 0.5 * extinction * dt;
z0 = z1;
t0 = t1;
#ifdef USE_CLUSTERED_LIGHTLIST

float2 centerCoord = voxelCoord + float2(0.5, 0.5);
#if ENABLE_REPROJECTION
float2 strataCoord = centerCoord + _VBufferSampleOffset.xy;
float2 jitterCoord = centerCoord + _VBufferSampleOffset.xy;
float2 strataCoord = centerCoord;
float2 jitterCoord = centerCoord;
// Compute the (tile-centered) ray direction s.t. its ViewSpace(rayDirWS).z = 1.
// Compute the (voxel-centered in the screen space) ray direction s.t. its ViewSpace(rayDirWS).z = 1.
// Compute the (tile-stratified) ray direction s.t. its ViewSpace(rayDirWS).z = 1.
float3 strataDirWS = mul(-float3(strataCoord, 1), (float3x3)_VBufferCoordToViewDirWS);
float strataDirLenSq = dot(strataDirWS, strataDirWS);
float strataDirLenRcp = rsqrt(strataDirLenSq);
float strataDirLen = strataDirLenSq * strataDirLenRcp;
// Compute the (voxel-jittered in the screen space) ray direction s.t. its ViewSpace(rayDirWS).z = 1.
float3 jitterDirWS = mul(-float3(jitterCoord, 1), (float3x3)_VBufferCoordToViewDirWS);
float jitterDirLenSq = dot(jitterDirWS, jitterDirWS);
float jitterDirLenRcp = rsqrt(jitterDirLenSq);
float jitterDirLen = jitterDirLenSq * jitterDirLenRcp;
ray.strataDirWS = strataDirWS * strataDirLenRcp; // Normalize
ray.jitterDirWS = jitterDirWS * jitterDirLenRcp; // Normalize
ray.strataDirInvViewZ = strataDirLen; // View space Z
ray.twoDirRatioViewZ = centerDirLen * strataDirLenRcp; // View space Z ratio
ray.jitterDirInvViewZ = jitterDirLen; // View space Z
ray.twoDirRatioViewZ = centerDirLen * jitterDirLenRcp; // View space Z ratio
// TODO
LightLoopContext context;

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