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add light identity resolve to fix sparse reuse problem #44

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3d37742
add light identity resolve to fix sparse reuse problem
DQLin Sep 1, 2026
eaebfab
shrink light identity size from 64 bit to 32 bit
DQLin Sep 4, 2026
8361620
update the temporal MIS fallback behavior for sparse mode
DQLin Sep 10, 2026
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100 changes: 69 additions & 31 deletions rtxdi-sdk/include/rtxdi/ResamplingFunctions.slangh
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,7 @@ bool RTXDI_StreamSample(
reservoir.portalIdx = uint8_t(portalIndex);
reservoir.uv = uv;
reservoir.targetPdf = targetPdf;
reservoir.lightIdentity = RAB_UseLightIdentityResolution() ? RAB_GetLightIdentity(uint16_t(lightIndex)) : 0u;
}

return selectSample;
Expand Down Expand Up @@ -87,6 +88,7 @@ bool RTXDI_CombineReservoirs(
reservoir.portalIdx = newReservoir.portalIdx;
reservoir.uv = newReservoir.uv;
reservoir.targetPdf = targetPdf;
reservoir.lightIdentity = newReservoir.lightIdentity;
}

return selectSample;
Expand Down Expand Up @@ -330,6 +332,7 @@ RTXDI_Reservoir RTXDI_SampleSingleLight(
state.uv = lightUV;
state.targetPdf = targetPdf;
state.M = 1;
state.lightIdentity = (targetPdf > 0 && RAB_UseLightIdentityResolution()) ? RAB_GetLightIdentity(lightIdx) : 0u;

if (testVisibility)
{
Expand Down Expand Up @@ -485,6 +488,8 @@ void RTXDI_TemporalResampling(
// calculate targetPdf for the old sample
bool selectedPreviousSample = false;
uint previousM = 0;
bool useStoredTemporalTargetPdf = false;
float storedTemporalTargetPdf = 0.0f;
if (prevPixelID.x >= 0)
{
RTXDI_Reservoir prevReservoir = RAB_LoadReservoir(prevPixelID, tparams.sourceBufferIndex);
Expand All @@ -493,17 +498,25 @@ void RTXDI_TemporalResampling(

// Save the light index in the previous frame context
const uint16_t originalPrevLightIdx = prevReservoir.lightIdx;

uint16_t mappedLightID = RAB_TranslateLightIndex(prevReservoir.lightIdx, /* currentToPrevious = */ false);
if (mappedLightID == RTXDI_INVALID_LIGHT_INDEX)

// Map the previous reservoir's stored light index to the current frame.
bool prevReservoirValid;
if (RAB_UseLightIdentityResolution())
{
// Kill the reservoir
prevReservoir.weightSum = 0;
prevReservoir.lightIdx = RTXDI_INVALID_LIGHT_INDEX;
prevReservoirValid = RAB_ResolveReservoirLightIndex(prevReservoir);
}
else

@YaobinOuyang YaobinOuyang Sep 9, 2026

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So the light identity match and light index translation cannot work at the same time? I see if else structure here.

@DQLin DQLin Sep 9, 2026

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Yes. There is actually a light index translation inside RAB_ResolveReservoirLightIndex as a backup case for dynamic lights (because the hash is position-dependent). The main reason that a if-else is used here is that we don't know which reservoirs were active last frame. So we cannot guarantee that translate light index gives correct result.

{
const uint16_t mappedLightID = RAB_TranslateLightIndex(prevReservoir.lightIdx, /* currentToPrevious = */ false);
prevReservoir.lightIdx = mappedLightID;
prevReservoirValid = (mappedLightID != RTXDI_INVALID_LIGHT_INDEX);
}

if (!prevReservoirValid)
{
// The light this reservoir referenced no longer exists: kill the reservoir.
prevReservoir.weightSum = 0;
prevReservoir.lightIdx = RTXDI_INVALID_LIGHT_INDEX;
}

float weightAtCurrent = 0;
Expand All @@ -527,7 +540,17 @@ void RTXDI_TemporalResampling(
selectedPreviousSample = RTXDI_CombineReservoirs(state, prevReservoir, RAB_GetNextRandom(rng), weightAtCurrent);
if (selectedPreviousSample)
{
selectedLightPrevIdx = originalPrevLightIdx;
if (!RAB_UseLightIdentityResolution())
{
selectedLightPrevIdx = originalPrevLightIdx;
}
else
{
// Reuse the reservoir's stored targetPdf as the temporal MIS target
// This is more stable when reservoirs are not updated every frame
useStoredTemporalTargetPdf = true;
storedTemporalTargetPdf = prevReservoir.targetPdf;
}
}
}

