Method buildTlas

Source/Falcor/Scene/Scene.cpp:3717–3813

    }

    void Scene::buildTlas(RenderContext* pRenderContext, uint32_t rayTypeCount, bool perMeshHitEntry)
    {
        FALCOR_PROFILE(pRenderContext, "buildTlas");

        TlasData tlas;
        auto it = mTlasCache.find(rayTypeCount);
        if (it != mTlasCache.end()) tlas = it->second;

        // Prepare instance descs.
        // Note if there are no instances, we'll build an empty TLAS.
        fillInstanceDesc(mInstanceDescs, rayTypeCount, perMeshHitEntry);

        RtAccelerationStructureBuildInputs inputs = {};
        inputs.kind = RtAccelerationStructureKind::TopLevel;
        inputs.descCount = (uint32_t)mInstanceDescs.size();
        inputs.flags = RtAccelerationStructureBuildFlags::None;

        // Add build flags for dynamic scenes if TLAS should be updating instead of rebuilt
        if ((mpAnimationController->hasAnimations() || mpAnimationController->hasAnimatedVertexCaches()) && mTlasUpdateMode == UpdateMode::Refit)
        {
            inputs.flags |= RtAccelerationStructureBuildFlags::AllowUpdate;

            // If TLAS has been built already and it was built with ALLOW_UPDATE
            if (tlas.pTlasObject != nullptr && tlas.updateMode == UpdateMode::Refit) inputs.flags |= RtAccelerationStructureBuildFlags::PerformUpdate;
        }

        tlas.updateMode = mTlasUpdateMode;

        // On first build for the scene, create scratch buffer and cache prebuild info. As long as INSTANCE_DESC count doesn't change, we can reuse these
        if (mpTlasScratch == nullptr)
        {
            // Prebuild
            mTlasPrebuildInfo = RtAccelerationStructure::getPrebuildInfo(mpDevice.get(), inputs);
            mpTlasScratch = mpDevice->createBuffer(mTlasPrebuildInfo.scratchDataSize, ResourceBindFlags::UnorderedAccess, MemoryType::DeviceLocal);
            mpTlasScratch->setName("Scene::mpTlasScratch");

            // #SCENE This isn't guaranteed according to the spec, and the scratch buffer being stored should be sized differently depending on update mode
            FALCOR_ASSERT(mTlasPrebuildInfo.updateScratchDataSize <= mTlasPrebuildInfo.scratchDataSize);
        }

        // Setup GPU buffers
        RtAccelerationStructure::BuildDesc asDesc = {};
        asDesc.inputs = inputs;

        // If first time building this TLAS
        if (tlas.pTlasObject == nullptr)
        {
            {
                // Allocate a new buffer for the TLAS only if the existing buffer isn't big enough.
                if (!tlas.pTlasBuffer || tlas.pTlasBuffer->getSize() < mTlasPrebuildInfo.resultDataMaxSize)
                {
                    tlas.pTlasBuffer = mpDevice->createBuffer(mTlasPrebuildInfo.resultDataMaxSize, ResourceBindFlags::AccelerationStructure, MemoryType::DeviceLocal);
                    tlas.pTlasBuffer->setName("Scene TLAS buffer");
                }
            }

            RtAccelerationStructure::Desc asCreateDesc = {};
            asCreateDesc.setKind(RtAccelerationStructureKind::TopLevel);