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diff --git a/thirdparty/assimp/code/PostProcessing/RemoveRedundantMaterials.cpp b/thirdparty/assimp/code/PostProcessing/RemoveRedundantMaterials.cpp
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+/*
+---------------------------------------------------------------------------
+Open Asset Import Library (assimp)
+---------------------------------------------------------------------------
+
+Copyright (c) 2006-2019, assimp team
+
+
+
+All rights reserved.
+
+Redistribution and use of this software in source and binary forms,
+with or without modification, are permitted provided that the following
+conditions are met:
+
+* Redistributions of source code must retain the above
+  copyright notice, this list of conditions and the
+  following disclaimer.
+
+* Redistributions in binary form must reproduce the above
+  copyright notice, this list of conditions and the
+  following disclaimer in the documentation and/or other
+  materials provided with the distribution.
+
+* Neither the name of the assimp team, nor the names of its
+  contributors may be used to endorse or promote products
+  derived from this software without specific prior
+  written permission of the assimp team.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+---------------------------------------------------------------------------
+*/
+/** @file RemoveRedundantMaterials.cpp
+ *  @brief Implementation of the "RemoveRedundantMaterials" post processing step
+*/
+
+// internal headers
+
+#include "RemoveRedundantMaterials.h"
+#include <assimp/ParsingUtils.h>
+#include "ProcessHelper.h"
+#include "Material/MaterialSystem.h"
+#include <stdio.h>
+
+using namespace Assimp;
+
+// ------------------------------------------------------------------------------------------------
+// Constructor to be privately used by Importer
+RemoveRedundantMatsProcess::RemoveRedundantMatsProcess()
+: mConfigFixedMaterials() {
+    // nothing to do here
+}
+
+// ------------------------------------------------------------------------------------------------
+// Destructor, private as well
+RemoveRedundantMatsProcess::~RemoveRedundantMatsProcess()
+{
+    // nothing to do here
+}
+
+// ------------------------------------------------------------------------------------------------
+// Returns whether the processing step is present in the given flag field.
+bool RemoveRedundantMatsProcess::IsActive( unsigned int pFlags) const
+{
+    return (pFlags & aiProcess_RemoveRedundantMaterials) != 0;
+}
+
+// ------------------------------------------------------------------------------------------------
+// Setup import properties
+void RemoveRedundantMatsProcess::SetupProperties(const Importer* pImp)
+{
+    // Get value of AI_CONFIG_PP_RRM_EXCLUDE_LIST
+    mConfigFixedMaterials = pImp->GetPropertyString(AI_CONFIG_PP_RRM_EXCLUDE_LIST,"");
+}
+
+// ------------------------------------------------------------------------------------------------
+// Executes the post processing step on the given imported data.
+void RemoveRedundantMatsProcess::Execute( aiScene* pScene)
+{
+    ASSIMP_LOG_DEBUG("RemoveRedundantMatsProcess begin");
+
+    unsigned int redundantRemoved = 0, unreferencedRemoved = 0;
+    if (pScene->mNumMaterials)
+    {
+        // Find out which materials are referenced by meshes
+        std::vector<bool> abReferenced(pScene->mNumMaterials,false);
+        for (unsigned int i = 0;i < pScene->mNumMeshes;++i)
+            abReferenced[pScene->mMeshes[i]->mMaterialIndex] = true;
+
+        // If a list of materials to be excluded was given, match the list with
+        // our imported materials and 'salt' all positive matches to ensure that
+        // we get unique hashes later.
+        if (mConfigFixedMaterials.length()) {
+
+            std::list<std::string> strings;
+            ConvertListToStrings(mConfigFixedMaterials,strings);
+
+            for (unsigned int i = 0; i < pScene->mNumMaterials;++i) {
+                aiMaterial* mat = pScene->mMaterials[i];
+
+                aiString name;
+                mat->Get(AI_MATKEY_NAME,name);
+
+                if (name.length) {
+                    std::list<std::string>::const_iterator it = std::find(strings.begin(), strings.end(), name.data);
+                    if (it != strings.end()) {
+
+                        // Our brilliant 'salt': A single material property with ~ as first
+                        // character to mark it as internal and temporary.
