KSG-Framework/DX12TLAS.cpp

#include "DX12TLAS.h"

#include "DX12CommandQueue.h"

Framework::DX12TLAS::DX12TLAS(
    ID3D12Device5* zDevice, Framework::DX12DirectCommandQueue* zDirectQueue)
    : ReferenceCounter(),
      scratchBuffer(0),
      resultBuffer(0),
      descriptorBuffer(0),
      previousResultBuffer(0),
      zDevice(zDevice),
      zDirectQueue(zDirectQueue),
      overflowInstanceIterator(0, 0, 0, 0),
      currentInstanceIndex(0),
      lastInstanceCount(0),
      mappedDescriptorBuffer(0)
{}

Framework::DX12TLAS::~DX12TLAS()
{
    if (scratchBuffer)
    {
        scratchBuffer->release();
    }
    if (resultBuffer)
    {
        resultBuffer->release();
    }
    if (descriptorBuffer)
    {
        descriptorBuffer->release();
    }
    if (previousResultBuffer)
    {
        previousResultBuffer->release();
    }
    for (const D3D12_RAYTRACING_INSTANCE_DESC* desc : overflowInstanceDescs)
    {
        delete desc;
    }
}

void Framework::DX12TLAS::startUpdate()
{
    currentInstanceIndex = -1;
    if (descriptorBuffer)
    {
        descriptorBuffer->zBuffer()->Map(0, 0, (void**)&mappedDescriptorBuffer);
    }
    else
    {
        mappedDescriptorBuffer = 0;
    }
    overflowInstanceIterator = overflowInstanceDescs.begin();
}

D3D12_RAYTRACING_INSTANCE_DESC* Framework::DX12TLAS::nextInstanceDesc()
{
    currentInstanceIndex++;
    if (mappedDescriptorBuffer
        && currentInstanceIndex < descriptorBuffer->getElementCount())
    {
        return mappedDescriptorBuffer + currentInstanceIndex;
    }
    else if (overflowInstanceIterator)
    {
        return *overflowInstanceIterator++;
    }
    else
    {
        D3D12_RAYTRACING_INSTANCE_DESC* desc
            = new D3D12_RAYTRACING_INSTANCE_DESC();
        overflowInstanceDescs.add(desc);
        return desc;
    }
}

void Framework::DX12TLAS::endUpdate()
{
    if (currentInstanceIndex < 0) // at least one instance ust be added
    {
        D3D12_RAYTRACING_INSTANCE_DESC* desc = nextInstanceDesc();
        desc->InstanceContributionToHitGroupIndex = 0;
        desc->InstanceID = 0;
        desc->Flags = D3D12_RAYTRACING_INSTANCE_FLAG_NONE;
        desc->AccelerationStructure = 0;
        desc->InstanceMask = 0; // Mark unused instances with a mask of 0
    }
    if (descriptorBuffer)
    {
        while (currentInstanceIndex < lastInstanceCount - 1)
        {
            D3D12_RAYTRACING_INSTANCE_DESC* desc = nextInstanceDesc();
            desc->InstanceMask = 0; // Mark unused instances with a mask of 0
        }
        descriptorBuffer->zBuffer()->Unmap(0, nullptr);
    }
    mappedDescriptorBuffer = 0;
    if (!descriptorBuffer || currentInstanceIndex >= lastInstanceCount)
    {
        // recalculate the size of the descriptor buffer and reallocate it
        D3D12_BUILD_RAYTRACING_ACCELERATION_STRUCTURE_INPUTS
        prebuildDesc = {};
        prebuildDesc.Type
            = D3D12_RAYTRACING_ACCELERATION_STRUCTURE_TYPE_TOP_LEVEL;
        prebuildDesc.DescsLayout = D3D12_ELEMENTS_LAYOUT_ARRAY;
        prebuildDesc.NumDescs = (unsigned)currentInstanceIndex + 1;
        prebuildDesc.Flags
            = D3D12_RAYTRACING_ACCELERATION_STRUCTURE_BUILD_FLAG_ALLOW_UPDATE;

        D3D12_RAYTRACING_ACCELERATION_STRUCTURE_PREBUILD_INFO info = {};

        zDevice->GetRaytracingAccelerationStructurePrebuildInfo(
            &prebuildDesc, &info);

