o3de/Gems/Atom/RPI/Code/Source/RPI.Reflect/Shader/ShaderAsset.cpp

/*
 * Copyright (c) Contributors to the Open 3D Engine Project.
 * For complete copyright and license terms please see the LICENSE at the root of this distribution.
 *
 * SPDX-License-Identifier: Apache-2.0 OR MIT
 *
 */
#include <Atom/RPI.Reflect/Shader/ShaderAsset.h>
#include <Atom/RPI.Reflect/Shader/ShaderCommonTypes.h>

#include <AzCore/Asset/AssetSerializer.h>
#include <AzCore/Casting/numeric_cast.h>
#include <AzCore/Serialization/SerializeContext.h>
#include <AzCore/std/algorithm.h>

#include <Atom/RHI/Factory.h>

#include <AzCore/Interface/Interface.h>
#include <Atom/RPI.Reflect/Shader/IShaderVariantFinder.h>
#include <Atom/RPI.Public/Shader/ShaderSystem.h>
#include <Atom/RPI.Public/Shader/ShaderReloadDebugTracker.h>
#include <Atom/RPI.Public/Shader/ShaderReloadNotificationBus.h>

namespace AZ
{
    namespace RPI
    {
        const ShaderVariantStableId ShaderAsset::RootShaderVariantStableId{0};

        static constexpr uint32_t SubProductTypeBitPosition = 0;
        static constexpr uint32_t SubProductTypeNumBits = SupervariantIndexBitPosition - SubProductTypeBitPosition;
        [[maybe_unused]] static constexpr uint32_t SubProductTypeMaxValue = (1 << SubProductTypeNumBits) - 1;

        static_assert(RhiIndexMaxValue == RHI::Limits::APIType::PerPlatformApiUniqueIndexMax);

        uint32_t ShaderAsset::MakeProductAssetSubId(
            uint32_t rhiApiUniqueIndex, uint32_t supervariantIndex, uint32_t subProductType)
        {
            AZ_Assert(rhiApiUniqueIndex <= RhiIndexMaxValue, "Invalid rhiApiUniqueIndex [%u]", rhiApiUniqueIndex);
            AZ_Assert(supervariantIndex <= SupervariantIndexMaxValue, "Invalid supervariantIndex [%u]", supervariantIndex);
            AZ_Assert(subProductType <= SubProductTypeMaxValue, "Invalid subProductType [%u]", subProductType);

            const uint32_t assetProductSubId = (rhiApiUniqueIndex << RhiIndexBitPosition) |
                (supervariantIndex << SupervariantIndexBitPosition) | (subProductType << SubProductTypeBitPosition);
            return assetProductSubId;
        }

        SupervariantIndex ShaderAsset::GetSupervariantIndexFromProductAssetSubId(uint32_t assetProducSubId)
        {
            const uint32_t supervariantIndex = assetProducSubId >> SupervariantIndexBitPosition;
            return SupervariantIndex{supervariantIndex & SupervariantIndexMaxValue};
        }

        SupervariantIndex ShaderAsset::GetSupervariantIndexFromAssetId(const Data::AssetId& assetId)
        {
            return GetSupervariantIndexFromProductAssetSubId(assetId.m_subId);
        }

        void ShaderAsset::Supervariant::Reflect(AZ::ReflectContext* context)
        {
            if (auto* serializeContext = azrtti_cast<SerializeContext*>(context))
            {
                serializeContext->Class<Supervariant>()
                    ->Version(1)
                    ->Field("Name", &Supervariant::m_name)
                    ->Field("SrgLayoutList", &Supervariant::m_srgLayoutList)
                    ->Field("PipelineLayout", &Supervariant::m_pipelineLayoutDescriptor)
                    ->Field("InputContract", &Supervariant::m_inputContract)
                    ->Field("OutputContract", &Supervariant::m_outputContract)
                    ->Field("RenderStates", &Supervariant::m_renderStates)
                    ->Field("AttributeMapList", &Supervariant::m_attributeMaps)
                    ->Field("RootVariantAsset", &Supervariant::m_rootShaderVariantAsset)
                    ;
            }
        }

        void ShaderAsset::ShaderApiDataContainer::Reflect(AZ::ReflectContext* context)
        {
            if (auto* serializeContext = azrtti_cast<SerializeContext*>(context))
            {
                serializeContext->Class<ShaderApiDataContainer>()
                    ->Version(1)
                    ->Field("APIType", &ShaderApiDataContainer::m_APIType)
                    ->Field("Supervariants", &ShaderApiDataContainer::m_supervariants)
                    ;
            }
        }

        void ShaderAsset::Reflect(ReflectContext* context)
        {
            Supervariant::Reflect(context);

