o3de/Gems/SceneProcessing/Code/Source/Generation/Components/MeshOptimizer/MeshBuilderSkinningInfo.h

/*
 * 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
 *
 */

#pragma once

#include <AzCore/Memory/Memory.h>
#include <AzCore/base.h>
#include <AzCore/std/containers/vector.h>
#include "MeshBuilderInvalidIndex.h"

namespace AZ::MeshBuilder
{
    class MeshBuilderSkinningInfo
    {
    public:

        AZ_CLASS_ALLOCATOR_DECL

        struct Influence
        {
            size_t  mNodeNr = InvalidIndex;
            float   mWeight = 1.0f;

            Influence() = default;
            Influence(size_t nodeNr, float weight)
                : mNodeNr(nodeNr)
                , mWeight(weight)
            {}
        };

        MeshBuilderSkinningInfo(size_t numOrgVertices);

        void AddInfluence(size_t orgVtxNr, const Influence& influence)             { mInfluences.resize(AZStd::max(mInfluences.size(), orgVtxNr + 1)); mInfluences.at(orgVtxNr).emplace_back(influence); }
        void RemoveInfluence(size_t orgVtxNr, size_t influenceNr)                  { mInfluences.at(orgVtxNr).erase(mInfluences.at(orgVtxNr).begin() + influenceNr); }
        const Influence& GetInfluence(size_t orgVtxNr, size_t influenceNr) const   { return mInfluences.at(orgVtxNr).at(influenceNr); }
        size_t GetNumInfluences(size_t orgVtxNr) const                             { return mInfluences.at(orgVtxNr).size(); }
        size_t GetNumOrgVertices() const                                           { return mInfluences.size(); }
        void OptimizeMemoryUsage()
        {
            for (auto& subArray : mInfluences)
            {
                subArray.shrink_to_fit();
            }
            mInfluences.shrink_to_fit();
        }

        // optimize the weight data
        void Optimize(AZStd::vector<Influence>& influences, AZ::u32 maxNumWeightsPerVertex = 4, float weightThreshold = 0.0001f);

        // optimize weights
        static void OptimizeSkinningInfluences(AZStd::vector<Influence>& influences, float tolerance, size_t maxWeights);

        // sort the influences, starting with the biggest weight
        static void SortInfluencesByWeight(AZStd::vector<Influence>& influences);

    private:
        AZStd::vector<AZStd::vector<Influence>> mInfluences;
    };
} // namespace AZ::MeshBuilder