StlMesher.cpp

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// ==============================================================================================
// Microflow 3D, http://www.microflow.pwr.edu.pl/
// Created by Roman Szafran on 15.03.19.
// Copyright (c) 2019 Wroclaw University of Science and Technology.
// Distributed under the Apache License, Version 2.0. You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0 or see accompanying file license.txt.
// Redistributions of source code must retain the above copyright and license notice.
// ==============================================================================================

#include "StlMesher.h"

        openvdb::FloatGrid::Ptr MF::GB::StlMesher::readSTLGrid(const std::string &fileName, const double voxelSize, const bool verbose) {

            // Read stl grid with tyti stl reader.
            auto STLGrid = std::make_unique<MF::RW::STLReaderTyti>(fileName, verbose);

            // Linear transformation object world-to-grid and grid-to-world coordinates.
            static openvdb::math::Transform::Ptr transformer = {
                    openvdb::math::Transform::createLinearTransform(voxelSize)};

            // Mesh adapter structure required by openvdb meshToVolume.
            struct MeshAdapter {
                const std::vector<tyti::stl::vec3> in_vertices;
                const double in_voxelSize;

                MeshAdapter(tyti::stl::basic_solid<float> &grid, const double voxelSize) : in_vertices(grid.vertices), in_voxelSize(voxelSize) {}
                size_t pointCount() const { return in_vertices.size(); }
                size_t vertexCount(size_t n) const { return 3; }
                size_t vertexCount() const { return 3; }
                size_t polygonCount() const { return pointCount() / vertexCount(); }

                // Return position pos in local grid index space for polygon n and vertex v
                void getIndexSpacePoint(size_t n, size_t v, openvdb::Vec3d &pos) const {
                    const size_t offset = 3 * n + v;
                    const openvdb::Vec3d &vertex = {in_vertices[offset].data[0], in_vertices[offset].data[1],
                                                    in_vertices[offset].data[2]};
                    pos = transformer->worldToIndexCellCentered(vertex).asVec3d();
                    //pos = transformer->worldToIndexNodeCentered(vertex).asVec3d();
                }
            };

            const MeshAdapter mesh_adapter(STLGrid->getSTLGrid_ref().first, voxelSize);
            // Conversion of surface grid to volumetric grid (openvdb level-set grid: inside (-), outside (+)).
            m_VDBGridPtr = openvdb::tools::meshToVolume<openvdb::FloatGrid, MeshAdapter>(mesh_adapter, *transformer, 3.0, 3.0);
            return m_VDBGridPtr;
        }