        // create new buffers witch fit the TLAS
        if (resultBuffer)
        {
            if (previousResultBuffer)
            {
                previousResultBuffer->release();
            }
            previousResultBuffer = resultBuffer;
        }
        resultBuffer = new DX12Buffer(1,
            zDevice,
            dynamic_cast<DX12CommandQueue*>(zDirectQueue->getThis()),
            D3D12_RESOURCE_FLAG_ALLOW_UNORDERED_ACCESS);
        resultBuffer->setLength(
            ROUND_UP_POWER_OF_2(info.ResultDataMaxSizeInBytes, 256));
        resultBuffer->createBufferWithoutData(
            D3D12_RESOURCE_STATE_RAYTRACING_ACCELERATION_STRUCTURE);
        resultBuffer->zBuffer()->SetName(L"TLAS Result Buffer");
        if (!scratchBuffer)
        {
            scratchBuffer = new DX12Buffer(1,
                zDevice,
                dynamic_cast<DX12CommandQueue*>(zDirectQueue->getThis()),
                D3D12_RESOURCE_FLAG_ALLOW_UNORDERED_ACCESS);
        }
        scratchBuffer->setLength(
            ROUND_UP_POWER_OF_2(info.ScratchDataSizeInBytes, 256));
        scratchBuffer->createBufferWithoutData(
            D3D12_RESOURCE_STATE_UNORDERED_ACCESS);
        scratchBuffer->zBuffer()->SetName(L"TLAS Scratch Buffer");
        ID3D12Resource* oldDescriptorBuffer
            = descriptorBuffer ? descriptorBuffer->zBuffer() : 0;
        __int64 oldDescriptorBufferElementCount
            = descriptorBuffer ? descriptorBuffer->getElementCount() : 0;
        if (oldDescriptorBuffer)
        {
            oldDescriptorBuffer->AddRef();
            oldDescriptorBuffer->Map(0, 0, (void**)&mappedDescriptorBuffer);
        }
        if (!descriptorBuffer)
        {
            descriptorBuffer
                = new DX12Buffer(sizeof(D3D12_RAYTRACING_INSTANCE_DESC),
                    zDevice,
                    dynamic_cast<DX12CommandQueue*>(zDirectQueue->getThis()),
                    D3D12_RESOURCE_FLAG_NONE);
        }
        descriptorBuffer->setLength(ROUND_UP_POWER_OF_2(
            (currentInstanceIndex + 1) * sizeof(D3D12_RAYTRACING_INSTANCE_DESC),
            256));
        descriptorBuffer->createBufferWithoutData(
            D3D12_RESOURCE_STATE_GENERIC_READ, D3D12_HEAP_TYPE_UPLOAD);
        D3D12_RAYTRACING_INSTANCE_DESC* newMappedDescriptorBuffer = 0;

        // copy the old and new instance descriptions to the new buffer
        descriptorBuffer->zBuffer()->Map(
            0, 0, (void**)&newMappedDescriptorBuffer);
        if (mappedDescriptorBuffer)
        {
            memcpy(newMappedDescriptorBuffer,
                mappedDescriptorBuffer,
                oldDescriptorBufferElementCount);
            D3D12_RANGE range = {0, 0}; // do not write to the old buffer
            oldDescriptorBuffer->Unmap(0, &range);
            oldDescriptorBuffer->Release();
        }
        overflowInstanceIterator = overflowInstanceDescs.begin();
        for (__int64 i = oldDescriptorBufferElementCount;
            i <= currentInstanceIndex;
            i++)
        {
            memcpy(newMappedDescriptorBuffer + i,
                overflowInstanceIterator.val(),
                sizeof(D3D12_RAYTRACING_INSTANCE_DESC));
            overflowInstanceIterator++;
        }
        descriptorBuffer->zBuffer()->Unmap(0, nullptr);
    }
    D3D12_BUILD_RAYTRACING_ACCELERATION_STRUCTURE_DESC buildDesc = {};
    buildDesc.Inputs.Type
        = D3D12_RAYTRACING_ACCELERATION_STRUCTURE_TYPE_TOP_LEVEL;
    buildDesc.Inputs.DescsLayout = D3D12_ELEMENTS_LAYOUT_ARRAY;
    buildDesc.Inputs.InstanceDescs
        = descriptorBuffer->zBuffer()->GetGPUVirtualAddress();
    buildDesc.Inputs.NumDescs = (unsigned)currentInstanceIndex + 1;
    buildDesc.DestAccelerationStructureData
        = {resultBuffer->zBuffer()->GetGPUVirtualAddress()};
    buildDesc.ScratchAccelerationStructureData
        = {scratchBuffer->zBuffer()->GetGPUVirtualAddress()};
    buildDesc.SourceAccelerationStructureData
        = previousResultBuffer
            ? previousResultBuffer->zBuffer()->GetGPUVirtualAddress()
            : 0;
    buildDesc.Inputs.Flags
        = previousResultBuffer
            ? D3D12_RAYTRACING_ACCELERATION_STRUCTURE_BUILD_FLAG_PERFORM_UPDATE
            : D3D12_RAYTRACING_ACCELERATION_STRUCTURE_BUILD_FLAG_ALLOW_UPDATE;

    // Build the top-level AS
    zDirectQueue->zCommandList()->BuildRaytracingAccelerationStructure(
        &buildDesc, 0, nullptr);

    // Wait for the builder to complete by setting a barrier on the resulting
    // buffer. This can be important in case the rendering is triggered
    // immediately afterwards, without executing the command list
    D3D12_RESOURCE_BARRIER uavBarrier;
    uavBarrier.Type = D3D12_RESOURCE_BARRIER_TYPE_UAV;
    uavBarrier.UAV.pResource = resultBuffer->zBuffer();
    uavBarrier.Flags = D3D12_RESOURCE_BARRIER_FLAG_NONE;
    zDirectQueue->zCommandList()->ResourceBarrier(1, &uavBarrier);
    lastInstanceCount = currentInstanceIndex + 1;
}

Framework::DX12Buffer* Framework::DX12TLAS::zResultBuffer() const
{
    return resultBuffer;
}