            ShaderApiDataContainer::Reflect(context);

            if (auto* serializeContext = azrtti_cast<SerializeContext*>(context))
            {
                serializeContext->Class<ShaderAsset>()
                    ->Version(1)
                    ->Field("name", &ShaderAsset::m_name)
                    ->Field("pipelineStateType", &ShaderAsset::m_pipelineStateType)
                    ->Field("shaderOptionGroupLayout", &ShaderAsset::m_shaderOptionGroupLayout)
                    ->Field("drawListName", &ShaderAsset::m_drawListName)
                    ->Field("shaderAssetBuildTimestamp", &ShaderAsset::m_shaderAssetBuildTimestamp)
                    ->Field("perAPIShaderData", &ShaderAsset::m_perAPIShaderData)
                    ;
            }
        }

        ShaderAsset::~ShaderAsset()
        {
            Data::AssetBus::Handler::BusDisconnect();
            ShaderVariantFinderNotificationBus::Handler::BusDisconnect();
            AssetInitBus::Handler::BusDisconnect();
        }

        const Name& ShaderAsset::GetName() const
        {
            return m_name;
        }

        RHI::PipelineStateType ShaderAsset::GetPipelineStateType() const
        {
            return m_pipelineStateType;
        }

        const ShaderOptionGroupLayout* ShaderAsset::GetShaderOptionGroupLayout() const
        {
            AZ_Assert(m_shaderOptionGroupLayout, "m_shaderOptionGroupLayout is null");
            return m_shaderOptionGroupLayout.get();
        }

        const Name& ShaderAsset::GetDrawListName() const
        {
            return m_drawListName;
        }

        AZStd::sys_time_t ShaderAsset::GetShaderAssetBuildTimestamp() const
        {
            return m_shaderAssetBuildTimestamp;
        }

        void ShaderAsset::SetReady()
        {
            m_status = AssetStatus::Ready;
        }


        SupervariantIndex ShaderAsset::GetSupervariantIndex(const AZ::Name& supervariantName) const
        {
            SupervariantIndex supervariantIndex = InvalidSupervariantIndex;

            // check for an RPI ShaderSystem supervariant
            RPI::ShaderSystemInterface* shaderSystemInterface = ShaderSystemInterface::Get();
            if (shaderSystemInterface && !shaderSystemInterface->GetSupervariantName().IsEmpty())
            {
                // search for the combined requested name and system supervariant name
                // Note: the shader may not support this supervariant, if it doesn't we will
                // fallback to the requested name below
                AZStd::string combinedName = supervariantName.GetCStr();
                combinedName.append(shaderSystemInterface->GetSupervariantName().GetCStr());
                supervariantIndex = GetSupervariantIndexInternal(AZ::Name(combinedName));
            }

            if (supervariantIndex == InvalidSupervariantIndex)
            {
                // search for the requested name
                supervariantIndex = GetSupervariantIndexInternal(supervariantName);
            }

            return supervariantIndex;
        }

        Data::Asset<ShaderVariantAsset> ShaderAsset::GetVariant(
            const ShaderVariantId& shaderVariantId, SupervariantIndex supervariantIndex)
        {
            auto variantFinder = AZ::Interface<IShaderVariantFinder>::Get();
            AZ_Assert(variantFinder, "The IShaderVariantFinder doesn't exist");

            Data::Asset<ShaderAsset> thisAsset(this, Data::AssetLoadBehavior::Default);
            Data::Asset<ShaderVariantAsset> shaderVariantAsset =
                variantFinder->GetShaderVariantAssetByVariantId(thisAsset, shaderVariantId, supervariantIndex);
            if (!shaderVariantAsset)
            {
                variantFinder->QueueLoadShaderVariantAssetByVariantId(thisAsset, shaderVariantId, supervariantIndex);
            }
            return shaderVariantAsset;
        }

