code/PostProcessing/FindDegenerates.cpp

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/** @file  FindDegenerates.cpp
 *  @brief Implementation of the FindDegenerates post-process step.
*/


// internal headers
#include "ProcessHelper.h"
#include "FindDegenerates.h"
#include <assimp/Exceptional.h>

using namespace Assimp;

//remove mesh at position 'index' from the scene
static void removeMesh(aiScene* pScene, unsigned const index);
//correct node indices to meshes and remove references to deleted mesh
static void updateSceneGraph(aiNode* pNode, unsigned const index);

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
FindDegeneratesProcess::FindDegeneratesProcess()
: mConfigRemoveDegenerates( false )
, mConfigCheckAreaOfTriangle( false ){
    // empty
}

// ------------------------------------------------------------------------------------------------
// Destructor, private as well
FindDegeneratesProcess::~FindDegeneratesProcess() {
    // nothing to do here
}

// ------------------------------------------------------------------------------------------------
// Returns whether the processing step is present in the given flag field.
bool FindDegeneratesProcess::IsActive( unsigned int pFlags) const {
    return 0 != (pFlags & aiProcess_FindDegenerates);
}

// ------------------------------------------------------------------------------------------------
// Setup import configuration
void FindDegeneratesProcess::SetupProperties(const Importer* pImp) {
    // Get the current value of AI_CONFIG_PP_FD_REMOVE
    mConfigRemoveDegenerates = (0 != pImp->GetPropertyInteger(AI_CONFIG_PP_FD_REMOVE,0));
    mConfigCheckAreaOfTriangle = ( 0 != pImp->GetPropertyInteger(AI_CONFIG_PP_FD_CHECKAREA) );
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void FindDegeneratesProcess::Execute( aiScene* pScene) {
    ASSIMP_LOG_DEBUG("FindDegeneratesProcess begin");
    for (unsigned int i = 0; i < pScene->mNumMeshes;++i)
    {
        //Do not process point cloud, ExecuteOnMesh works only with faces data
        if ((pScene->mMeshes[i]->mPrimitiveTypes != aiPrimitiveType::aiPrimitiveType_POINT) && ExecuteOnMesh(pScene->mMeshes[i])) {
            removeMesh(pScene, i);
            --i; //the current i is removed, do not skip the next one
        }
    }
    ASSIMP_LOG_DEBUG("FindDegeneratesProcess finished");
}

static void removeMesh(aiScene* pScene, unsigned const index) {
    //we start at index and copy the pointers one position forward
    //save the mesh pointer to delete it later
    auto delete_me = pScene->mMeshes[index];
    for (unsigned i = index; i < pScene->mNumMeshes - 1; ++i) {
        pScene->mMeshes[i] = pScene->mMeshes[i+1];
    }
    pScene->mMeshes[pScene->mNumMeshes - 1] = nullptr;
    --(pScene->mNumMeshes);
    delete delete_me;

    //removing a mesh also requires updating all references to it in the scene graph
    updateSceneGraph(pScene->mRootNode, index);
}

static void updateSceneGraph(aiNode* pNode, unsigned const index) {
    for (unsigned i = 0; i < pNode->mNumMeshes; ++i) {
        if (pNode->mMeshes[i] > index) {
            --(pNode->mMeshes[i]);
            continue;
        }
        if (pNode->mMeshes[i] == index) {
            for (unsigned j = i; j < pNode->mNumMeshes -1; ++j) {
                pNode->mMeshes[j] = pNode->mMeshes[j+1];
            }
            --(pNode->mNumMeshes);
            --i;
            continue;
        }
    }
    //recurse to all children
    for (unsigned i = 0; i < pNode->mNumChildren; ++i) {
        updateSceneGraph(pNode->mChildren[i], index);
    }
}

static ai_real heron( ai_real a, ai_real b, ai_real c ) {
    ai_real s = (a + b + c) / 2;
    ai_real area = pow((s * ( s - a ) * ( s - b ) * ( s - c ) ), (ai_real)0.5 );
    return area;
}

static ai_real distance3D( const aiVector3D &vA, aiVector3D &vB ) {
    const ai_real lx = ( vB.x - vA.x );
    const ai_real ly = ( vB.y - vA.y );
    const ai_real lz = ( vB.z - vA.z );
    ai_real a = lx*lx + ly*ly + lz*lz;
    ai_real d = pow( a, (ai_real)0.5 );

    return d;
}

static ai_real calculateAreaOfTriangle( const aiFace& face, aiMesh* mesh ) {
    ai_real area = 0;

    aiVector3D vA( mesh->mVertices[ face.mIndices[ 0 ] ] );
    aiVector3D vB( mesh->mVertices[ face.mIndices[ 1 ] ] );
    aiVector3D vC( mesh->mVertices[ face.mIndices[ 2 ] ] );

