assimp/code/Common/SceneCombiner.cpp

/*
Open Asset Import Library (assimp)
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*/

// TODO: refactor entire file to get rid of the "flat-copy" first approach
// to copying structures. This easily breaks in the most unintuitive way
// possible as new fields are added to assimp structures.

// ----------------------------------------------------------------------------
/**
  * @file Implements Assimp::SceneCombiner. This is a smart utility
  *       class that combines multiple scenes, meshes, ... into one. Currently
  *       these utilities are used by the IRR and LWS loaders and the
  *       OptimizeGraph step.
  */
// ----------------------------------------------------------------------------
#include "ScenePrivate.h"
#include "time.h"
#include <assimp/Hash.h>
#include <assimp/SceneCombiner.h>
#include <assimp/StringUtils.h>
#include <assimp/fast_atof.h>
#include <assimp/mesh.h>
#include <assimp/metadata.h>
#include <assimp/scene.h>
#include <stdio.h>
#include <assimp/DefaultLogger.hpp>

namespace Assimp {

#if (__GNUC__ >= 8 && __GNUC_MINOR__ >= 0)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wclass-memaccess"
#endif

// ------------------------------------------------------------------------------------------------
// Add a prefix to a string
inline void PrefixString(aiString &string, const char *prefix, unsigned int len) {
    // If the string is already prefixed, we won't prefix it a second time
    if (string.length >= 1 && string.data[0] == '$')
        return;

    if (len + string.length >= MAXLEN - 1) {
        ASSIMP_LOG_VERBOSE_DEBUG("Can't add an unique prefix because the string is too long");
        ai_assert(false);
        return;
    }

    // Add the prefix
    ::memmove(string.data + len, string.data, string.length + 1);
    ::memcpy(string.data, prefix, len);

    // And update the string's length
    string.length += len;
}

// ------------------------------------------------------------------------------------------------
// Add node identifiers to a hashing set
void SceneCombiner::AddNodeHashes(aiNode *node, std::set<unsigned int> &hashes) {
    // Add node name to hashing set if it is non-empty - empty nodes are allowed
    // and they can't have any anims assigned so its absolutely safe to duplicate them.
    if (node->mName.length) {
        hashes.insert(SuperFastHash(node->mName.data, static_cast<uint32_t>(node->mName.length)));
    }

    // Process all children recursively
    for (unsigned int i = 0; i < node->mNumChildren; ++i) {
        AddNodeHashes(node->mChildren[i], hashes);
    }
}

// ------------------------------------------------------------------------------------------------
// Add a name prefix to all nodes in a hierarchy
void SceneCombiner::AddNodePrefixes(aiNode *node, const char *prefix, unsigned int len) {
    ai_assert(nullptr != prefix);

    PrefixString(node->mName, prefix, len);

    // Process all children recursively
    for (unsigned int i = 0; i < node->mNumChildren; ++i) {
        AddNodePrefixes(node->mChildren[i], prefix, len);
    }
}

// ------------------------------------------------------------------------------------------------
// Search for matching names
bool SceneCombiner::FindNameMatch(const aiString &name, std::vector<SceneHelper> &input, unsigned int cur) {
    const unsigned int hash = SuperFastHash(name.data, static_cast<uint32_t>(name.length));

    // Check whether we find a positive match in one of the given sets
    for (unsigned int i = 0; i < input.size(); ++i) {
        if (cur != i && input[i].hashes.find(hash) != input[i].hashes.end()) {
            return true;
        }
    }
    return false;
}

// ------------------------------------------------------------------------------------------------
// Add a name prefix to all nodes in a hierarchy if a hash match is found
void SceneCombiner::AddNodePrefixesChecked(aiNode *node, const char *prefix, unsigned int len,
        std::vector<SceneHelper> &input, unsigned int cur) {
    ai_assert(nullptr != prefix);

    const unsigned int hash = SuperFastHash(node->mName.data, static_cast<uint32_t>(node->mName.length));

    // Check whether we find a positive match in one of the given sets
    for (unsigned int i = 0; i < input.size(); ++i) {
        if (cur != i && input[i].hashes.find(hash) != input[i].hashes.end()) {
            PrefixString(node->mName, prefix, len);
            break;
        }
    }

    // Process all children recursively
    for (unsigned int i = 0; i < node->mNumChildren; ++i) {
        AddNodePrefixesChecked(node->mChildren[i], prefix, len, input, cur);
    }
}

// ------------------------------------------------------------------------------------------------
// Add an offset to all mesh indices in a node graph
void SceneCombiner::OffsetNodeMeshIndices(aiNode *node, unsigned int offset) {
    for (unsigned int i = 0; i < node->mNumMeshes; ++i)
        node->mMeshes[i] += offset;

    for (unsigned int i = 0; i < node->mNumChildren; ++i) {
        OffsetNodeMeshIndices(node->mChildren[i], offset);
    }
}

// ------------------------------------------------------------------------------------------------
// Merges two scenes. Currently only used by the LWS loader.
void SceneCombiner::MergeScenes(aiScene **_dest, std::vector<aiScene *> &src, unsigned int flags) {
    if (nullptr == _dest) {
        return;
    }

    // if _dest points to nullptr allocate a new scene. Otherwise clear the old and reuse it
    if (src.empty()) {
        if (*_dest) {
            (*_dest)->~aiScene();
            SceneCombiner::CopySceneFlat(_dest, src[0]);
        } else
            *_dest = src[0];
        return;
    }
    if (*_dest) {
        (*_dest)->~aiScene();
        new (*_dest) aiScene();
    } else
        *_dest = new aiScene();

