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/** @file  FindInstancesProcess.cpp
 *  @brief Implementation of the aiProcess_FindInstances postprocessing step
*/


#include "FindInstancesProcess.h"
#include <memory>
#include <stdio.h>

using namespace Assimp;

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
FindInstancesProcess::FindInstancesProcess()
:   configSpeedFlag (false)
{}

// ------------------------------------------------------------------------------------------------
// Destructor, private as well
FindInstancesProcess::~FindInstancesProcess() = default;

// ------------------------------------------------------------------------------------------------
// Returns whether the processing step is present in the given flag field.
bool FindInstancesProcess::IsActive( unsigned int pFlags) const
{
    // FindInstances makes absolutely no sense together with PreTransformVertices
    // fixme: spawn error message somewhere else?
    return 0 != (pFlags & aiProcess_FindInstances) && 0 == (pFlags & aiProcess_PreTransformVertices);
}

// ------------------------------------------------------------------------------------------------
// Setup properties for the step
void FindInstancesProcess::SetupProperties(const Importer* pImp)
{
    // AI_CONFIG_FAVOUR_SPEED
    configSpeedFlag = (0 != pImp->GetPropertyInteger(AI_CONFIG_FAVOUR_SPEED,0));
}

// ------------------------------------------------------------------------------------------------
// Compare the bones of two meshes
bool CompareBones(const aiMesh* orig, const aiMesh* inst)
{
    for (unsigned int i = 0; i < orig->mNumBones;++i) {
        aiBone* aha = orig->mBones[i];
        aiBone* oha = inst->mBones[i];

        if (aha->mNumWeights   != oha->mNumWeights   ||
            aha->mOffsetMatrix != oha->mOffsetMatrix) {
            return false;
        }

        // compare weight per weight ---
        for (unsigned int n = 0; n < aha->mNumWeights;++n) {
            if  (aha->mWeights[n].mVertexId != oha->mWeights[n].mVertexId ||
                (aha->mWeights[n].mWeight - oha->mWeights[n].mWeight) < 10e-3f) {
                return false;
            }
        }
    }
    return true;
}

// ------------------------------------------------------------------------------------------------
// Update mesh indices in the node graph
void UpdateMeshIndices(aiNode* node, unsigned int* lookup)
{
    for (unsigned int n = 0; n < node->mNumMeshes;++n)
        node->mMeshes[n] = lookup[node->mMeshes[n]];

    for (unsigned int n = 0; n < node->mNumChildren;++n)
        UpdateMeshIndices(node->mChildren[n],lookup);
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void FindInstancesProcess::Execute( aiScene* pScene)
{
    ASSIMP_LOG_DEBUG("FindInstancesProcess begin");
    if (pScene->mNumMeshes) {

        // use a pseudo hash for all meshes in the scene to quickly find
        // the ones which are possibly equal. This step is executed early
        // in the pipeline, so we could, depending on the file format,
        // have several thousand small meshes. That's too much for a brute
        // everyone-against-everyone check involving up to 10 comparisons
        // each.
        std::unique_ptr<uint64_t[]> hashes (new uint64_t[pScene->mNumMeshes]);
        std::unique_ptr<unsigned int[]> remapping (new unsigned int[pScene->mNumMeshes]);

        unsigned int numMeshesOut = 0;
        for (unsigned int i = 0; i < pScene->mNumMeshes; ++i) {

            aiMesh* inst = pScene->mMeshes[i];
            hashes[i] = GetMeshHash(inst);

            // Find an appropriate epsilon
            // to compare position differences against
            float epsilon = ComputePositionEpsilon(inst);
            epsilon *= epsilon;

            for (int a = i-1; a >= 0; --a) {
                if (hashes[i] == hashes[a])
                {
                    aiMesh* orig = pScene->mMeshes[a];
                    if (!orig)
                        continue;

                    // check for hash collision .. we needn't check
                    // the vertex format, it *must* match due to the
                    // (brilliant) construction of the hash
                    if (orig->mNumBones       != inst->mNumBones      ||
                        orig->mNumFaces       != inst->mNumFaces      ||
                        orig->mNumVertices    != inst->mNumVertices   ||
                        orig->mMaterialIndex  != inst->mMaterialIndex ||
                        orig->mPrimitiveTypes != inst->mPrimitiveTypes)
                        continue;