        ShaderVariantSearchResult ShaderAsset::FindVariantStableId(const ShaderVariantId& shaderVariantId)
        {
            uint32_t dynamicOptionCount = aznumeric_cast<uint32_t>(GetShaderOptionGroupLayout()->GetShaderOptions().size());
            ShaderVariantSearchResult variantSearchResult{RootShaderVariantStableId,  dynamicOptionCount };

            if (!dynamicOptionCount)
            {
                // The shader has no options at all. There's nothing to search.
                return variantSearchResult;
            }

            auto variantFinder = AZ::Interface<IShaderVariantFinder>::Get();
            AZ_Assert(variantFinder, "The IShaderVariantFinder doesn't exist");

            {
                AZStd::shared_lock<decltype(m_variantTreeMutex)> lock(m_variantTreeMutex);
                if (m_shaderVariantTree)
                {
                    return m_shaderVariantTree->FindVariantStableId(GetShaderOptionGroupLayout(), shaderVariantId);
                }
            }

            AZStd::unique_lock<decltype(m_variantTreeMutex)> lock(m_variantTreeMutex);
            if (!m_shaderVariantTree)
            {
                m_shaderVariantTree = variantFinder->GetShaderVariantTreeAsset(GetId());
                if (!m_shaderVariantTree)
                {
                    if (!m_shaderVariantTreeLoadWasRequested)
                    {
                        variantFinder->QueueLoadShaderVariantTreeAsset(GetId());
                        m_shaderVariantTreeLoadWasRequested = true;
                    }

                    // The variant tree could be under construction or simply doesn't exist at all.
                    return variantSearchResult;
                }
            }
            return m_shaderVariantTree->FindVariantStableId(GetShaderOptionGroupLayout(), shaderVariantId);
        }

        Data::Asset<ShaderVariantAsset> ShaderAsset::GetVariant(
            ShaderVariantStableId shaderVariantStableId, SupervariantIndex supervariantIndex) const
        {
            if (!shaderVariantStableId.IsValid() || shaderVariantStableId == RootShaderVariantStableId)
            {
                return GetRootVariant(supervariantIndex);
            }

            auto variantFinder = AZ::Interface<IShaderVariantFinder>::Get();
            AZ_Assert(variantFinder, "No Variant Finder For shaderAsset with name [%s] and stableId [%u]", GetName().GetCStr(), shaderVariantStableId.GetIndex());
            Data::Asset<ShaderVariantAsset> variant =
                variantFinder->GetShaderVariantAsset(m_shaderVariantTree.GetId(), shaderVariantStableId, supervariantIndex);
            if (!variant.IsReady())
            {
                // Enqueue a request to load the variant, next time around the caller will get the asset.
                Data::AssetId variantTreeAssetId;
                {
                    AZStd::shared_lock<decltype(m_variantTreeMutex)> lock(m_variantTreeMutex);
                    if (m_shaderVariantTree)
                    {
                        variantTreeAssetId = m_shaderVariantTree.GetId();
                    }
                }
                if (variantTreeAssetId.IsValid())
                {
                    variantFinder->QueueLoadShaderVariantAsset(variantTreeAssetId, shaderVariantStableId, supervariantIndex);
                }
                return GetRootVariant(supervariantIndex);
            }
            else if (variant->GetBuildTimestamp() >= m_shaderAssetBuildTimestamp)
            {
                return variant;
            }
            else
            {
                // When rebuilding shaders we may be in a state where the ShaderAsset and root ShaderVariantAsset have been rebuilt and reloaded, but some (or all)
                // shader variants haven't been built yet. Since we want to use the latest version of the shader code, ignore the old variants and fall back to the newer root variant instead.
                return GetRootVariant(supervariantIndex);
            }
        }