    ai_real a( distance3D( vA, vB ) );
    ai_real b( distance3D( vB, vC ) );
    ai_real c( distance3D( vC, vA ) );
    area = heron( a, b, c );

    return area;
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported mesh
bool FindDegeneratesProcess::ExecuteOnMesh( aiMesh* mesh) {
    mesh->mPrimitiveTypes = 0;

    std::vector<bool> remove_me;
    if (mConfigRemoveDegenerates) {
        remove_me.resize( mesh->mNumFaces, false );
    }

    unsigned int deg = 0, limit;
    for ( unsigned int a = 0; a < mesh->mNumFaces; ++a ) {
        aiFace& face = mesh->mFaces[a];
        bool first = true;

        // check whether the face contains degenerated entries
        for (unsigned int i = 0; i < face.mNumIndices; ++i) {
            // Polygons with more than 4 points are allowed to have double points, that is
            // simulating polygons with holes just with concave polygons. However,
            // double points may not come directly after another.
            limit = face.mNumIndices;
            if (face.mNumIndices > 4) {
                limit = std::min( limit, i+2 );
            }

            for (unsigned int t = i+1; t < limit; ++t) {
                if (mesh->mVertices[face.mIndices[ i ] ] == mesh->mVertices[ face.mIndices[ t ] ]) {
                    // we have found a matching vertex position
                    // remove the corresponding index from the array
                    --face.mNumIndices;
                    --limit;
                    for (unsigned int m = t; m < face.mNumIndices; ++m) {
                        face.mIndices[ m ] = face.mIndices[ m+1 ];
                    }
                    --t;

                    // NOTE: we set the removed vertex index to an unique value
                    // to make sure the developer gets notified when his
                    // application attempts to access this data.
                    face.mIndices[ face.mNumIndices ] = 0xdeadbeef;

                    if(first) {
                        ++deg;
                        first = false;
                    }

                    if ( mConfigRemoveDegenerates ) {
                        remove_me[ a ] = true;
                        goto evil_jump_outside; // hrhrhrh ... yeah, this rocks baby!
                    }
                }
            }

            if ( mConfigCheckAreaOfTriangle ) {
                if ( face.mNumIndices == 3 ) {
                    ai_real area = calculateAreaOfTriangle( face, mesh );
                    if ( area < 1e-6 ) {
                        if ( mConfigRemoveDegenerates ) {
                            remove_me[ a ] = true;
                            ++deg;
                            goto evil_jump_outside;
                        }

                        // todo: check for index which is corrupt.
                    }
                }
            }
        }

        // We need to update the primitive flags array of the mesh.
        switch (face.mNumIndices)
        {
        case 1u:
            mesh->mPrimitiveTypes |= aiPrimitiveType_POINT;
            break;
        case 2u:
            mesh->mPrimitiveTypes |= aiPrimitiveType_LINE;
            break;
        case 3u:
            mesh->mPrimitiveTypes |= aiPrimitiveType_TRIANGLE;
            break;
        default:
            mesh->mPrimitiveTypes |= aiPrimitiveType_POLYGON;
            break;
        };
evil_jump_outside:
        continue;
    }

    // If AI_CONFIG_PP_FD_REMOVE is true, remove degenerated faces from the import
    if (mConfigRemoveDegenerates && deg) {
        unsigned int n = 0;
        for (unsigned int a = 0; a < mesh->mNumFaces; ++a)
        {
            aiFace& face_src = mesh->mFaces[a];
            if (!remove_me[a]) {
                aiFace& face_dest = mesh->mFaces[n++];

                // Do a manual copy, keep the index array
                face_dest.mNumIndices = face_src.mNumIndices;
                face_dest.mIndices    = face_src.mIndices;

                if (&face_src != &face_dest) {
                    // clear source
                    face_src.mNumIndices = 0;
                    face_src.mIndices = nullptr;
                }
            }
            else {
                // Otherwise delete it if we don't need this face
                delete[] face_src.mIndices;
                face_src.mIndices = nullptr;
                face_src.mNumIndices = 0;
            }
        }
        // Just leave the rest of the array unreferenced, we don't care for now
        mesh->mNumFaces = n;
        if (!mesh->mNumFaces) {
            //The whole mesh consists of degenerated faces
            //signal upward, that this mesh should be deleted.
            ASSIMP_LOG_DEBUG("FindDegeneratesProcess removed a mesh full of degenerated primitives");
            return true;
        }
    }

    if (deg && !DefaultLogger::isNullLogger()) {
        ASSIMP_LOG_WARN_F( "Found ", deg, " degenerated primitives");
    }
    return false;
}