    // Create a dummy scene to serve as master for the others
    aiScene *master = new aiScene();
    master->mRootNode = new aiNode();
    master->mRootNode->mName.Set("<MergeRoot>");

    std::vector<AttachmentInfo> srcList(src.size());
    for (unsigned int i = 0; i < srcList.size(); ++i) {
        srcList[i] = AttachmentInfo(src[i], master->mRootNode);
    }

    // 'master' will be deleted afterwards
    MergeScenes(_dest, master, srcList, flags);
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::AttachToGraph(aiNode *attach, std::vector<NodeAttachmentInfo> &srcList) {
    unsigned int cnt;
    for (cnt = 0; cnt < attach->mNumChildren; ++cnt) {
        AttachToGraph(attach->mChildren[cnt], srcList);
    }

    cnt = 0;
    for (std::vector<NodeAttachmentInfo>::iterator it = srcList.begin();
            it != srcList.end(); ++it) {
        if ((*it).attachToNode == attach && !(*it).resolved)
            ++cnt;
    }

    if (cnt) {
        aiNode **n = new aiNode *[cnt + attach->mNumChildren];
        if (attach->mNumChildren) {
            ::memcpy(n, attach->mChildren, sizeof(void *) * attach->mNumChildren);
            delete[] attach->mChildren;
        }
        attach->mChildren = n;

        n += attach->mNumChildren;
        attach->mNumChildren += cnt;

        for (unsigned int i = 0; i < srcList.size(); ++i) {
            NodeAttachmentInfo &att = srcList[i];
            if (att.attachToNode == attach && !att.resolved) {
                *n = att.node;
                (**n).mParent = attach;
                ++n;

                // mark this attachment as resolved
                att.resolved = true;
            }
        }
    }
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::AttachToGraph(aiScene *master, std::vector<NodeAttachmentInfo> &src) {
    ai_assert(nullptr != master);

    AttachToGraph(master->mRootNode, src);
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::MergeScenes(aiScene **_dest, aiScene *master, std::vector<AttachmentInfo> &srcList, unsigned int flags) {
    if (nullptr == _dest) {
        return;
    }

    // if _dest points to nullptr allocate a new scene. Otherwise clear the old and reuse it
    if (srcList.empty()) {
        if (*_dest) {
            SceneCombiner::CopySceneFlat(_dest, master);
        } else
            *_dest = master;
        return;
    }
    if (*_dest) {
        (*_dest)->~aiScene();
        new (*_dest) aiScene();
    } else
        *_dest = new aiScene();

    aiScene *dest = *_dest;

    std::vector<SceneHelper> src(srcList.size() + 1);
    src[0].scene = master;
    for (unsigned int i = 0; i < srcList.size(); ++i) {
        src[i + 1] = SceneHelper(srcList[i].scene);
    }

    // this helper array specifies which scenes are duplicates of others
    std::vector<unsigned int> duplicates(src.size(), UINT_MAX);

    // this helper array is used as lookup table several times
    std::vector<unsigned int> offset(src.size());

    // Find duplicate scenes
    for (unsigned int i = 0; i < src.size(); ++i) {
        if (duplicates[i] != i && duplicates[i] != UINT_MAX) {
            continue;
        }

        duplicates[i] = i;
        for (unsigned int a = i + 1; a < src.size(); ++a) {
            if (src[i].scene == src[a].scene) {
                duplicates[a] = i;
            }
        }
    }

    // Generate unique names for all named stuff?
    if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES) {
#if 0
        // Construct a proper random number generator
        boost::mt19937 rng(  );
        boost::uniform_int<> dist(1u,1 << 24u);
        boost::variate_generator<boost::mt19937&, boost::uniform_int<> > rndGen(rng, dist);
#endif
        for (unsigned int i = 1; i < src.size(); ++i) {
            //if (i != duplicates[i])
            //{
            //  // duplicate scenes share the same UID
            //  ::strcpy( src[i].id, src[duplicates[i]].id );
            //  src[i].idlen = src[duplicates[i]].idlen;

            //  continue;
            //}

            src[i].idlen = ai_snprintf(src[i].id, 32, "$%.6X$_", i);

            if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES_IF_NECESSARY) {

                // Compute hashes for all identifiers in this scene and store them
                // in a sorted table (for convenience I'm using std::set). We hash
                // just the node and animation channel names, all identifiers except
                // the material names should be caught by doing this.
                AddNodeHashes(src[i]->mRootNode, src[i].hashes);

                for (unsigned int a = 0; a < src[i]->mNumAnimations; ++a) {
                    aiAnimation *anim = src[i]->mAnimations[a];
                    src[i].hashes.insert(SuperFastHash(anim->mName.data, static_cast<uint32_t>(anim->mName.length)));
                }
            }
        }
    }

    unsigned int cnt;

    // First find out how large the respective output arrays must be
    for (unsigned int n = 0; n < src.size(); ++n) {
        SceneHelper *cur = &src[n];

        if (n == duplicates[n] || flags & AI_INT_MERGE_SCENE_DUPLICATES_DEEP_CPY) {
            dest->mNumTextures += (*cur)->mNumTextures;
            dest->mNumMaterials += (*cur)->mNumMaterials;
            dest->mNumMeshes += (*cur)->mNumMeshes;
        }

        dest->mNumLights += (*cur)->mNumLights;
        dest->mNumCameras += (*cur)->mNumCameras;
        dest->mNumAnimations += (*cur)->mNumAnimations;

        // Combine the flags of all scenes
        // We need to process them flag-by-flag here to get correct results
        // dest->mFlags ; //|= (*cur)->mFlags;
        if ((*cur)->mFlags & AI_SCENE_FLAGS_NON_VERBOSE_FORMAT) {
            dest->mFlags |= AI_SCENE_FLAGS_NON_VERBOSE_FORMAT;
        }
    }