Expand All @@ -538,44 +561,54 @@ void RTXDI_TemporalResampling(
float piSum = state.targetPdf * initialM;

if(RTXDI_IsValidReservoir(state) &&
selectedLightPrevIdx != RTXDI_INVALID_LIGHT_INDEX &&
(selectedLightPrevIdx != RTXDI_INVALID_LIGHT_INDEX || useStoredTemporalTargetPdf) &&
previousM > 0)
{
float temporalP = 0;
RAB_Surface temporalSurface = RAB_GetSurfaceForTemporalBiasCorrection(surface, prevPixelID, prevNormal, tparams.virtualMotionVector);
float temporalP;

RAB_Surface virtualTemporalSurface = temporalSurface;
#if !RTXDI_NO_PORTALS
if (state.portalIdx != RTXDI_INVALID_PORTAL_INDEX)
if (useStoredTemporalTargetPdf)
{
RAB_TransformSurface(virtualTemporalSurface, RAB_GetPortalTransform(state.portalIdx));
// the previous-frame light buffer can't be indexed with its stored index,
// so use the reservoir's stored target as the selected sample's target in the temporal domain.
temporalP = storedTemporalTargetPdf;
}
else
{
RAB_Surface temporalSurface = RAB_GetSurfaceForTemporalBiasCorrection(surface, prevPixelID, prevNormal, tparams.virtualMotionVector);

RAB_Surface virtualTemporalSurface = temporalSurface;
#if !RTXDI_NO_PORTALS
if (state.portalIdx != RTXDI_INVALID_PORTAL_INDEX)

@YaobinOuyang YaobinOuyang Sep 9, 2026

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The portal handling code should be independent from the multiple frame light ID match code. What it's doing here is to calculate the virtual surface with respect to portal space. It's still needed when you are matching light ID across multiple frames.

{
RAB_TransformSurface(virtualTemporalSurface, RAB_GetPortalTransform(state.portalIdx));
}
#endif

RAB_LightSample selectedSampleAtTemporalSurface = RAB_GetLightSample(selectedLightPrevIdx,
state.uv, virtualTemporalSurface, /* usePreviousLights = */ true);
RAB_LightSample selectedSampleAtTemporalSurface = RAB_GetLightSample(selectedLightPrevIdx,
state.uv, virtualTemporalSurface, /* usePreviousLights = */ true);

temporalP = RAB_GetLightSampleTargetPdfForSurface(selectedSampleAtTemporalSurface, virtualTemporalSurface);
temporalP = RAB_GetLightSampleTargetPdfForSurface(selectedSampleAtTemporalSurface, virtualTemporalSurface);

// If we have selected the temporal sample and discard is enabled, we know that the sample was visible
// on the previous frame because otherwise it would've been discarded and we couldn't select it.
// In practice, temporal samples are selected way more often than new samples, which means this
// condition culls the vast majority of visibility rays here.
const bool selectedSampleKnownVisible = selectedPreviousSample && tparams.discardInvisibleSamples;
// If we have selected the temporal sample and discard is enabled, we know that the sample was visible
// on the previous frame because otherwise it would've been discarded and we couldn't select it.
// In practice, temporal samples are selected way more often than new samples, which means this
// condition culls the vast majority of visibility rays here.
const bool selectedSampleKnownVisible = selectedPreviousSample && tparams.discardInvisibleSamples;

