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Open Asset Import Library (assimp)
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/** @file Implementation of the post processing step to generate face
* normals for all imported faces.
*/

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

using namespace Assimp;

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
GenVertexNormalsProcess::GenVertexNormalsProcess() :
        configMaxAngle(AI_DEG_TO_RAD(175.f)) {
    // empty
}

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

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

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
void GenVertexNormalsProcess::SetupProperties(const Importer *pImp) {
    // Get the current value of the AI_CONFIG_PP_GSN_MAX_SMOOTHING_ANGLE property
    configMaxAngle = pImp->GetPropertyFloat(AI_CONFIG_PP_GSN_MAX_SMOOTHING_ANGLE, (ai_real)175.0);
    configMaxAngle = AI_DEG_TO_RAD(std::max(std::min(configMaxAngle, (ai_real)175.0), (ai_real)0.0));
}

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

    if (pScene->mFlags & AI_SCENE_FLAGS_NON_VERBOSE_FORMAT) {
        throw DeadlyImportError("Post-processing order mismatch: expecting pseudo-indexed (\"verbose\") vertices here");
    }

    bool bHas = false;
    for (unsigned int a = 0; a < pScene->mNumMeshes; ++a) {
        if (GenMeshVertexNormals(pScene->mMeshes[a], a))
            bHas = true;
    }

    if (bHas) {
        ASSIMP_LOG_INFO("GenVertexNormalsProcess finished. "
                        "Vertex normals have been calculated");
    } else {
        ASSIMP_LOG_DEBUG("GenVertexNormalsProcess finished. "
                         "Normals are already there");
    }
}

// ------------------------------------------------------------------------------------------------
// Executes the post processing step on the given imported data.
bool GenVertexNormalsProcess::GenMeshVertexNormals(aiMesh *pMesh, unsigned int meshIndex) {
    if (nullptr != pMesh->mNormals) {
        if (force_)
            delete[] pMesh->mNormals;
        else
            return false;
    }

    // If the mesh consists of lines and/or points but not of
    // triangles or higher-order polygons the normal vectors
    // are undefined.
    if (!(pMesh->mPrimitiveTypes & (aiPrimitiveType_TRIANGLE | aiPrimitiveType_POLYGON))) {
        ASSIMP_LOG_INFO("Normal vectors are undefined for line and point meshes");
        return false;
    }

    // Allocate the array to hold the output normals
    const float qnan = std::numeric_limits<ai_real>::quiet_NaN();
    pMesh->mNormals = new aiVector3D[pMesh->mNumVertices];

    // Compute per-face normals but store them per-vertex
    for (unsigned int a = 0; a < pMesh->mNumFaces; a++) {
        const aiFace &face = pMesh->mFaces[a];
        if (face.mNumIndices < 3) {
            // either a point or a line -> no normal vector
            for (unsigned int i = 0; i < face.mNumIndices; ++i) {
                pMesh->mNormals[face.mIndices[i]] = aiVector3D(qnan);
            }

            continue;
        }

        const aiVector3D *pV1 = &pMesh->mVertices[face.mIndices[0]];
        const aiVector3D *pV2 = &pMesh->mVertices[face.mIndices[1]];
        const aiVector3D *pV3 = &pMesh->mVertices[face.mIndices[face.mNumIndices - 1]];
        const aiVector3D vNor = ((*pV2 - *pV1) ^ (*pV3 - *pV1)).NormalizeSafe();

        for (unsigned int i = 0; i < face.mNumIndices; ++i) {
            pMesh->mNormals[face.mIndices[i]] = vNor;
        }
    }

    // Set up a SpatialSort to quickly find all vertices close to a given position
    // check whether we can reuse the SpatialSort of a previous step.
    SpatialSort *vertexFinder = nullptr;
    SpatialSort _vertexFinder;
    ai_real posEpsilon = ai_real(1e-5);
    if (shared) {
        std::vector<std::pair<SpatialSort, ai_real>> *avf;
        shared->GetProperty(AI_SPP_SPATIAL_SORT, avf);
        if (avf) {
            std::pair<SpatialSort, ai_real> &blubb = avf->operator[](meshIndex);
            vertexFinder = &blubb.first;
            posEpsilon = blubb.second;
        }
    }
    if (!vertexFinder) {
        _vertexFinder.Fill(pMesh->mVertices, pMesh->mNumVertices, sizeof(aiVector3D));
        vertexFinder = &_vertexFinder;
        posEpsilon = ComputePositionEpsilon(pMesh);
    }
    std::vector<unsigned int> verticesFound;
    aiVector3D *pcNew = new aiVector3D[pMesh->mNumVertices];

    if (configMaxAngle >= AI_DEG_TO_RAD(175.f)) {
        // There is no angle limit. Thus all vertices with positions close
        // to each other will receive the same vertex normal. This allows us
        // to optimize the whole algorithm a little bit ...
        std::vector<bool> abHad(pMesh->mNumVertices, false);
        for (unsigned int i = 0; i < pMesh->mNumVertices; ++i) {
            if (abHad[i]) {
                continue;
            }

            // Get all vertices that share this one ...
            vertexFinder->FindPositions(pMesh->mVertices[i], posEpsilon, verticesFound);

            aiVector3D pcNor;
            for (unsigned int a = 0; a < verticesFound.size(); ++a) {
                const aiVector3D &v = pMesh->mNormals[verticesFound[a]];
                if (is_not_qnan(v.x)) pcNor += v;
            }
            pcNor.NormalizeSafe();

            // Write the smoothed normal back to all affected normals
            for (unsigned int a = 0; a < verticesFound.size(); ++a) {
                unsigned int vidx = verticesFound[a];
                pcNew[vidx] = pcNor;
                abHad[vidx] = true;
            }
        }
    }
    // Slower code path if a smooth angle is set. There are many ways to achieve
    // the effect, this one is the most straightforward one.
    else {
        const ai_real fLimit = std::cos(configMaxAngle);
        for (unsigned int i = 0; i < pMesh->mNumVertices; ++i) {
            // Get all vertices that share this one ...
            vertexFinder->FindPositions(pMesh->mVertices[i], posEpsilon, verticesFound);

            aiVector3D vr = pMesh->mNormals[i];

            aiVector3D pcNor;
            for (unsigned int a = 0; a < verticesFound.size(); ++a) {
                aiVector3D v = pMesh->mNormals[verticesFound[a]];

                // Check whether the angle between the two normals is not too large.
                // Skip the angle check on our own normal to avoid false negatives
                // (v*v is not guaranteed to be 1.0 for all unit vectors v)
                if (is_not_qnan(v.x) && (verticesFound[a] == i || (v * vr >= fLimit)))
                    pcNor += v;
            }
            pcNew[i] = pcNor.NormalizeSafe();
        }
    }

    delete[] pMesh->mNormals;
    pMesh->mNormals = pcNew;

    return true;
}