    // generate the output texture list + an offset table for all texture indices
    if (dest->mNumTextures) {
        aiTexture **pip = dest->mTextures = new aiTexture *[dest->mNumTextures];
        cnt = 0;
        for (unsigned int n = 0; n < src.size(); ++n) {
            SceneHelper *cur = &src[n];
            for (unsigned int i = 0; i < (*cur)->mNumTextures; ++i) {
                if (n != duplicates[n]) {
                    if (flags & AI_INT_MERGE_SCENE_DUPLICATES_DEEP_CPY)
                        Copy(pip, (*cur)->mTextures[i]);

                    else
                        continue;
                } else
                    *pip = (*cur)->mTextures[i];
                ++pip;
            }

            offset[n] = cnt;
            cnt = (unsigned int)(pip - dest->mTextures);
        }
    }

    // generate the output material list + an offset table for all material indices
    if (dest->mNumMaterials) {
        aiMaterial **pip = dest->mMaterials = new aiMaterial *[dest->mNumMaterials];
        cnt = 0;
        for (unsigned int n = 0; n < src.size(); ++n) {
            SceneHelper *cur = &src[n];
            for (unsigned int i = 0; i < (*cur)->mNumMaterials; ++i) {
                if (n != duplicates[n]) {
                    if (flags & AI_INT_MERGE_SCENE_DUPLICATES_DEEP_CPY)
                        Copy(pip, (*cur)->mMaterials[i]);

                    else
                        continue;
                } else
                    *pip = (*cur)->mMaterials[i];

                if ((*cur)->mNumTextures != dest->mNumTextures) {
                    // We need to update all texture indices of the mesh. So we need to search for
                    // a material property called '$tex.file'

                    for (unsigned int a = 0; a < (*pip)->mNumProperties; ++a) {
                        aiMaterialProperty *prop = (*pip)->mProperties[a];
                        if (!strncmp(prop->mKey.data, "$tex.file", 9)) {
                            // Check whether this texture is an embedded texture.
                            // In this case the property looks like this: *<n>,
                            // where n is the index of the texture.
                            aiString &s = *((aiString *)prop->mData);
                            if ('*' == s.data[0]) {
                                // Offset the index and write it back ..
                                const unsigned int idx = strtoul10(&s.data[1]) + offset[n];
                                ASSIMP_itoa10(&s.data[1], sizeof(s.data) - 1, idx);
                            }
                        }

                        // Need to generate new, unique material names?
                        else if (!::strcmp(prop->mKey.data, "$mat.name") && flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_MATNAMES) {
                            aiString *pcSrc = (aiString *)prop->mData;
                            PrefixString(*pcSrc, (*cur).id, (*cur).idlen);
                        }
                    }
                }
                ++pip;
            }

            offset[n] = cnt;
            cnt = (unsigned int)(pip - dest->mMaterials);
        }
    }

    // generate the output mesh list + again an offset table for all mesh indices
    if (dest->mNumMeshes) {
        aiMesh **pip = dest->mMeshes = new aiMesh *[dest->mNumMeshes];
        cnt = 0;
        for (unsigned int n = 0; n < src.size(); ++n) {
            SceneHelper *cur = &src[n];
            for (unsigned int i = 0; i < (*cur)->mNumMeshes; ++i) {
                if (n != duplicates[n]) {
                    if (flags & AI_INT_MERGE_SCENE_DUPLICATES_DEEP_CPY)
                        Copy(pip, (*cur)->mMeshes[i]);

                    else
                        continue;
                } else
                    *pip = (*cur)->mMeshes[i];

                // update the material index of the mesh
                (*pip)->mMaterialIndex += offset[n];
                ++pip;
            }

            // reuse the offset array - store now the mesh offset in it
            offset[n] = cnt;
            cnt = (unsigned int)(pip - dest->mMeshes);
        }
    }

    std::vector<NodeAttachmentInfo> nodes;
    nodes.reserve(srcList.size());

    // ----------------------------------------------------------------------------
    // Now generate the output node graph. We need to make those
    // names in the graph that are referenced by anims or lights
    // or cameras unique. So we add a prefix to them ... $<rand>_
    // We could also use a counter, but using a random value allows us to
    // use just one prefix if we are joining multiple scene hierarchies recursively.
    // Chances are quite good we don't collide, so we try that ...
    // ----------------------------------------------------------------------------

    // Allocate space for light sources, cameras and animations
    aiLight **ppLights = dest->mLights = (dest->mNumLights ? new aiLight *[dest->mNumLights] : nullptr);

    aiCamera **ppCameras = dest->mCameras = (dest->mNumCameras ? new aiCamera *[dest->mNumCameras] : nullptr);

    aiAnimation **ppAnims = dest->mAnimations = (dest->mNumAnimations ? new aiAnimation *[dest->mNumAnimations] : nullptr);

    for (int n = static_cast<int>(src.size() - 1); n >= 0; --n) /* !!! important !!! */
    {
        SceneHelper *cur = &src[n];
        aiNode *node;

        // To offset or not to offset, this is the question
        if (n != (int)duplicates[n]) {
            // Get full scene-graph copy
            Copy(&node, (*cur)->mRootNode);
            OffsetNodeMeshIndices(node, offset[duplicates[n]]);

            if (flags & AI_INT_MERGE_SCENE_DUPLICATES_DEEP_CPY) {
                // (note:) they are already 'offseted' by offset[duplicates[n]]
                OffsetNodeMeshIndices(node, offset[n] - offset[duplicates[n]]);
            }
        } else // if (n == duplicates[n])
        {
            node = (*cur)->mRootNode;
            OffsetNodeMeshIndices(node, offset[n]);
        }
        if (n) // src[0] is the master node
            nodes.push_back(NodeAttachmentInfo(node, srcList[n - 1].attachToNode, n));