        Data::Asset<ShaderVariantAsset> ShaderAsset::GetRootVariant(SupervariantIndex supervariantIndex) const
        {
            auto supervariant = GetSupervariant(supervariantIndex);
            if (!supervariant)
            {
                return Data::Asset<ShaderVariantAsset>();
            }
            return supervariant->m_rootShaderVariantAsset;
        }

        const RHI::Ptr<RHI::ShaderResourceGroupLayout>& ShaderAsset::FindShaderResourceGroupLayout(
            const Name& shaderResourceGroupName, SupervariantIndex supervariantIndex) const
        {
            auto supervariant = GetSupervariant(supervariantIndex);
            if (!supervariant)
            {
                return RHI::NullSrgLayout;
            }
            const auto& srgLayoutList = supervariant->m_srgLayoutList;
            const auto findIt = AZStd::find_if(srgLayoutList.begin(), srgLayoutList.end(), [&](const RHI::Ptr<RHI::ShaderResourceGroupLayout>& layout)
                {
                    return layout->GetName() == shaderResourceGroupName;
                });

            if (findIt != srgLayoutList.end())
            {
                return *findIt;
            }

            return RHI::NullSrgLayout;
        }

        const RHI::Ptr<RHI::ShaderResourceGroupLayout>& ShaderAsset::FindShaderResourceGroupLayout(const Name& shaderResourceGroupName) const
        {
            SupervariantIndex supervariantIndex = DefaultSupervariantIndex;

            // check for an RPI ShaderSystem specified supervariant
            // Note: we can just search for the system supervariant name, since the default supervariant is "", so no need to append
            RPI::ShaderSystemInterface* shaderSystemInterface = ShaderSystemInterface::Get();
            if (shaderSystemInterface && !shaderSystemInterface->GetSupervariantName().IsEmpty())
            {
                SupervariantIndex systemSupervariantIndex = GetSupervariantIndexInternal(shaderSystemInterface->GetSupervariantName());
                if (systemSupervariantIndex.IsValid())
                {
                    supervariantIndex = systemSupervariantIndex;
                }
            }

            return FindShaderResourceGroupLayout(shaderResourceGroupName, supervariantIndex);
        }

        const RHI::Ptr<RHI::ShaderResourceGroupLayout>& ShaderAsset::FindShaderResourceGroupLayout(
            uint32_t bindingSlot, SupervariantIndex supervariantIndex) const
        {
            auto supervariant = GetSupervariant(supervariantIndex);
            if (!supervariant)
            {
                return RHI::NullSrgLayout;
            }
            const auto& srgLayoutList = supervariant->m_srgLayoutList;
            const auto findIt =
                AZStd::find_if(srgLayoutList.begin(), srgLayoutList.end(), [&](const RHI::Ptr<RHI::ShaderResourceGroupLayout>& layout)
                {
                    return layout && layout->GetBindingSlot() == bindingSlot;
                });

            if (findIt != srgLayoutList.end())
            {
                return *findIt;
            }

            return RHI::NullSrgLayout;
        }

        const RHI::Ptr<RHI::ShaderResourceGroupLayout>& ShaderAsset::FindShaderResourceGroupLayout(uint32_t bindingSlot) const
        {
            SupervariantIndex supervariantIndex = DefaultSupervariantIndex;

            // check for an RPI ShaderSystem specified supervariant
            // Note: we can just search for the system supervariant name, since the default supervariant is "", so no need to append
            RPI::ShaderSystemInterface* shaderSystemInterface = ShaderSystemInterface::Get();
            if (shaderSystemInterface && !shaderSystemInterface->GetSupervariantName().IsEmpty())
            {
                SupervariantIndex systemSupervariantIndex = GetSupervariantIndexInternal(shaderSystemInterface->GetSupervariantName());
                if (systemSupervariantIndex.IsValid())
                {
                    supervariantIndex = systemSupervariantIndex;
                }
            }

            return FindShaderResourceGroupLayout(bindingSlot, supervariantIndex);
        }

        const RHI::Ptr<RHI::ShaderResourceGroupLayout>& ShaderAsset::FindFallbackShaderResourceGroupLayout(
            SupervariantIndex supervariantIndex) const
        {
            auto supervariant = GetSupervariant(supervariantIndex);
            if (!supervariant)
            {
                return RHI::NullSrgLayout;
            }
            const auto& srgLayoutList = supervariant->m_srgLayoutList;
            const auto findIt =
                AZStd::find_if(srgLayoutList.begin(), srgLayoutList.end(), [&](const RHI::Ptr<RHI::ShaderResourceGroupLayout>& layout)
                {
                    return layout && layout->HasShaderVariantKeyFallbackEntry();
                });