                    // up to now the meshes are equal. Now compare vertex positions, normals,
                    // tangents and bitangents using this epsilon.
                    if (orig->HasPositions()) {
                        if(!CompareArrays(orig->mVertices,inst->mVertices,orig->mNumVertices,epsilon))
                            continue;
                    }
                    if (orig->HasNormals()) {
                        if(!CompareArrays(orig->mNormals,inst->mNormals,orig->mNumVertices,epsilon))
                            continue;
                    }
                    if (orig->HasTangentsAndBitangents()) {
                        if (!CompareArrays(orig->mTangents,inst->mTangents,orig->mNumVertices,epsilon) ||
                            !CompareArrays(orig->mBitangents,inst->mBitangents,orig->mNumVertices,epsilon))
                            continue;
                    }

                    // use a constant epsilon for colors and UV coordinates
                    static const float uvEpsilon = 10e-4f;
                    {
                        unsigned int j, end = orig->GetNumUVChannels();
                        for(j = 0; j < end; ++j) {
                            if (!orig->mTextureCoords[j]) {
                                continue;
                            }
                            if(!CompareArrays(orig->mTextureCoords[j],inst->mTextureCoords[j],orig->mNumVertices,uvEpsilon)) {
                                break;
                            }
                        }
                        if (j != end) {
                            continue;
                        }
                    }
                    {
                        unsigned int j, end = orig->GetNumColorChannels();
                        for(j = 0; j < end; ++j) {
                            if (!orig->mColors[j]) {
                                continue;
                            }
                            if(!CompareArrays(orig->mColors[j],inst->mColors[j],orig->mNumVertices,uvEpsilon)) {
                                break;
                            }
                        }
                        if (j != end) {
                            continue;
                        }
                    }

                    // These two checks are actually quite expensive and almost *never* required.
                    // Almost. That's why they're still here. But there's no reason to do them
                    // in speed-targeted imports.
                    if (!configSpeedFlag) {

                        // It seems to be strange, but we really need to check whether the
                        // bones are identical too. Although it's extremely unprobable
                        // that they're not if control reaches here, we need to deal
                        // with unprobable cases, too. It could still be that there are
                        // equal shapes which are deformed differently.
                        if (!CompareBones(orig,inst))
                            continue;

                        // For completeness ... compare even the index buffers for equality
                        // face order & winding order doesn't care. Input data is in verbose format.
                        std::unique_ptr<unsigned int[]> ftbl_orig(new unsigned int[orig->mNumVertices]);
                        std::unique_ptr<unsigned int[]> ftbl_inst(new unsigned int[orig->mNumVertices]);

                        for (unsigned int tt = 0; tt < orig->mNumFaces;++tt) {
                            aiFace& f = orig->mFaces[tt];
                            for (unsigned int nn = 0; nn < f.mNumIndices;++nn)
                                ftbl_orig[f.mIndices[nn]] = tt;

                            aiFace& f2 = inst->mFaces[tt];
                            for (unsigned int nn = 0; nn < f2.mNumIndices;++nn)
                                ftbl_inst[f2.mIndices[nn]] = tt;
                        }
                        if (0 != ::memcmp(ftbl_inst.get(),ftbl_orig.get(),orig->mNumVertices*sizeof(unsigned int)))
                            continue;
                    }

                    // We're still here. Or in other words: 'inst' is an instance of 'orig'.
                    // Place a marker in our list that we can easily update mesh indices.
                    remapping[i] = remapping[a];

                    // Delete the instanced mesh, we don't need it anymore
                    delete inst;
                    pScene->mMeshes[i] = nullptr;
                    break;
                }
            }

            // If we didn't find a match for the current mesh: keep it
            if (pScene->mMeshes[i]) {
                remapping[i] = numMeshesOut++;
            }
        }
        ai_assert(0 != numMeshesOut);
        if (numMeshesOut != pScene->mNumMeshes) {

            // Collapse the meshes array by removing all nullptr entries
            for (unsigned int real = 0, i = 0; real < numMeshesOut; ++i) {
                if (pScene->mMeshes[i])
                    pScene->mMeshes[real++] = pScene->mMeshes[i];
            }

            // And update the node graph with our nice lookup table
            UpdateMeshIndices(pScene->mRootNode,remapping.get());

            // write to log
            if (!DefaultLogger::isNullLogger()) {
                ASSIMP_LOG_INFO( "FindInstancesProcess finished. Found ", (pScene->mNumMeshes - numMeshesOut), " instances" );
            }
            pScene->mNumMeshes = numMeshesOut;
        } else {
            ASSIMP_LOG_DEBUG("FindInstancesProcess finished. No instanced meshes found");
        }
    }
}