        // add name prefixes?
        if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES) {

            // or the whole scenegraph
            if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES_IF_NECESSARY) {
                AddNodePrefixesChecked(node, (*cur).id, (*cur).idlen, src, n);
            } else
                AddNodePrefixes(node, (*cur).id, (*cur).idlen);

            // meshes
            for (unsigned int i = 0; i < (*cur)->mNumMeshes; ++i) {
                aiMesh *mesh = (*cur)->mMeshes[i];

                // rename all bones
                for (unsigned int a = 0; a < mesh->mNumBones; ++a) {
                    if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES_IF_NECESSARY) {
                        if (!FindNameMatch(mesh->mBones[a]->mName, src, n))
                            continue;
                    }
                    PrefixString(mesh->mBones[a]->mName, (*cur).id, (*cur).idlen);
                }
            }
        }

        // --------------------------------------------------------------------
        // Copy light sources
        for (unsigned int i = 0; i < (*cur)->mNumLights; ++i, ++ppLights) {
            if (n != (int)duplicates[n]) // duplicate scene?
            {
                Copy(ppLights, (*cur)->mLights[i]);
            } else
                *ppLights = (*cur)->mLights[i];

            // Add name prefixes?
            if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES) {
                if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES_IF_NECESSARY) {
                    if (!FindNameMatch((*ppLights)->mName, src, n))
                        continue;
                }

                PrefixString((*ppLights)->mName, (*cur).id, (*cur).idlen);
            }
        }

        // --------------------------------------------------------------------
        // Copy cameras
        for (unsigned int i = 0; i < (*cur)->mNumCameras; ++i, ++ppCameras) {
            if (n != (int)duplicates[n]) // duplicate scene?
            {
                Copy(ppCameras, (*cur)->mCameras[i]);
            } else
                *ppCameras = (*cur)->mCameras[i];

            // Add name prefixes?
            if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES) {
                if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES_IF_NECESSARY) {
                    if (!FindNameMatch((*ppCameras)->mName, src, n))
                        continue;
                }

                PrefixString((*ppCameras)->mName, (*cur).id, (*cur).idlen);
            }
        }

        // --------------------------------------------------------------------
        // Copy animations
        for (unsigned int i = 0; i < (*cur)->mNumAnimations; ++i, ++ppAnims) {
            if (n != (int)duplicates[n]) // duplicate scene?
            {
                Copy(ppAnims, (*cur)->mAnimations[i]);
            } else
                *ppAnims = (*cur)->mAnimations[i];

            // Add name prefixes?
            if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES) {
                if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES_IF_NECESSARY) {
                    if (!FindNameMatch((*ppAnims)->mName, src, n))
                        continue;
                }

                PrefixString((*ppAnims)->mName, (*cur).id, (*cur).idlen);

                // don't forget to update all node animation channels
                for (unsigned int a = 0; a < (*ppAnims)->mNumChannels; ++a) {
                    if (flags & AI_INT_MERGE_SCENE_GEN_UNIQUE_NAMES_IF_NECESSARY) {
                        if (!FindNameMatch((*ppAnims)->mChannels[a]->mNodeName, src, n))
                            continue;
                    }

                    PrefixString((*ppAnims)->mChannels[a]->mNodeName, (*cur).id, (*cur).idlen);
                }
            }
        }
    }

    // Now build the output graph
    AttachToGraph(master, nodes);
    dest->mRootNode = master->mRootNode;

    // Check whether we succeeded at building the output graph
    for (std::vector<NodeAttachmentInfo>::iterator it = nodes.begin();
            it != nodes.end(); ++it) {
        if (!(*it).resolved) {
            if (flags & AI_INT_MERGE_SCENE_RESOLVE_CROSS_ATTACHMENTS) {
                // search for this attachment point in all other imported scenes, too.
                for (unsigned int n = 0; n < src.size(); ++n) {
                    if (n != (*it).src_idx) {
                        AttachToGraph(src[n].scene, nodes);
                        if ((*it).resolved)
                            break;
                    }
                }
            }
            if (!(*it).resolved) {
                ASSIMP_LOG_ERROR_F("SceneCombiner: Failed to resolve attachment ", (*it).node->mName.data,
                        " ", (*it).attachToNode->mName.data);
            }
        }
    }

    // now delete all input scenes. Make sure duplicate scenes aren't
    // deleted more than one time
    for (unsigned int n = 0; n < src.size(); ++n) {
        if (n != duplicates[n]) // duplicate scene?
            continue;

        aiScene *deleteMe = src[n].scene;

        // We need to delete the arrays before the destructor is called -
        // we are reusing the array members
        delete[] deleteMe->mMeshes;
        deleteMe->mMeshes = nullptr;
        delete[] deleteMe->mCameras;
        deleteMe->mCameras = nullptr;
        delete[] deleteMe->mLights;
        deleteMe->mLights = nullptr;
        delete[] deleteMe->mMaterials;
        deleteMe->mMaterials = nullptr;
        delete[] deleteMe->mAnimations;
        deleteMe->mAnimations = nullptr;
        delete[] deleteMe->mTextures;
        deleteMe->mTextures = nullptr;

        deleteMe->mRootNode = nullptr;

        // Now we can safely delete the scene
        delete deleteMe;
    }

    // Check flags
    if (!dest->mNumMeshes || !dest->mNumMaterials) {
        dest->mFlags |= AI_SCENE_FLAGS_INCOMPLETE;
    }