            if (findIt != srgLayoutList.end())
            {
                return *findIt;
            }

            return RHI::NullSrgLayout;
        }

        AZStd::array_view<RHI::Ptr<RHI::ShaderResourceGroupLayout>> ShaderAsset::GetShaderResourceGroupLayouts(
            SupervariantIndex supervariantIndex) const
        {
            auto supervariant = GetSupervariant(supervariantIndex);
            if (!supervariant)
            {
                return {};
            }
            return supervariant->m_srgLayoutList;
        }

        
        const RHI::Ptr<RHI::ShaderResourceGroupLayout>& ShaderAsset::GetDrawSrgLayout(SupervariantIndex supervariantIndex) const
        {
            return FindShaderResourceGroupLayout(SrgBindingSlot::Draw, supervariantIndex);
        }

        const ShaderInputContract& ShaderAsset::GetInputContract(SupervariantIndex supervariantIndex) const
        {
            auto supervariant = GetSupervariant(supervariantIndex);
            return supervariant->m_inputContract;
        }

        const ShaderOutputContract& ShaderAsset::GetOutputContract(SupervariantIndex supervariantIndex) const
        {
            auto supervariant = GetSupervariant(supervariantIndex);
            return supervariant->m_outputContract;
        }

        const RHI::RenderStates& ShaderAsset::GetRenderStates(SupervariantIndex supervariantIndex) const
        {
            auto supervariant = GetSupervariant(supervariantIndex);
            return supervariant->m_renderStates;
        }

        const RHI::PipelineLayoutDescriptor* ShaderAsset::GetPipelineLayoutDescriptor(SupervariantIndex supervariantIndex) const
        {
            auto supervariant = GetSupervariant(supervariantIndex);
            if (!supervariant)
            {
                return nullptr;
            }
            AZ_Assert(supervariant->m_pipelineLayoutDescriptor, "m_pipelineLayoutDescriptor is null");
            return supervariant->m_pipelineLayoutDescriptor.get();
        }

        AZStd::optional<RHI::ShaderStageAttributeArguments> ShaderAsset::GetAttribute(const RHI::ShaderStage& shaderStage, const Name& attributeName,
            SupervariantIndex supervariantIndex) const
        {
            auto supervariant = GetSupervariant(supervariantIndex);
            if (!supervariant)
            {
                return AZStd::nullopt;
            }
            const auto stageIndex = static_cast<uint32_t>(shaderStage);
            AZ_Assert(stageIndex < RHI::ShaderStageCount, "Invalid shader stage specified!");

            const auto& attributeMaps = supervariant->m_attributeMaps;
            const auto& attrPair = attributeMaps[stageIndex].find(attributeName);
            if (attrPair == attributeMaps[stageIndex].end())
            {
                return AZStd::nullopt;
            }

            return attrPair->second;
        }

        ShaderAsset::ShaderApiDataContainer& ShaderAsset::GetCurrentShaderApiData()
        {
            const size_t perApiShaderDataCount = m_perAPIShaderData.size();
            AZ_Assert(perApiShaderDataCount > 0, "Invalid m_perAPIShaderData");

            if (m_currentAPITypeIndex < perApiShaderDataCount)
            {
                return m_perAPIShaderData[m_currentAPITypeIndex];
            }

            // We may only endup here when running in a Builder context.
            return m_perAPIShaderData[0];
        }

        const ShaderAsset::ShaderApiDataContainer& ShaderAsset::GetCurrentShaderApiData() const
        {
            const size_t perApiShaderDataCount = m_perAPIShaderData.size();
            AZ_Assert(perApiShaderDataCount > 0, "Invalid m_perAPIShaderData");

            if (m_currentAPITypeIndex < perApiShaderDataCount)
            {
                return m_perAPIShaderData[m_currentAPITypeIndex];
            }

            // We may only endup here when running in a Builder context.
            return m_perAPIShaderData[0];
        }

