assimp.assimp/code/PostProcessing/TriangulateProcess.cpp

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/** @file  TriangulateProcess.cpp
 *  @brief Implementation of the post processing step to split up
 *    all faces with more than three indices into triangles.
 *
 *
 *  The triangulation algorithm will handle concave or convex polygons.
 *  Self-intersecting or non-planar polygons are not rejected, but
 *  they're probably not triangulated correctly.
 */

#ifndef ASSIMP_BUILD_NO_TRIANGULATE_PROCESS

#include "PostProcessing/TriangulateProcess.h"
#include "Common/PolyTools.h"
#include "PostProcessing/ProcessHelper.h"

#include "contrib/poly2tri/poly2tri/poly2tri.h"

#include <cstdint>
#include <memory>

namespace Assimp {

// ------------------------------------------------------------------------------------------------
// Constructor to be privately used by Importer
TriangulateProcess::TriangulateProcess() {
    // nothing to do here
}

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

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

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

    bool bHas = false;
    for (unsigned int a = 0; a < pScene->mNumMeshes; a++) {
        if (pScene->mMeshes[a]) {
            if (TriangulateMesh(pScene->mMeshes[a])) {
                bHas = true;
            }
        }
    }
    if (bHas) {
        ASSIMP_LOG_INFO("TriangulateProcess finished. All polygons have been triangulated.");
    } else {
        ASSIMP_LOG_DEBUG("TriangulateProcess finished. There was nothing to be done.");
    }
}

// ------------------------------------------------------------------------------------------------
static bool validateNumIndices(aiMesh *mesh) {
    bool bNeed = false;
    for (unsigned int a = 0; a < mesh->mNumFaces; a++) {
        const aiFace &face = mesh->mFaces[a];
        if (face.mNumIndices != 3) {
            bNeed = true;
            break;
        }
    }

    return bNeed;
}

// ------------------------------------------------------------------------------------------------
static void calulateNumOutputFaces(aiMesh *mesh, size_t &numOut, size_t &maxOut, bool &getNormals) {
    numOut = maxOut = 0;
    getNormals = true;
    for (unsigned int a = 0; a < mesh->mNumFaces; a++) {
        aiFace &face = mesh->mFaces[a];
        if (face.mNumIndices <= 4) {
            getNormals = false;
        }
        if (face.mNumIndices <= 3) {
            numOut++;

        } else {
            numOut += face.mNumIndices - 2;
            maxOut = std::max(maxOut, static_cast<size_t>(face.mNumIndices));
        }
    }
}

// ------------------------------------------------------------------------------------------------
static void quad2Triangles(const aiFace &face, const aiVector3D *verts, aiFace *curOut) {
    // quads can have at maximum one concave vertex. Determine
    // this vertex (if it exists) and start tri-fanning from
    // it.
    unsigned int start_vertex = 0;
    for (unsigned int i = 0; i < 4; ++i) {
        const aiVector3D &v0 = verts[face.mIndices[(i + 3) % 4]];
        const aiVector3D &v1 = verts[face.mIndices[(i + 2) % 4]];
        const aiVector3D &v2 = verts[face.mIndices[(i + 1) % 4]];

        const aiVector3D &v = verts[face.mIndices[i]];

        aiVector3D left = (v0 - v);
        aiVector3D diag = (v1 - v);
        aiVector3D right = (v2 - v);

        left.Normalize();
        diag.Normalize();
        right.Normalize();

        const float angle = std::acos(left * diag) + std::acos(right * diag);
        if (angle > AI_MATH_PI_F) {
            // this is the concave point
            start_vertex = i;
            break;
        }
    }

    const unsigned int temp[] = { face.mIndices[0], face.mIndices[1], face.mIndices[2], face.mIndices[3] };

    aiFace &nface = *curOut++;
    nface.mNumIndices = 3;
    nface.mIndices = face.mIndices;

    nface.mIndices[0] = temp[start_vertex];
    nface.mIndices[1] = temp[(start_vertex + 1) % 4];
    nface.mIndices[2] = temp[(start_vertex + 2) % 4];

    aiFace &sface = *curOut++;
    sface.mNumIndices = 3;
    sface.mIndices = new unsigned int[3];

    sface.mIndices[0] = temp[start_vertex];
    sface.mIndices[1] = temp[(start_vertex + 2) % 4];
    sface.mIndices[2] = temp[(start_vertex + 3) % 4];
}

// ------------------------------------------------------------------------------------------------
bool getContourFromePolyline(aiFace &face, aiMesh *pMesh, std::vector<p2t::Point *> &contour,
        aiMatrix4x4 &m, aiVector3D &vmin, aiVector3D &vmax, ai_real &zcoord) {
    aiVector3D normal;
    bool ok = true;
    m = DerivePlaneCoordinateSpace<ai_real>(pMesh->mVertices, pMesh->mNumVertices, ok, normal);
    if (!ok) {
        false;
    }
    for (unsigned int i = 0; i < face.mNumIndices; ++i) {
        unsigned int index = face.mIndices[i];

        const aiVector3D vv = m * pMesh->mVertices[index];
        // keep Z offset in the plane coordinate system. Ignoring precision issues
        // (which  are present, of course), this should be the same value for
        // all polygon vertices (assuming the polygon is planar).