    // We're finished
}

// ------------------------------------------------------------------------------------------------
// Build a list of unique bones
void SceneCombiner::BuildUniqueBoneList(std::list<BoneWithHash> &asBones,
        std::vector<aiMesh *>::const_iterator it,
        std::vector<aiMesh *>::const_iterator end) {
    unsigned int iOffset = 0;
    for (; it != end; ++it) {
        for (unsigned int l = 0; l < (*it)->mNumBones; ++l) {
            aiBone *p = (*it)->mBones[l];
            uint32_t itml = SuperFastHash(p->mName.data, (unsigned int)p->mName.length);

            std::list<BoneWithHash>::iterator it2 = asBones.begin();
            std::list<BoneWithHash>::iterator end2 = asBones.end();

            for (; it2 != end2; ++it2) {
                if ((*it2).first == itml) {
                    (*it2).pSrcBones.push_back(BoneSrcIndex(p, iOffset));
                    break;
                }
            }
            if (end2 == it2) {
                // need to begin a new bone entry
                asBones.push_back(BoneWithHash());
                BoneWithHash &btz = asBones.back();

                // setup members
                btz.first = itml;
                btz.second = &p->mName;
                btz.pSrcBones.push_back(BoneSrcIndex(p, iOffset));
            }
        }
        iOffset += (*it)->mNumVertices;
    }
}

// ------------------------------------------------------------------------------------------------
// Merge a list of bones
void SceneCombiner::MergeBones(aiMesh *out, std::vector<aiMesh *>::const_iterator it,
        std::vector<aiMesh *>::const_iterator end) {
    if (nullptr == out || out->mNumBones == 0) {
        return;
    }

    // find we need to build an unique list of all bones.
    // we work with hashes to make the comparisons MUCH faster,
    // at least if we have many bones.
    std::list<BoneWithHash> asBones;
    BuildUniqueBoneList(asBones, it, end);

    // now create the output bones
    out->mNumBones = 0;
    out->mBones = new aiBone *[asBones.size()];

    for (std::list<BoneWithHash>::const_iterator boneIt = asBones.begin(), boneEnd = asBones.end(); boneIt != boneEnd; ++boneIt) {
        // Allocate a bone and setup it's name
        aiBone *pc = out->mBones[out->mNumBones++] = new aiBone();
        pc->mName = aiString(*(boneIt->second));

        std::vector<BoneSrcIndex>::const_iterator wend = boneIt->pSrcBones.end();

        // Loop through all bones to be joined for this bone
        for (std::vector<BoneSrcIndex>::const_iterator wmit = boneIt->pSrcBones.begin(); wmit != wend; ++wmit) {
            pc->mNumWeights += (*wmit).first->mNumWeights;

            // NOTE: different offset matrices for bones with equal names
            // are - at the moment - not handled correctly.
            if (wmit != boneIt->pSrcBones.begin() && pc->mOffsetMatrix != wmit->first->mOffsetMatrix) {
                ASSIMP_LOG_WARN("Bones with equal names but different offset matrices can't be joined at the moment");
                continue;
            }
            pc->mOffsetMatrix = wmit->first->mOffsetMatrix;
        }

        // Allocate the vertex weight array
        aiVertexWeight *avw = pc->mWeights = new aiVertexWeight[pc->mNumWeights];

        // And copy the final weights - adjust the vertex IDs by the
        // face index offset of the corresponding mesh.
        for (std::vector<BoneSrcIndex>::const_iterator wmit = (*boneIt).pSrcBones.begin(); wmit != (*boneIt).pSrcBones.end(); ++wmit) {
            if (wmit == wend) {
                break;
            }

            aiBone *pip = (*wmit).first;
            for (unsigned int mp = 0; mp < pip->mNumWeights; ++mp, ++avw) {
                const aiVertexWeight &vfi = pip->mWeights[mp];
                avw->mWeight = vfi.mWeight;
                avw->mVertexId = vfi.mVertexId + (*wmit).second;
            }
        }
    }
}

// ------------------------------------------------------------------------------------------------
// Merge a list of meshes
void SceneCombiner::MergeMeshes(aiMesh **_out, unsigned int /*flags*/,
        std::vector<aiMesh *>::const_iterator begin,
        std::vector<aiMesh *>::const_iterator end) {
    if (nullptr == _out) {
        return;
    }

    if (begin == end) {
        *_out = nullptr; // no meshes ...
        return;
    }

    // Allocate the output mesh
    aiMesh *out = *_out = new aiMesh();
    out->mMaterialIndex = (*begin)->mMaterialIndex;

    std::string name;
    // Find out how much output storage we'll need
    for (std::vector<aiMesh *>::const_iterator it = begin; it != end; ++it) {
        const char *meshName((*it)->mName.C_Str());
        name += std::string(meshName);
        if (it != end - 1) {
            name += ".";
        }
        out->mNumVertices += (*it)->mNumVertices;
        out->mNumFaces += (*it)->mNumFaces;
        out->mNumBones += (*it)->mNumBones;

        // combine primitive type flags
        out->mPrimitiveTypes |= (*it)->mPrimitiveTypes;
    }
    out->mName.Set(name.c_str());

    if (out->mNumVertices) {
        aiVector3D *pv2;