        ShaderAsset::Supervariant* ShaderAsset::GetSupervariant(SupervariantIndex supervariantIndex)
        {
            auto& supervariants = GetCurrentShaderApiData().m_supervariants;
            auto index = supervariantIndex.GetIndex();
            if (index >= supervariants.size())
            {
                AZ_Error(
                    "ShaderAsset", false, "Supervariant index = %u is invalid because there are only %zu supervariants", index,
                    supervariants.size());
                return nullptr;
            }

            return &supervariants[index];
        }

        const ShaderAsset::Supervariant* ShaderAsset::GetSupervariant(SupervariantIndex supervariantIndex) const
        {
            const auto& supervariants = GetCurrentShaderApiData().m_supervariants;
            auto index = supervariantIndex.GetIndex();
            if (index >= supervariants.size())
            {
                AZ_Error(
                    "ShaderAsset", false, "Supervariant index = %u is invalid because there are only %zu supervariants", index,
                    supervariants.size());
                return nullptr;
            }

            return &supervariants[index];
        }

        SupervariantIndex ShaderAsset::GetSupervariantIndexInternal(AZ::Name supervariantName) const
        {
            const auto& supervariants = GetCurrentShaderApiData().m_supervariants;
            const uint32_t supervariantCount = static_cast<uint32_t>(supervariants.size());
            for (uint32_t index = 0; index < supervariantCount; ++index)
            {
                if (supervariants[index].m_name == supervariantName)
                {
                    return SupervariantIndex{ index };
                }
            }
            return InvalidSupervariantIndex;
        }

        bool ShaderAsset::SelectShaderApiData()
        {
            // Use the current RHI that is active to select which shader data to use.
            // We don't assert if the Factory is not available because this method could be called during build time,
            // when no Factory is available. Some assets (like the material asset) need to load the ShaderAsset 
            // in order to get some non API specific data (like a ShaderResourceGroup) during their build
            // process. If they try to access any RHI API specific data, an assert will be trigger because the
            // correct API index will not set.
            if (RHI::Factory::IsReady())
            {
                auto rhiType = RHI::Factory::Get().GetType();
                auto findIt = AZStd::find_if(m_perAPIShaderData.begin(), m_perAPIShaderData.end(), [&rhiType](const auto& shaderData)
                    {
                        return shaderData.m_APIType == rhiType;
                    });

                if (findIt != m_perAPIShaderData.end())
                {
                    m_currentAPITypeIndex = AZStd::distance(m_perAPIShaderData.begin(), findIt);
                }
                else
                {
                    AZ_Error("ShaderAsset", false, "Could not find shader for API %s in shader %s", RHI::Factory::Get().GetName().GetCStr(), GetName().GetCStr());
                    return false;
                }
            }

            // Common finalize check
            for (const auto& shaderApiData : m_perAPIShaderData)
            {
                const auto& supervariants = shaderApiData.m_supervariants;
                for (const auto& supervariant : supervariants)
                {
                    bool beTrue = supervariant.m_attributeMaps.size() == RHI::ShaderStageCount;
                    if (!beTrue)
                    {
                        AZ_Error("ShaderAsset", false, "Unexpected number of shader stages at supervariant with name [%s]!", supervariant.m_name.GetCStr());
                        return false;
                    }
                }
            }

            return true;
        }

        bool ShaderAsset::PostLoadInit()
        {
            // Once the ShaderAsset is loaded, it is necessary to listen for changes in the Root Variant Asset.
            Data::AssetBus::Handler::BusConnect(GetRootVariant().GetId());
            ShaderVariantFinderNotificationBus::Handler::BusConnect(GetId());
                        
            AssetInitBus::Handler::BusDisconnect();

            return true;
        }
        
        void ShaderAsset::ReinitializeRootShaderVariant(Data::Asset<Data::AssetData> asset)
        {
            Data::Asset<ShaderVariantAsset> shaderVariantAsset = { asset.GetAs<ShaderVariantAsset>(), AZ::Data::AssetLoadBehavior::PreLoad };
            AZ_Assert(shaderVariantAsset->GetStableId() == RootShaderVariantStableId, "Was expecting to update the root variant");
            SupervariantIndex supervariantIndex = GetSupervariantIndexFromAssetId(asset.GetId());
            GetCurrentShaderApiData().m_supervariants[supervariantIndex.GetIndex()].m_rootShaderVariantAsset = asset;
            ShaderReloadNotificationBus::Event(GetId(), &ShaderReloadNotificationBus::Events::OnShaderAssetReinitialized, Data::Asset<ShaderAsset>{ this, AZ::Data::AssetLoadBehavior::PreLoad } );
        }

