NormalsComputerClass/NormalsComputerClass.cpp at master · Smorodov/NormalsComputerClass · GitHub

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#include <set>
#include <vector>

//---------------------------------------------------------------------------
// Simple class for triangle mesh normals computarion
//---------------------------------------------------------------------------
class NormalsComputer
{
private:
    // vector of vertices shared triangles
    // vertex normals compured by averaging face normals
    std::vector < std::set<unsigned int> > sharedTriangles;
    std::vector<unsigned int> faces;
public:
    //-------------------
    // constructor
    //-------------------
    NormalsComputer(std::vector<unsigned int>& faces)
    {
        this->faces.assign(faces.begin(), faces.end());
        // need to compute once per mesh
        computeSharedTriangles(faces, sharedTriangles);
    }
    //-------------------
    // destructor
    //-------------------
    ~NormalsComputer()
    {

    }
    //--------------------------------------------------------------------------
    // compute vertex normals
    // input: vertices as array of floats in v1x,v1y,v1z,...vmx,vmy,vmz format
    //--------------------------------------------------------------------------
    void getVertexNormals(unsigned int nVertices, float* vertices, float* verticesNormals)
    {
        computeVertexNormals(faces.size(), nVertices, faces.data(), vertices, verticesNormals);
    }
    //--------------------------------------------------------------------------
    // same for std::vector type
    //--------------------------------------------------------------------------
    void getVertexNormals(std::vector<float>& vertices, std::vector<float>& verticesNormals)
    {
        computeVertexNormals(faces, vertices, verticesNormals);
    }
    //--------------------------------------------------------------------------
    // same for face normals
    //--------------------------------------------------------------------------
    void getFaceNormals(std::vector<float>& vertices, std::vector<float>& normals)
    {
        computeFaceNormals(faces, vertices, normals);
    }
private:
    //--------------------------------------------------------------------------
    // compute trianges shared by each vertex
    //--------------------------------------------------------------------------
    void computeSharedTriangles(std::vector<unsigned int>& faces, std::vector < std::set<unsigned int> >& result)
    {
        unsigned int max_ind = *std::max_element(faces.begin(), faces.end()) + 1;
        result.resize(max_ind);

        for (unsigned int i = 0; i < faces.size() / 3; ++i)
        {
            unsigned int a = faces.data()[i * 3 + 0];
            unsigned int b = faces.data()[i * 3 + 1];
            unsigned int c = faces.data()[i * 3 + 2];

            if (a == b || a == c || b == c)
            {
                std::cout << "Incorrect triangle !" << std::endl;
            }
            result[a].insert(i);
            result[b].insert(i);
            result[c].insert(i);
        }
    }
    //--------------------------------------------------------------------------
    // compute one face normsl
    //--------------------------------------------------------------------------
    void computeNormal(float* a, float* b, float* c, float* normal)
    {
        float v1[3], v2[3];
        v1[0] = b[0] - a[0];
        v1[1] = b[1] - a[1];
        v1[2] = b[2] - a[2];

        v2[0] = b[0] - c[0];
        v2[1] = b[1] - c[1];
        v2[2] = b[2] - c[2];

        normal[0] = v1[1] * v2[2] - v1[2] * v2[1];
        normal[1] = v1[2] * v2[0] - v1[0] * v2[2];
        normal[2] = v1[0] * v2[1] - v1[1] * v2[0];
        float nx = normal[0];// / norm;
        float ny = normal[1];// / norm;
        float nz = normal[2];// / norm;
        float norm = sqrt(nx * nx + ny * ny + nz * nz);
        //
        normal[0] = -nx;
        normal[1] = -ny;
        normal[2] = -nz;
    }
    //--------------------------------------------------------------------------
    // compute all face normals
    //--------------------------------------------------------------------------
    void computeFaceNormals(std::vector<unsigned int>& faces, std::vector<float>& vertices, std::vector<float>& normals)
    {
        normals.clear();
        normals.resize(faces.size(), 0);
        float* a;
        float* b;
        float* c;
        float* N;

        for (unsigned int i = 0; i < faces.size() / 3; ++i)
        {
            unsigned int a_ind = faces[3 * i + 0];
            unsigned int b_ind = faces[3 * i + 1];
            unsigned int c_ind = faces[3 * i + 2];
            if (a_ind == b_ind || a_ind == c_ind || b_ind == c_ind)
            {
                std::cout << "Incorrect triangle !" << std::endl;
            }
            a = vertices.data() + a_ind * 3;
            b = vertices.data() + b_ind * 3;
            c = vertices.data() + c_ind * 3;
            computeNormal(a, b, c, normals.data()+i * 3);
        }
    }
    //--------------------------------------------------------------------------
    // compute vertex normals by averaging shared face normals
    //--------------------------------------------------------------------------
    void computeVertexNormals(std::vector<unsigned int>& faces, std::vector<float>& vertices, std::vector<float>& result)
    {
        result.resize(vertices.size());
        std::fill(result.begin(), result.end(), 0);
        std::vector<float> faceNormals;
        computeFaceNormals(faces, vertices, faceNormals);
        for (unsigned int i = 0; i < sharedTriangles.size(); ++i)
        {
            std::set<unsigned int>::iterator it;
            for (it = sharedTriangles[i].begin(); it != sharedTriangles[i].end(); ++it)
            {
                unsigned int t = *it;
                result[i * 3 + 0] += faceNormals[t * 3 + 0];
                result[i * 3 + 1] += faceNormals[t * 3 + 1];
                result[i * 3 + 2] += faceNormals[t * 3 + 2];
            }
            float n = sqrt(result[i * 3 + 0] * result[i * 3 + 0] + result[i * 3 + 1] * result[i * 3 + 1] + result[i * 3 + 2] * result[i * 3 + 2]);
            if (n > 0)
            {
                result[i * 3 + 0] /= n;
                result[i * 3 + 1] /= n;
                result[i * 3 + 2] /= n;
            }
            else
            {
                std::cout << "zero normal" << std::endl;
            }
        }
    }
    //--------------------------------------------------------------------------
    // smae as before for pointers
    //--------------------------------------------------------------------------
    void computeVertexNormals(unsigned int nFaces, unsigned int nVertices, unsigned int* faces, float* vertices, float* result)
    {
        std::vector<unsigned int> vfaces(nFaces);
        std::vector<float> vvertices(nVertices);
        memcpy(vfaces.data(), faces, nFaces*sizeof(unsigned int));
        memcpy(vvertices.data(), vertices, nVertices * sizeof(float));
        std::vector<float> vresult;
        computeVertexNormals(vfaces, vvertices, vresult);
        memcpy(result, vresult.data(), vresult.size() * sizeof(float));
    }
};