if (temporalP > 0 && tparams.biasCorrectionMode >= RTXDI_BIAS_CORRECTION_RAY_TRACED && !selectedSampleKnownVisible)
{
float3 attenuation;
if (temporalP > 0 && tparams.biasCorrectionMode >= RTXDI_BIAS_CORRECTION_RAY_TRACED && !selectedSampleKnownVisible)
{
float3 attenuation;
#if RTXDI_NO_PORTALS
bool sampleVisible = RAB_TraceLightSampleVisibility(temporalSurface, selectedSampleAtTemporalSurface,
RTXDI_INVALID_PORTAL_INDEX, false, false, true, attenuation);
bool sampleVisible = RAB_TraceLightSampleVisibility(temporalSurface, selectedSampleAtTemporalSurface,
RTXDI_INVALID_PORTAL_INDEX, false, false, true, attenuation);
#else
bool sampleVisible = RAB_TraceLightSampleVisibility(temporalSurface, selectedSampleAtTemporalSurface,
state.portalIdx, false, false, true, attenuation);
bool sampleVisible = RAB_TraceLightSampleVisibility(temporalSurface, selectedSampleAtTemporalSurface,
state.portalIdx, false, false, true, attenuation);
#endif

if (!sampleVisible)
temporalP = 0;
if (!sampleVisible)
temporalP = 0;
}
}

pi = selectedPreviousSample ? temporalP : pi;
Expand Down Expand Up @@ -684,6 +717,11 @@ RTXDI_Reservoir RTXDI_SpatialResampling(

RTXDI_Reservoir neighborReservoir = RAB_LoadReservoir(neighborID, sparams.sourceBufferIndex);

if (RAB_UseLightIdentityResolution())
{
RAB_ResolveReservoirLightIndex(neighborReservoir);
}

float targetPdf = 0;
if (RTXDI_IsValidReservoir(neighborReservoir))
{
Expand Down
6 changes: 5 additions & 1 deletion rtxdi-sdk/include/rtxdi/Reservoir.slangh
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@ struct RTXDI_Reservoir
float weightSum;
float targetPdf;
uint16_t M;
uint lightIdentity;
};

RTXDI_PackedReservoir RTXDI_PackReservoir(RTXDI_Reservoir reservoir)
Expand All @@ -38,7 +39,8 @@ RTXDI_PackedReservoir RTXDI_PackReservoir(RTXDI_Reservoir reservoir)
packedReservoir.data0 = asuint(float4(reservoir.uv, reservoir.weightSum, reservoir.targetPdf));
packedReservoir.data1.x = ((uint(reservoir.lightIdx) << 16) | (reservoir.M & 0xffff));
packedReservoir.data1.y = uint(reservoir.portalIdx);
packedReservoir.data1.zw = 0;
packedReservoir.data1.z = reservoir.lightIdentity;
packedReservoir.data1.w = 0;
return packedReservoir;
}

Expand All @@ -51,6 +53,7 @@ RTXDI_Reservoir RTXDI_EmptyReservoir()
s.weightSum = 0.0f;
s.M = uint16_t(0);
s.portalIdx = RTXDI_INVALID_PORTAL_INDEX;
s.lightIdentity = 0;
return s;
}

Expand All @@ -64,6 +67,7 @@ RTXDI_Reservoir RTXDI_UnpackReservoir(RTXDI_PackedReservoir packedReservoir)
reservoir.M = uint16_t(packedReservoir.data1.x & 0xffff);

reservoir.portalIdx = uint8_t(packedReservoir.data1.y);
reservoir.lightIdentity = packedReservoir.data1.z;
return reservoir;
}

Expand Down
20 changes: 20 additions & 0 deletions rtxdi-sdk/shaders/ResamplingCompileTest.comp.slang
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Original file line number Diff line number Diff line change
Expand Up @@ -230,6 +230,26 @@ int RAB_TranslateLightIndex(uint lightIndex, bool currentToPrevious)
return -1;
}

bool RAB_UseLightIdentityResolution()
{
return false;
}

uint RAB_GetLightIdentity(uint currentLightIdx)
{
return 0;
}

uint16_t RAB_ResolveLightIndexFromIdentity(uint identity)
{
return RTXDI_INVALID_LIGHT_INDEX;
}

bool RAB_ResolveReservoirLightIndex(inout RTXDI_Reservoir reservoir)
{
return RTXDI_IsValidReservoir(reservoir);
}

bool RAB_ShouldDiscardEnlargedPixel(inout RAB_RandomSamplerState rng, RAB_Surface surface, float3 virtualMotionVector)
{
return false;
Expand Down