assimp/code/PostProcessing/FindDegenerates.cpp

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

#include "FindDegenerates.h"
#include "Geometry/GeometryUtils.h"
#include "ProcessHelper.h"

#include <assimp/Exceptional.h>

#include <unordered_map>

using namespace Assimp;

// Correct node indices to meshes and remove references to deleted mesh
static void updateSceneGraph(aiNode *pNode, const std::unordered_map<unsigned int, unsigned int> &meshMap);

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

// ------------------------------------------------------------------------------------------------
// 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");
    if (nullptr == pScene) {
        return;
    }

    std::unordered_map<unsigned int, unsigned int> meshMap;
    meshMap.reserve(pScene->mNumMeshes);

    const unsigned int originalNumMeshes = pScene->mNumMeshes;
    unsigned int targetIndex = 0;
    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])) {
            delete pScene->mMeshes[i];
            // Not strictly required, but clean:
            pScene->mMeshes[i] = nullptr;
        } else {
            meshMap[i] = targetIndex;
            pScene->mMeshes[targetIndex] = pScene->mMeshes[i];
            ++targetIndex;
        }
    }
    pScene->mNumMeshes = targetIndex;

    if (meshMap.size() < originalNumMeshes) {
        updateSceneGraph(pScene->mRootNode, meshMap);
    }

    ASSIMP_LOG_DEBUG("FindDegeneratesProcess finished");
}

static void updateSceneGraph(aiNode *pNode, const std::unordered_map<unsigned int, unsigned int> &meshMap) {
    unsigned int targetIndex = 0;
    for (unsigned i = 0; i < pNode->mNumMeshes; ++i) {
        const unsigned int sourceMeshIndex = pNode->mMeshes[i];
        auto it = meshMap.find(sourceMeshIndex);
        if (it != meshMap.end()) {
            pNode->mMeshes[targetIndex] = it->second;
            ++targetIndex;
        }
    }
    pNode->mNumMeshes = targetIndex;
    // recurse to all children
    for (unsigned i = 0; i < pNode->mNumChildren; ++i) {
        updateSceneGraph(pNode->mChildren[i], meshMap);
    }
}

// ------------------------------------------------------------------------------------------------
// 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;
        auto vertex_in_range = [numVertices = mesh->mNumVertices](unsigned int vertex_idx) { return vertex_idx < numVertices; };

        // check whether the face contains degenerated entries
        for (unsigned int i = 0; i < face.mNumIndices; ++i) {
            if (!std::all_of(face.mIndices, face.mIndices + face.mNumIndices, vertex_in_range))
                continue;

            // 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 = GeometryUtils::calculateAreaOfTriangle(face, mesh);
                    if (area < ai_epsilon) {
                        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_VERBOSE_DEBUG("FindDegeneratesProcess removed a mesh full of degenerated primitives");
            return true;
        }
    }

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