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// -----------------------------------------------------------------------------
//
// Gmsh C++ tutorial 7
//
// Background meshes
//
// -----------------------------------------------------------------------------
#include <set>
#include <gmsh.h>
// Mesh sizes can be specified very accurately by providing a background mesh,
// i.e., a post-processing view that contains the target mesh sizes.
int main(int argc, char **argv)
{
gmsh::initialize();
// Merge a list-based post-processing view containing the target mesh sizes:
try {
gmsh::merge("../t7_bgmesh.pos");
} catch(...) {
gmsh::logger::write("Could not load background mesh: bye!");
gmsh::finalize();
return 0;
}
// If the post-processing view was model-based instead of list-based (i.e. if
// it was based on an actual mesh), we would need to create a new model to
// contain the geometry so that meshing it does not destroy the background
// mesh. It's not necessary here since the view is list-based, but it does no
// harm:
gmsh::model::add("t7");
// Create a simple rectangular geometry:
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();
// Add the post-processing view as a new size field:
int bg_field = gmsh::model::mesh::field::add("PostView");
gmsh::model::mesh::field::setNumber(bg_field, "ViewIndex", 0);
// Apply the view as the current background mesh size field:
gmsh::model::mesh::field::setAsBackgroundMesh(bg_field);
// In order to compute the mesh sizes from the background mesh only, and
// disregard any other size constraints, one can set:
gmsh::option::setNumber("Mesh.MeshSizeExtendFromBoundary", 0);
gmsh::option::setNumber("Mesh.MeshSizeFromPoints", 0);
gmsh::option::setNumber("Mesh.MeshSizeFromCurvature", 0);
// See `t10.cpp' for additional information: background meshes are actually a
// particular case of general "mesh size fields".
gmsh::model::mesh::generate(2);
gmsh::write("t7.msh");
// Launch the GUI to see the results:
std::set<std::string> args(argv, argv + argc);
if(!args.count("-nopopup")) gmsh::fltk::run();
gmsh::finalize();
return 0;
}
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