        // XXX this should be guarded, but we somehow need to pick a suitable
        // epsilon
        // if(coord != -1.0f) {
        //  assert(std::fabs(coord - vv.z) < 1e-3f);
        // }
        zcoord += vv.z;
        vmin = std::min(vv, vmin);
        vmax = std::max(vv, vmax);

        contour.push_back(new p2t::Point(vv.x, vv.y));
    }

    zcoord /= pMesh->mNumVertices;

    // Further improve the projection by mapping the entire working set into
    // [0,1] range. This gives us a consistent data range so all epsilons
    // used below can be constants.
    vmax -= vmin;
    const aiVector2D one_vec(1, 1);

    for (p2t::Point* &vv : contour) {
        vv->x = (vv->x - vmin.x) / vmax.x;
        vv->y = (vv->y - vmin.y) / vmax.y;

        // sanity rounding
        aiVector2D cur_vv((ai_real) vv->x, (ai_real)vv->y);
        cur_vv = std::max(cur_vv, aiVector2D());
        cur_vv = std::min(cur_vv, one_vec);
    }

    aiMatrix4x4 mult;
    mult.a1 = static_cast<ai_real>(1.0) / vmax.x;
    mult.b2 = static_cast<ai_real>(1.0) / vmax.y;

    mult.a4 = -vmin.x * mult.a1;
    mult.b4 = -vmin.y * mult.b2;
    mult.c4 = -zcoord;
    m = mult * m;

    return true;
}

// ------------------------------------------------------------------------------------------------
// Triangulates the given mesh.
bool TriangulateProcess::TriangulateMesh(aiMesh *pMesh) {
    // Now we have aiMesh::mPrimitiveTypes, so this is only here for test cases

    if (!pMesh->mPrimitiveTypes) {
        if (!validateNumIndices(pMesh)) {
            ASSIMP_LOG_DEBUG("Error while validating number of indices.");
            return false;
        }
    } else if (!(pMesh->mPrimitiveTypes & aiPrimitiveType_POLYGON)) {
        ASSIMP_LOG_DEBUG("???!");
        return false;
    }

    // Find out how many output faces we'll get
    size_t numOut = 0, max_out = 0;
    bool getNormals = true;
    calulateNumOutputFaces(pMesh, numOut, max_out, getNormals);
    if (numOut == pMesh->mNumFaces) {
        ASSIMP_LOG_DEBUG("Error while generating contour.");
        return false;
    }

    // the output mesh will contain triangles, but no polys anymore
    pMesh->mPrimitiveTypes |= aiPrimitiveType_TRIANGLE;
    pMesh->mPrimitiveTypes &= ~aiPrimitiveType_POLYGON;

    aiFace *out = new aiFace[numOut](), *curOut = out;
    const size_t Capa = max_out + 2;
    std::vector<aiVector3D> temp_verts3d(max_out + 2); /* temporary storage for vertices */
    std::vector<aiVector2D> temp_verts(max_out + 2);

    // Apply vertex colors to represent the face winding?

    const aiVector3D *verts = pMesh->mVertices;

    // use std::unique_ptr to avoid slow std::vector<bool> specialiations
    std::unique_ptr<bool[]> done(new bool[max_out]);
    for (unsigned int a = 0; a < pMesh->mNumFaces; a++) {
        aiFace &face = pMesh->mFaces[a];

        // if it's a simple point,line or triangle: just copy it
        if (face.mNumIndices <= 3) {
            aiFace &nface = *curOut++;
            nface.mNumIndices = face.mNumIndices;
            nface.mIndices = face.mIndices;

            face.mIndices = nullptr;
        } else if (face.mNumIndices == 4) {
            // optimized code for quadrilaterals
            quad2Triangles(face, verts, curOut);
            face.mIndices = nullptr;
        } else {
            std::vector<p2t::Point *> contour;
            aiMatrix4x4 m;
            aiVector3D vmin, vmax;
            ai_real zcoord = -1;
            if (!getContourFromePolyline(face, pMesh, contour, m, vmin, vmax, zcoord)) {
                ASSIMP_LOG_DEBUG("Error while generating contour.");
                continue;
            }
            p2t::CDT cdt(contour);
            cdt.Triangulate();
            const std::vector<p2t::Triangle *> tris = cdt.GetTriangles();
            const aiMatrix4x4 matInv = m.Inverse();
            for (p2t::Triangle *tri : tris) {
                curOut->mNumIndices = 3;
                curOut->mIndices = new unsigned int[curOut->mNumIndices];
                for (int i = 0; i < 3; ++i) {
                    const aiVector2D v = aiVector2D(static_cast<ai_real>(tri->GetPoint(i)->x), static_cast<ai_real>(tri->GetPoint(i)->y));
//                    ai_assert(v.x <= 1.0 && v.x >= 0.0 && v.y <= 1.0 && v.y >= 0.0);
                    const aiVector3D v3 = matInv * aiVector3D(vmin.x + v.x * vmax.x, vmin.y + v.y * vmax.y, zcoord);
                    temp_verts3d.emplace_back(v3);
                    curOut->mIndices[i] = (unsigned int) temp_verts3d.size()-1;
                }
                curOut++;
            }
            face.mIndices = nullptr;
        }
    }

    delete[] pMesh->mFaces;
    pMesh->mFaces = out;
    pMesh->mNumVertices = (unsigned int)temp_verts3d.size();
    delete[] pMesh->mVertices;
    pMesh->mVertices = new aiVector3D[pMesh->mNumVertices];
    for (size_t i = 0; i < temp_verts3d.size(); ++i) {
        pMesh->mVertices[i] = temp_verts3d[i];
    }
    pMesh->mNumFaces = (unsigned int)(curOut - out); /* not necessarily equal to numOut */

    return true;
}

} // namespace Assimp

#endif // !! ASSIMP_BUILD_NO_TRIANGULATE_PROCESS