        ///////////////////////////////////////////////////////////////////////
        // AssetBus overrides...
        void ShaderAsset::OnAssetReloaded(Data::Asset<Data::AssetData> asset)
        {
            ShaderReloadDebugTracker::ScopedSection reloadSection("{%p}->ShaderAsset::OnAssetReloaded %s", this, asset.GetHint().c_str());
            ReinitializeRootShaderVariant(asset);
        }
        void ShaderAsset::OnAssetReady(Data::Asset<Data::AssetData> asset)
        {
            // We have to listen to OnAssetReady, OnAssetReloaded isn't enough, because of the following scenario:
            // The user changes a .shader file, which causes the AP to rebuild the ShaderAsset and root ShaderVariantAsset.
            // 1) Thread A creates the new ShaderAsset, loads it, and gets the old ShaderVariantAsset.
            // 2) Thread B creates the new ShaderVariantAsset, loads it, and calls OnAssetReloaded.
            // 3) Main thread calls ShaderAsset::PostLoadInit which connects to the AssetBus but it's too late to receive OnAssetReloaded, 
            //    so it continues using the old ShaderVariantAsset instead of the new one.
            // The OnAssetReady bus function is called automatically whenever a connection to AssetBus is made, so listening to this gives
            // us the opportunity to assign the appropriate ShaderVariantAsset.
            
            ShaderReloadDebugTracker::ScopedSection reloadSection("{%p}->ShaderAsset::OnAssetReady %s", this, asset.GetHint().c_str());
            ReinitializeRootShaderVariant(asset);
        }
        ///////////////////////////////////////////////////////////////////////
        
        ///////////////////////////////////////////////////////////////////
        /// ShaderVariantFinderNotificationBus overrides
        void ShaderAsset::OnShaderVariantTreeAssetReady(Data::Asset<ShaderVariantTreeAsset> shaderVariantTreeAsset, bool isError)
        {
            ShaderReloadDebugTracker::ScopedSection reloadSection("{%p}->ShaderAsset::OnShaderVariantTreeAssetReady %s", this, shaderVariantTreeAsset.GetHint().c_str());

            AZStd::unique_lock<decltype(m_variantTreeMutex)> lock(m_variantTreeMutex);
            if (isError)
            {
                m_shaderVariantTree = {}; //This will force to attempt to reload later.
                m_shaderVariantTreeLoadWasRequested = false;
            }
            else
            {
                m_shaderVariantTree = shaderVariantTreeAsset;
            }
            lock.unlock();
            ShaderReloadNotificationBus::Event(GetId(), &ShaderReloadNotificationBus::Events::OnShaderAssetReinitialized, Data::Asset<ShaderAsset>{ this, AZ::Data::AssetLoadBehavior::PreLoad });
        }

        ///////////////////////////////////////////////////////////////////


        ///////////////////////////////////////////////////////////////////////
        // ShaderAssetHandler

        Data::AssetHandler::LoadResult ShaderAssetHandler::LoadAssetData(
            const Data::Asset<Data::AssetData>& asset,
            AZStd::shared_ptr<Data::AssetDataStream> stream,
            const Data::AssetFilterCB& assetLoadFilterCB)
        {
            if (Base::LoadAssetData(asset, stream, assetLoadFilterCB) == Data::AssetHandler::LoadResult::LoadComplete)
            {
                ShaderAsset* shaderAsset = asset.GetAs<ShaderAsset>();

                // The shader API selection must occur immediately ofter loading, on the same thread, rather than
                // deferring to AssetInitBus::PostLoadInit. Many functions in the ShaderAsset class are invalid
                // until after SelectShaderApiData() is called and some client code may need to access data in
                // the ShaderAsset before then.
                if (!shaderAsset->SelectShaderApiData())
                {
                    return Data::AssetHandler::LoadResult::Error;
                }

                shaderAsset->AssetInitBus::Handler::BusConnect();

                return Data::AssetHandler::LoadResult::LoadComplete;
            }

            return Data::AssetHandler::LoadResult::Error;
        }
        
        ///////////////////////////////////////////////////////////////////////

    } // namespace RPI
} // namespace AZ