+                        const int dummy = 1;
+                        ((aiMaterial*)mat)->AddProperty(&dummy,1,"~RRM.UniqueMaterial",0,0);
+
+                        // Keep this material even if no mesh references it
+                        abReferenced[i] = true;
+                        ASSIMP_LOG_DEBUG_F( "Found positive match in exclusion list: \'", name.data, "\'");
+                    }
+                }
+            }
+        }
+
+        // TODO: re-implement this algorithm to work in-place
+        unsigned int *aiMappingTable = new unsigned int[pScene->mNumMaterials];
+        for ( unsigned int i=0; i<pScene->mNumMaterials; i++ ) {
+            aiMappingTable[ i ] = 0;
+        }
+        unsigned int iNewNum = 0;
+
+        // Iterate through all materials and calculate a hash for them
+        // store all hashes in a list and so a quick search whether
+        // we do already have a specific hash. This allows us to
+        // determine which materials are identical.
+        uint32_t *aiHashes = new uint32_t[ pScene->mNumMaterials ];;
+        for (unsigned int i = 0; i < pScene->mNumMaterials;++i)
+        {
+            // No mesh is referencing this material, remove it.
+            if (!abReferenced[i]) {
+                ++unreferencedRemoved;
+                delete pScene->mMaterials[i];
+                pScene->mMaterials[i] = nullptr;
+                continue;
+            }
+
+            // Check all previously mapped materials for a matching hash.
+            // On a match we can delete this material and just make it ref to the same index.
+            uint32_t me = aiHashes[i] = ComputeMaterialHash(pScene->mMaterials[i]);
+            for (unsigned int a = 0; a < i;++a)
+            {
+                if (abReferenced[a] && me == aiHashes[a]) {
+                    ++redundantRemoved;
+                    me = 0;
+                    aiMappingTable[i] = aiMappingTable[a];
+                    delete pScene->mMaterials[i];
+                    pScene->mMaterials[i] = nullptr;
+                    break;
+                }
+            }
+            // This is a new material that is referenced, add to the map.
+            if (me) {
+                aiMappingTable[i] = iNewNum++;
+            }
+        }
+        // If the new material count differs from the original,
+        // we need to rebuild the material list and remap mesh material indexes.
+        if (iNewNum != pScene->mNumMaterials) {
+            ai_assert(iNewNum > 0);
+            aiMaterial** ppcMaterials = new aiMaterial*[iNewNum];
+            ::memset(ppcMaterials,0,sizeof(void*)*iNewNum);
+            for (unsigned int p = 0; p < pScene->mNumMaterials;++p)
+            {
+                // if the material is not referenced ... remove it
+                if (!abReferenced[p]) {
+                    continue;
+                }
+
+                // generate new names for modified materials that had no names
+                const unsigned int idx = aiMappingTable[p];
+                if (ppcMaterials[idx]) {
+                    aiString sz;
+                    if( ppcMaterials[idx]->Get(AI_MATKEY_NAME, sz) != AI_SUCCESS ) {
+                        sz.length = ::ai_snprintf(sz.data,MAXLEN,"JoinedMaterial_#%u",p);
+                        ((aiMaterial*)ppcMaterials[idx])->AddProperty(&sz,AI_MATKEY_NAME);
+                    }
+                } else {
+                    ppcMaterials[idx] = pScene->mMaterials[p];
+                }
+            }
+            // update all material indices
+            for (unsigned int p = 0; p < pScene->mNumMeshes;++p) {
+                aiMesh* mesh = pScene->mMeshes[p];
+                ai_assert( NULL!=mesh );
+                mesh->mMaterialIndex = aiMappingTable[mesh->mMaterialIndex];
+            }
+            // delete the old material list
+            delete[] pScene->mMaterials;
+            pScene->mMaterials = ppcMaterials;
+            pScene->mNumMaterials = iNewNum;
+        }
+        // delete temporary storage
+        delete[] aiHashes;
+        delete[] aiMappingTable;
+    }
+    if (redundantRemoved == 0 && unreferencedRemoved == 0)
+    {
+        ASSIMP_LOG_DEBUG("RemoveRedundantMatsProcess finished ");
+    }
+    else
+    {
+        ASSIMP_LOG_INFO_F("RemoveRedundantMatsProcess finished. Removed ", redundantRemoved, " redundant and ", 
+            unreferencedRemoved, " unused materials.");
+    }
+}