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perf(SSGI): eliminate radiance copy via direct UAV write #2127

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Merged
doodlum merged 1 commit into from
Apr 16, 2026
Merged

perf(SSGI): eliminate radiance copy via direct UAV write #2127

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38 changes: 22 additions & 16 deletions src/Features/ScreenSpaceGI.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -403,7 +403,7 @@ void ScreenSpaceGI::SetupResources()
{
texRadiance = eastl::make_unique<Texture2D>(texDesc);
texRadiance->CreateSRV(srvDesc);
texRadiance->CreateUAV(uavDesc); // Create default UAV for mip 0
// No default UAV needed: prefilterRadiance binds per-mip UAVs via uavRadiance[].

// Create individual UAVs for each mip level for prefiltering
for (uint i = 0; i < 5; ++i) {
Expand All @@ -415,10 +415,12 @@ void ScreenSpaceGI::SetupResources()
DX::ThrowIfFailed(device->CreateUnorderedAccessView(texRadiance->resource.get(), &mipUavDesc, uavRadiance[i].put()));
}

// Create temporary texture for prefiltering (single mip level, used as SRV input)
// Staging texture for mip 0 radiance. radianceDisocc writes it directly,
// prefilterRadiance reads it as SRV and writes the mip chain back to texRadiance.
// Avoids a full-texture CopySubresourceRegion each frame.
D3D11_TEXTURE2D_DESC tempTexDesc = texDesc;
tempTexDesc.MipLevels = 1;
tempTexDesc.BindFlags = D3D11_BIND_SHADER_RESOURCE | D3D11_BIND_RENDER_TARGET;
tempTexDesc.BindFlags = D3D11_BIND_SHADER_RESOURCE | D3D11_BIND_UNORDERED_ACCESS;

D3D11_SHADER_RESOURCE_VIEW_DESC tempSrvDesc = {
.Format = DXGI_FORMAT_R11G11B10_FLOAT,
Expand All @@ -428,8 +430,15 @@ void ScreenSpaceGI::SetupResources()
.MipLevels = 1 }
};

D3D11_UNORDERED_ACCESS_VIEW_DESC tempUavDesc = {
.Format = DXGI_FORMAT_R11G11B10_FLOAT,
.ViewDimension = D3D11_UAV_DIMENSION_TEXTURE2D,
.Texture2D = { .MipSlice = 0 }
};

texRadianceTemp = eastl::make_unique<Texture2D>(tempTexDesc);
texRadianceTemp->CreateSRV(tempSrvDesc);
texRadianceTemp->CreateUAV(tempUavDesc);
}

texDesc.BindFlags &= ~D3D11_BIND_RENDER_TARGET;
Expand Down Expand Up @@ -774,7 +783,7 @@ void ScreenSpaceGI::DrawSSGI()
srvs.at(9) = texGiSpecular[inputAoTexIdx]->srv.get();
srvs.at(10) = nullptr;

uavs.at(0) = texRadiance->uav.get();
uavs.at(0) = texRadianceTemp->uav.get();
uavs.at(1) = texAccumFrames[!lastFrameAccumTexIdx]->uav.get();
uavs.at(2) = texAo[!inputAoTexIdx]->uav.get();
uavs.at(3) = texIlY[!inputGITexIdx]->uav.get();
Expand All @@ -786,22 +795,19 @@ void ScreenSpaceGI::DrawSSGI()
context->CSSetShader(radianceDisoccCompute.get(), nullptr, 0);
context->Dispatch((internalRes[0] + 7u) >> 3, (internalRes[1] + 7u) >> 3, 1);

// Prefilter radiance texture instead of using GenerateMips for proper dynamic resolution handling
// Prefilter radiance texture instead of using GenerateMips for proper dynamic resolution handling.
// radianceDisocc wrote mip 0 directly to texRadianceTemp above, so we can bind it
// as SRV input here without an intermediate CopySubresourceRegion.
{
TracyD3D11Zone(globals::state->tracyCtx, "SSGI - Prefilter Radiance");

// First copy mip 0 from radiance to temporary texture to avoid read/write conflict
context->CopySubresourceRegion(
texRadianceTemp->resource.get(), 0, 0, 0, 0,
texRadiance->resource.get(), 0, nullptr);

resetViews();
srvs.at(0) = texRadianceTemp->srv.get(); // Use temporary texture as input
uavs.at(0) = uavRadiance[0].get(); // Mip 0
uavs.at(1) = uavRadiance[1].get(); // Mip 1
uavs.at(2) = uavRadiance[2].get(); // Mip 2
uavs.at(3) = uavRadiance[3].get(); // Mip 3
uavs.at(4) = uavRadiance[4].get(); // Mip 4
srvs.at(0) = texRadianceTemp->srv.get();
uavs.at(0) = uavRadiance[0].get(); // Mip 0
uavs.at(1) = uavRadiance[1].get(); // Mip 1
uavs.at(2) = uavRadiance[2].get(); // Mip 2
uavs.at(3) = uavRadiance[3].get(); // Mip 3
uavs.at(4) = uavRadiance[4].get(); // Mip 4

context->CSSetShaderResources(0, 1, srvs.data());
context->CSSetUnorderedAccessViews(0, 5, uavs.data(), nullptr);
Expand Down
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