        // copy vertex positions
        if ((**begin).HasPositions()) {

            pv2 = out->mVertices = new aiVector3D[out->mNumVertices];
            for (std::vector<aiMesh *>::const_iterator it = begin; it != end; ++it) {
                if ((*it)->mVertices) {
                    ::memcpy(pv2, (*it)->mVertices, (*it)->mNumVertices * sizeof(aiVector3D));
                } else
                    ASSIMP_LOG_WARN("JoinMeshes: Positions expected but input mesh contains no positions");
                pv2 += (*it)->mNumVertices;
            }
        }
        // copy normals
        if ((**begin).HasNormals()) {

            pv2 = out->mNormals = new aiVector3D[out->mNumVertices];
            for (std::vector<aiMesh *>::const_iterator it = begin; it != end; ++it) {
                if ((*it)->mNormals) {
                    ::memcpy(pv2, (*it)->mNormals, (*it)->mNumVertices * sizeof(aiVector3D));
                } else {
                    ASSIMP_LOG_WARN("JoinMeshes: Normals expected but input mesh contains no normals");
                }
                pv2 += (*it)->mNumVertices;
            }
        }
        // copy tangents and bi-tangents
        if ((**begin).HasTangentsAndBitangents()) {

            pv2 = out->mTangents = new aiVector3D[out->mNumVertices];
            aiVector3D *pv2b = out->mBitangents = new aiVector3D[out->mNumVertices];

            for (std::vector<aiMesh *>::const_iterator it = begin; it != end; ++it) {
                if ((*it)->mTangents) {
                    ::memcpy(pv2, (*it)->mTangents, (*it)->mNumVertices * sizeof(aiVector3D));
                    ::memcpy(pv2b, (*it)->mBitangents, (*it)->mNumVertices * sizeof(aiVector3D));
                } else {
                    ASSIMP_LOG_WARN("JoinMeshes: Tangents expected but input mesh contains no tangents");
                }
                pv2 += (*it)->mNumVertices;
                pv2b += (*it)->mNumVertices;
            }
        }
        // copy texture coordinates
        unsigned int n = 0;
        while ((**begin).HasTextureCoords(n)) {
            out->mNumUVComponents[n] = (*begin)->mNumUVComponents[n];

            pv2 = out->mTextureCoords[n] = new aiVector3D[out->mNumVertices];
            for (std::vector<aiMesh *>::const_iterator it = begin; it != end; ++it) {
                if ((*it)->mTextureCoords[n]) {
                    ::memcpy(pv2, (*it)->mTextureCoords[n], (*it)->mNumVertices * sizeof(aiVector3D));
                } else {
                    ASSIMP_LOG_WARN("JoinMeshes: UVs expected but input mesh contains no UVs");
                }
                pv2 += (*it)->mNumVertices;
            }
            ++n;
        }
        // copy vertex colors
        n = 0;
        while ((**begin).HasVertexColors(n)) {
            aiColor4D *pVec2 = out->mColors[n] = new aiColor4D[out->mNumVertices];
            for (std::vector<aiMesh *>::const_iterator it = begin; it != end; ++it) {
                if ((*it)->mColors[n]) {
                    ::memcpy(pVec2, (*it)->mColors[n], (*it)->mNumVertices * sizeof(aiColor4D));
                } else {
                    ASSIMP_LOG_WARN("JoinMeshes: VCs expected but input mesh contains no VCs");
                }
                pVec2 += (*it)->mNumVertices;
            }
            ++n;
        }
    }

    if (out->mNumFaces) // just for safety
    {
        // copy faces
        out->mFaces = new aiFace[out->mNumFaces];
        aiFace *pf2 = out->mFaces;

        unsigned int ofs = 0;
        for (std::vector<aiMesh *>::const_iterator it = begin; it != end; ++it) {
            for (unsigned int m = 0; m < (*it)->mNumFaces; ++m, ++pf2) {
                aiFace &face = (*it)->mFaces[m];
                pf2->mNumIndices = face.mNumIndices;
                pf2->mIndices = face.mIndices;

                if (ofs) {
                    // add the offset to the vertex
                    for (unsigned int q = 0; q < face.mNumIndices; ++q) {
                        face.mIndices[q] += ofs;
                    }
                }
                face.mIndices = nullptr;
            }
            ofs += (*it)->mNumVertices;
        }
    }

    // bones - as this is quite lengthy, I moved the code to a separate function
    if (out->mNumBones)
        MergeBones(out, begin, end);

    // delete all source meshes
    for (std::vector<aiMesh *>::const_iterator it = begin; it != end; ++it)
        delete *it;
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::MergeMaterials(aiMaterial **dest,
        std::vector<aiMaterial *>::const_iterator begin,
        std::vector<aiMaterial *>::const_iterator end) {
    if (nullptr == dest) {
        return;
    }

    if (begin == end) {
        *dest = nullptr; // no materials ...
        return;
    }

    // Allocate the output material
    aiMaterial *out = *dest = new aiMaterial();

    // Get the maximal number of properties
    unsigned int size = 0;
    for (std::vector<aiMaterial *>::const_iterator it = begin; it != end; ++it) {
        size += (*it)->mNumProperties;
    }

    out->Clear();
    delete[] out->mProperties;

    out->mNumAllocated = size;
    out->mNumProperties = 0;
    out->mProperties = new aiMaterialProperty *[out->mNumAllocated];

    for (std::vector<aiMaterial *>::const_iterator it = begin; it != end; ++it) {
        for (unsigned int i = 0; i < (*it)->mNumProperties; ++i) {
            aiMaterialProperty *sprop = (*it)->mProperties[i];

            // Test if we already have a matching property
            const aiMaterialProperty *prop_exist;
            if (aiGetMaterialProperty(out, sprop->mKey.C_Str(), sprop->mSemantic, sprop->mIndex, &prop_exist) != AI_SUCCESS) {
                // If not, we add it to the new material
                aiMaterialProperty *prop = out->mProperties[out->mNumProperties] = new aiMaterialProperty();

                prop->mDataLength = sprop->mDataLength;
                prop->mData = new char[prop->mDataLength];
                ::memcpy(prop->mData, sprop->mData, prop->mDataLength);

                prop->mIndex = sprop->mIndex;
                prop->mSemantic = sprop->mSemantic;
                prop->mKey = sprop->mKey;
                prop->mType = sprop->mType;

                out->mNumProperties++;
            }
        }
    }
}

// ------------------------------------------------------------------------------------------------
template <typename Type>
inline void CopyPtrArray(Type **&dest, const Type *const *src, ai_uint num) {
    if (!num) {
        dest = nullptr;
        return;
    }
    dest = new Type *[num];
    for (ai_uint i = 0; i < num; ++i) {
        SceneCombiner::Copy(&dest[i], src[i]);
    }
}

