t3.cpp

// -----------------------------------------------------------------------------
//
//  Gmsh C++ tutorial 3
//
//  Extruded meshes, ONELAB parameters, options
//
// -----------------------------------------------------------------------------

#include <set>
#include <cmath>
#include <gmsh.h>

int main(int argc, char **argv)
{
  gmsh::initialize(argc, argv);

  auto createGeometryAndMesh = []()
  {
    // Clear all models and create a new one
    gmsh::clear();
    gmsh::model::add("t3");

    // Copied from `t1.cpp'...
    double lc = 1e-2;
    gmsh::model::geo::addPoint(0, 0, 0, lc, 1);
    gmsh::model::geo::addPoint(.1, 0, 0, lc, 2);
    gmsh::model::geo::addPoint(.1, .3, 0, lc, 3);
    gmsh::model::geo::addPoint(0, .3, 0, lc, 4);
    gmsh::model::geo::addLine(1, 2, 1);
    gmsh::model::geo::addLine(3, 2, 2);
    gmsh::model::geo::addLine(3, 4, 3);
    gmsh::model::geo::addLine(4, 1, 4);
    gmsh::model::geo::addCurveLoop({4, 1, -2, 3}, 1);
    gmsh::model::geo::addPlaneSurface({1}, 1);
    gmsh::model::geo::synchronize();
    gmsh::model::addPhysicalGroup(1, {1, 2, 4}, 5);
    gmsh::model::addPhysicalGroup(2, {1}, -1, "My surface");

    // As in `t2.cpp', we plan to perform an extrusion along the z axis.  But
    // here, instead of only extruding the geometry, we also want to extrude the
    // 2D mesh. This is done with the same `extrude()' function, but by
    // specifying element 'Layers' (2 layers in this case, the first one with 8
    // subdivisions and the second one with 2 subdivisions, both with a height
    // of h/2). The number of elements for each layer and the (end) height of
    // each layer are specified in two vectors:
    double h = 0.1;
    std::vector<std::pair<int, int> > ov;
    gmsh::model::geo::extrude({{2, 1}}, 0, 0, h, ov, {8, 2}, {0.5, 1});

    // The extrusion can also be performed with a rotation instead of a
    // translation, and the resulting mesh can be recombined into prisms (we use
    // only one layer here, with 7 subdivisions). All rotations are specified by
    // an an axis point (-0.1, 0, 0.1), an axis direction (0, 1, 0), and a
    // rotation angle (-Pi/2):
    gmsh::model::geo::revolve({{2, 28}}, -0.1, 0, 0.1, 0, 1, 0, -M_PI / 2, ov,
                              {7});

    // Using the built-in geometry kernel, only rotations with angles < Pi are
    // supported. To do a full turn, you will thus need to apply at least 3
    // rotations. The OpenCASCADE geometry kernel does not have this limitation.

    // A translation (-2 * h, 0, 0) and a rotation ((0, 0.15, 0.25), (1, 0, 0),
    // angle * Pi / 180) can also be combined to form a "twist". The last
    // (optional) argument for the extrude() and twist() functions specifies
    // whether the extruded mesh should be recombined or not. The `angle'
    // parameter is retrieved from the ONELAB database (it can be set
    // interactively in the GUI -- see below):
    std::vector<double> angle;
    gmsh::onelab::getNumber("Parameters/Twisting angle", angle);
    gmsh::model::geo::twist({{2, 50}}, 0, 0.15, 0.25, -2 * h, 0, 0, 1, 0, 0,
                            angle[0] * M_PI / 180., ov, {10}, {}, true);

    gmsh::model::geo::synchronize();

    // All the extrusion functions return a vector of extruded entities: the
    // "top" of the extruded surface (in `ov[0]'), the newly created volume (in
    // `ov[1]') and the tags of the lateral surfaces (in `ov[2]', `ov[3]', ...).

    // We can then define a new physical volume (with tag 101) to group all the
    // elementary volumes:
    gmsh::model::addPhysicalGroup(3, {1, 2, ov[1].second}, 101);

    gmsh::model::mesh::generate(3);
    gmsh::write("t3.msh");
  };

  // Let us now change some options... Since all interactive options are
  // accessible through the API, we can for example make point tags visible or
  // redefine some colors:
  gmsh::option::setNumber("Geometry.PointNumbers", 1);
  gmsh::option::setColor("Geometry.Color.Points", 255, 165, 0);
  gmsh::option::setColor("General.Color.Text", 255, 255, 255);
  gmsh::option::setColor("Mesh.Color.Points", 255, 0, 0);

  // Note that for conciseness "Color." can be ommitted in color options:
  int r, g, b, a;
  gmsh::option::getColor("Geometry.Points", r, g, b, a);
  gmsh::option::setColor("Geometry.Surfaces", r, g, b, a);

  // We create a ONELAB parameter to define the angle of the twist. ONELAB
  // parameters can be modified interactively in the GUI, and can be exchanged
  // with other codes connected to the same ONELAB database. The database can be
  // accessed through the Gmsh C++ API using JSON-formatted strings (see
  // https://gitlab.onelab.info/doc/tutorials/-/wikis/ONELAB-JSON-interface for
  // more information):
  gmsh::onelab::set(R"( [
  {
    "type":"number",
    "name":"Parameters/Twisting angle",
    "values":[90],
    "min":0,
    "max":120,
    "step":1
  }
  ] )");

  // Create the geometry and mesh it:
  createGeometryAndMesh();

  // Launch the GUI and handle the "check" event (recorded in the
  // "ONELAB/Action" parameter) to recreate the geometry with a new twisting
  // angle if necessary:
  auto checkForEvent = [=]() -> bool {
    std::vector<std::string> action;
    gmsh::onelab::getString("ONELAB/Action", action);
    if(action.size() && action[0] == "check") {
      gmsh::onelab::setString("ONELAB/Action", {""});
      createGeometryAndMesh();
      gmsh::graphics::draw();
    }
    return true;
  };

  std::set<std::string> args(argv, argv + argc);
  if(!args.count("-nopopup")) {
    gmsh::fltk::initialize();
    while(gmsh::fltk::isAvailable() && checkForEvent())
      gmsh::fltk::wait();
  }

  // When the GUI is launched, you can use the `Help->Current Options and
  // Workspace' menu to see the current values of all options. To save the
  // options in a file, use `File->Export->Gmsh Options', or through the api:

  // gmsh::write("t3.opt");

  gmsh::finalize();

  return 0;
}