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/**

 * @file Implementation of the post-processing step to generate face

 * normals for all imported faces.

 */

#include "GenFaceNormalsProcess.h"

#include <assimp/Exceptional.h>

#include <assimp/postprocess.h>

#include <assimp/qnan.h>

#include <assimp/scene.h>

#include <assimp/DefaultLogger.hpp>

#include <numeric>

#include <memory>

using namespace Assimp;

// ------------------------------------------------------------------------------------------------

// Returns whether the processing step is in the given flag field.

bool GenFaceNormalsProcess::IsActive(unsigned int pFlags) const {

    force_ = (pFlags & aiProcess_ForceGenNormals) != 0;

    flippedWindingOrder_ = (pFlags & aiProcess_FlipWindingOrder) != 0;

    leftHanded_ = (pFlags & aiProcess_MakeLeftHanded) != 0;

    return (pFlags & aiProcess_GenNormals) != 0;

}

// ------------------------------------------------------------------------------------------------

// Executes the post-processing step on the given imported data.

void GenFaceNormalsProcess::Execute(aiScene *pScene) {

    ASSIMP_LOG_DEBUG("GenFaceNormalsProcess 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 (this->GenMeshFaceNormals(pScene->mMeshes[a])) {

            bHas = true;

        }

    }

    if (bHas) {

        ASSIMP_LOG_INFO("GenFaceNormalsProcess finished. "

                        "Face normals have been calculated");

    } else {

        ASSIMP_LOG_DEBUG("GenFaceNormalsProcess finished. "

                         "Normals are already there");

    }

}

namespace {

template<class XMesh>

void updateXMeshVertices(XMesh *pMesh, std::vector<int> &uniqueVertices) {

    // replace vertex data with the unique data sets

    pMesh->mNumVertices = static_cast<unsigned int>(uniqueVertices.size());

    // ----------------------------------------------------------------------------

    // NOTE - we're *not* calling Vertex::SortBack() because it would check for

    // presence of every single vertex component once PER VERTEX. And our CPU

    // dislikes branches, even if they're easily predictable.

    // ----------------------------------------------------------------------------

    // Position, if present (check made for aiAnimMesh)

    if (pMesh->mVertices) {

        std::unique_ptr<aiVector3D[]> oldVertices(pMesh->mVertices);

        pMesh->mVertices = new aiVector3D[pMesh->mNumVertices];

        for (unsigned int a = 0; a < pMesh->mNumVertices; a++) {

            pMesh->mVertices[a] = oldVertices[uniqueVertices[a]];

        }

    }

    // Tangents, if present

    if (pMesh->mTangents) {

        std::unique_ptr<aiVector3D[]> oldTangents(pMesh->mTangents);

        pMesh->mTangents = new aiVector3D[pMesh->mNumVertices];

        for (unsigned int a = 0; a < pMesh->mNumVertices; a++) {

            pMesh->mTangents[a] = oldTangents[uniqueVertices[a]];

        }

    }

    // Bitangents as well

    if (pMesh->mBitangents) {

        std::unique_ptr<aiVector3D[]> oldBitangents(pMesh->mBitangents);

        pMesh->mBitangents = new aiVector3D[pMesh->mNumVertices];

        for (unsigned int a = 0; a < pMesh->mNumVertices; a++) {

            pMesh->mBitangents[a] = oldBitangents[uniqueVertices[a]];

        }

    }

    // Vertex colors

    for (unsigned int a = 0; pMesh->HasVertexColors(a); a++) {

        std::unique_ptr<aiColor4D[]> oldColors(pMesh->mColors[a]);

        pMesh->mColors[a] = new aiColor4D[pMesh->mNumVertices];

        for (unsigned int b = 0; b < pMesh->mNumVertices; b++) {

            pMesh->mColors[a][b] = oldColors[uniqueVertices[b]];

        }

    }

    // Texture coords

    for (unsigned int a = 0; pMesh->HasTextureCoords(a); a++) {

        std::unique_ptr<aiVector3D[]> oldTextureCoords(pMesh->mTextureCoords[a]);

        pMesh->mTextureCoords[a] = new aiVector3D[pMesh->mNumVertices];

        for (unsigned int b = 0; b < pMesh->mNumVertices; b++) {

            pMesh->mTextureCoords[a][b] = oldTextureCoords[uniqueVertices[b]];

        }

    }

}

} // namespace

// ------------------------------------------------------------------------------------------------

// Executes the post-processing step on the given imported data.

bool GenFaceNormalsProcess::GenMeshFaceNormals(aiMesh *pMesh) {

    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 an array to hold the output normals

    std::vector<aiVector3D> normals;

    normals.resize(pMesh->mNumVertices);

    // mask to indicate if a vertex was already referenced and needs to be duplicated

    std::vector<bool> alreadyReferenced;

    alreadyReferenced.resize(pMesh->mNumVertices, false);

    std::vector<int> duplicatedVertices;

    duplicatedVertices.resize(pMesh->mNumVertices);

    std::iota(std::begin(duplicatedVertices), std::end(duplicatedVertices), 0);

    auto storeNormalSplitVertex = [&](unsigned int index, const aiVector3D& normal) {

        if (!alreadyReferenced[index]) {

            normals[index]           = normal;

            alreadyReferenced[index] = true;

        } else {

            normals.push_back(normal);

            duplicatedVertices.push_back(index);

            index = static_cast<unsigned int>(duplicatedVertices.size() - 1);

        }

        return index;

    };

    const aiVector3D undefinedNormal = aiVector3D(get_qnan());

    // iterate through all faces and 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 well-defined normal vector

            for (unsigned int i = 0; i < face.mNumIndices; ++i) {

                face.mIndices[i] = storeNormalSplitVertex(face.mIndices[i], undefinedNormal);

            }

            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]];

        // Boolean XOR - if either but not both of these flags are set, then the winding order has

        // changed and the cross-product to calculate the normal needs to be reversed

        if (flippedWindingOrder_ != leftHanded_)

            std::swap(pV2, pV3);

        const aiVector3D vNor = ((*pV2 - *pV1) ^ (*pV3 - *pV1)).NormalizeSafe();

        for (unsigned int i = 0; i < face.mNumIndices; ++i) {

            face.mIndices[i] = storeNormalSplitVertex(face.mIndices[i], vNor);

        }

    }

    // store normals (and additional vertices) back into the mesh

    if (pMesh->mNumVertices != std::size(duplicatedVertices)) {

        updateXMeshVertices(pMesh, duplicatedVertices);

    }

    pMesh->mNormals = new aiVector3D[normals.size()];

    memcpy(pMesh->mNormals, normals.data(), normals.size() * sizeof(aiVector3D));

    return true;

}