// ------------------------------------------------------------------------------------------------
template <typename Type>
inline void GetArrayCopy(Type *&dest, ai_uint num) {
    if (!dest) {
        return;
    }
    Type *old = dest;

    dest = new Type[num];
    ::memcpy(dest, old, sizeof(Type) * num);
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::CopySceneFlat(aiScene **_dest, const aiScene *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    // reuse the old scene or allocate a new?
    if (*_dest) {
        (*_dest)->~aiScene();
        new (*_dest) aiScene();
    } else {
        *_dest = new aiScene();
    }
    CopyScene(_dest, src, false);
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::CopyScene(aiScene **_dest, const aiScene *src, bool allocate) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    if (allocate) {
        *_dest = new aiScene();
    }
    aiScene *dest = *_dest;
    ai_assert(nullptr != dest);

    // copy metadata
    if (nullptr != src->mMetaData) {
        dest->mMetaData = new aiMetadata(*src->mMetaData);
    }

    // copy animations
    dest->mNumAnimations = src->mNumAnimations;
    CopyPtrArray(dest->mAnimations, src->mAnimations,
            dest->mNumAnimations);

    // copy textures
    dest->mNumTextures = src->mNumTextures;
    CopyPtrArray(dest->mTextures, src->mTextures,
            dest->mNumTextures);

    // copy materials
    dest->mNumMaterials = src->mNumMaterials;
    CopyPtrArray(dest->mMaterials, src->mMaterials,
            dest->mNumMaterials);

    // copy lights
    dest->mNumLights = src->mNumLights;
    CopyPtrArray(dest->mLights, src->mLights,
            dest->mNumLights);

    // copy cameras
    dest->mNumCameras = src->mNumCameras;
    CopyPtrArray(dest->mCameras, src->mCameras,
            dest->mNumCameras);

    // copy meshes
    dest->mNumMeshes = src->mNumMeshes;
    CopyPtrArray(dest->mMeshes, src->mMeshes,
            dest->mNumMeshes);

    // now - copy the root node of the scene (deep copy, too)
    Copy(&dest->mRootNode, src->mRootNode);

    // and keep the flags ...
    dest->mFlags = src->mFlags;

    // source private data might be nullptr if the scene is user-allocated (i.e. for use with the export API)
    if (dest->mPrivate != nullptr) {
        ScenePriv(dest)->mPPStepsApplied = ScenePriv(src) ? ScenePriv(src)->mPPStepsApplied : 0;
    }
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::Copy(aiMesh **_dest, const aiMesh *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    aiMesh *dest = *_dest = new aiMesh();

    // get a flat copy
    *dest = *src;

    // and reallocate all arrays
    GetArrayCopy(dest->mVertices, dest->mNumVertices);
    GetArrayCopy(dest->mNormals, dest->mNumVertices);
    GetArrayCopy(dest->mTangents, dest->mNumVertices);
    GetArrayCopy(dest->mBitangents, dest->mNumVertices);

    unsigned int n = 0;
    while (dest->HasTextureCoords(n)) {
        GetArrayCopy(dest->mTextureCoords[n++], dest->mNumVertices);
    }

    n = 0;
    while (dest->HasVertexColors(n)) {
        GetArrayCopy(dest->mColors[n++], dest->mNumVertices);
    }

    // make a deep copy of all bones
    CopyPtrArray(dest->mBones, dest->mBones, dest->mNumBones);

    // make a deep copy of all faces
    GetArrayCopy(dest->mFaces, dest->mNumFaces);
    for (unsigned int i = 0; i < dest->mNumFaces; ++i) {
        aiFace &f = dest->mFaces[i];
        GetArrayCopy(f.mIndices, f.mNumIndices);
    }

    // make a deep copy of all blend shapes
    CopyPtrArray(dest->mAnimMeshes, dest->mAnimMeshes, dest->mNumAnimMeshes);
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::Copy(aiAnimMesh **_dest, const aiAnimMesh *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    aiAnimMesh *dest = *_dest = new aiAnimMesh();

    // get a flat copy
    *dest = *src;

    // and reallocate all arrays
    GetArrayCopy(dest->mVertices, dest->mNumVertices);
    GetArrayCopy(dest->mNormals, dest->mNumVertices);
    GetArrayCopy(dest->mTangents, dest->mNumVertices);
    GetArrayCopy(dest->mBitangents, dest->mNumVertices);

    unsigned int n = 0;
    while (dest->HasTextureCoords(n))
        GetArrayCopy(dest->mTextureCoords[n++], dest->mNumVertices);

    n = 0;
    while (dest->HasVertexColors(n))
        GetArrayCopy(dest->mColors[n++], dest->mNumVertices);
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::Copy(aiMaterial **_dest, const aiMaterial *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    aiMaterial *dest = (aiMaterial *)(*_dest = new aiMaterial());

    dest->Clear();
    delete[] dest->mProperties;

    dest->mNumAllocated = src->mNumAllocated;
    dest->mNumProperties = src->mNumProperties;
    dest->mProperties = new aiMaterialProperty *[dest->mNumAllocated];

    for (unsigned int i = 0; i < dest->mNumProperties; ++i) {
        aiMaterialProperty *prop = dest->mProperties[i] = new aiMaterialProperty();
        aiMaterialProperty *sprop = src->mProperties[i];

        prop->mDataLength = sprop->mDataLength;
        prop->mData = new char[prop->mDataLength];
        ::memcpy(prop->mData, sprop->mData, prop->mDataLength);

        prop->mIndex = sprop->mIndex;
        prop->mSemantic = sprop->mSemantic;
        prop->mKey = sprop->mKey;
        prop->mType = sprop->mType;
    }
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::Copy(aiTexture **_dest, const aiTexture *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    aiTexture *dest = *_dest = new aiTexture();

    // get a flat copy
    *dest = *src;

    // and reallocate all arrays. We must do it manually here
    const char *old = (const char *)dest->pcData;
    if (old) {
        unsigned int cpy;
        if (!dest->mHeight)
            cpy = dest->mWidth;
        else
            cpy = dest->mHeight * dest->mWidth * sizeof(aiTexel);

        if (!cpy) {
            dest->pcData = nullptr;
            return;
        }
        // the cast is legal, the aiTexel c'tor does nothing important
        dest->pcData = (aiTexel *)new char[cpy];
        ::memcpy(dest->pcData, old, cpy);
    }
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::Copy(aiAnimation **_dest, const aiAnimation *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    aiAnimation *dest = *_dest = new aiAnimation();

    // get a flat copy
    *dest = *src;

    // and reallocate all arrays
    CopyPtrArray(dest->mChannels, src->mChannels, dest->mNumChannels);
    CopyPtrArray(dest->mMorphMeshChannels, src->mMorphMeshChannels, dest->mNumMorphMeshChannels);
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::Copy(aiNodeAnim **_dest, const aiNodeAnim *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    aiNodeAnim *dest = *_dest = new aiNodeAnim();

    // get a flat copy
    *dest = *src;

    // and reallocate all arrays
    GetArrayCopy(dest->mPositionKeys, dest->mNumPositionKeys);
    GetArrayCopy(dest->mScalingKeys, dest->mNumScalingKeys);
    GetArrayCopy(dest->mRotationKeys, dest->mNumRotationKeys);
}

void SceneCombiner::Copy(aiMeshMorphAnim **_dest, const aiMeshMorphAnim *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    aiMeshMorphAnim *dest = *_dest = new aiMeshMorphAnim();

    // get a flat copy
    *dest = *src;

    // and reallocate all arrays
    GetArrayCopy(dest->mKeys, dest->mNumKeys);
    for (ai_uint i = 0; i < dest->mNumKeys; ++i) {
        dest->mKeys[i].mValues = new unsigned int[dest->mKeys[i].mNumValuesAndWeights];
        dest->mKeys[i].mWeights = new double[dest->mKeys[i].mNumValuesAndWeights];
        ::memcpy(dest->mKeys[i].mValues, src->mKeys[i].mValues, dest->mKeys[i].mNumValuesAndWeights * sizeof(unsigned int));
        ::memcpy(dest->mKeys[i].mWeights, src->mKeys[i].mWeights, dest->mKeys[i].mNumValuesAndWeights * sizeof(double));
    }
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::Copy(aiCamera **_dest, const aiCamera *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    aiCamera *dest = *_dest = new aiCamera();

    // get a flat copy, that's already OK
    *dest = *src;
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::Copy(aiLight **_dest, const aiLight *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    aiLight *dest = *_dest = new aiLight();

    // get a flat copy, that's already OK
    *dest = *src;
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::Copy(aiBone **_dest, const aiBone *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    aiBone *dest = *_dest = new aiBone();

    // get a flat copy
    *dest = *src;
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::Copy(aiNode **_dest, const aiNode *src) {
    ai_assert(nullptr != _dest);
    ai_assert(nullptr != src);

    aiNode *dest = *_dest = new aiNode();

    // get a flat copy
    *dest = *src;

    if (src->mMetaData) {
        Copy(&dest->mMetaData, src->mMetaData);
    }

    // and reallocate all arrays
    GetArrayCopy(dest->mMeshes, dest->mNumMeshes);
    CopyPtrArray(dest->mChildren, src->mChildren, dest->mNumChildren);

    // need to set the mParent fields to the created aiNode.
    for (unsigned int i = 0; i < dest->mNumChildren; i++) {
        dest->mChildren[i]->mParent = dest;
    }
}

// ------------------------------------------------------------------------------------------------
void SceneCombiner::Copy(aiMetadata **_dest, const aiMetadata *src) {
    if (nullptr == _dest || nullptr == src) {
        return;
    }

    if (0 == src->mNumProperties) {
        return;
    }

    aiMetadata *dest = *_dest = aiMetadata::Alloc(src->mNumProperties);
    std::copy(src->mKeys, src->mKeys + src->mNumProperties, dest->mKeys);

    for (unsigned int i = 0; i < src->mNumProperties; ++i) {
        aiMetadataEntry &in = src->mValues[i];
        aiMetadataEntry &out = dest->mValues[i];
        out.mType = in.mType;
        switch (dest->mValues[i].mType) {
        case AI_BOOL:
            out.mData = new bool(*static_cast<bool *>(in.mData));
            break;
        case AI_INT32:
            out.mData = new int32_t(*static_cast<int32_t *>(in.mData));
            break;
        case AI_UINT64:
            out.mData = new uint64_t(*static_cast<uint64_t *>(in.mData));
            break;
        case AI_FLOAT:
            out.mData = new float(*static_cast<float *>(in.mData));
            break;
        case AI_DOUBLE:
            out.mData = new double(*static_cast<double *>(in.mData));
            break;
        case AI_AISTRING:
            out.mData = new aiString(*static_cast<aiString *>(in.mData));
            break;
        case AI_AIVECTOR3D:
            out.mData = new aiVector3D(*static_cast<aiVector3D *>(in.mData));
            break;
        default:
            ai_assert(false);
            break;
        }
    }
}

#if (__GNUC__ >= 8 && __GNUC_MINOR__ >= 0)
#pragma GCC diagnostic pop
#endif

} // Namespace Assimp