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t1.cpp

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    t1.cpp 3.33 KiB
    // This file reimplements gmsh/tutorial/t1.geo in C++.
    
    // For all the elementary explanations about the general philosphy of entities
    // in Gmsh, see the comments in the .geo file. Comments here focus on the
    // specifics of the C++ API.
    
    // The Gmsh API is entirely defined in the <gmsh.h> header:
    #include <gmsh.h>
    
    int main(int argc, char **argv)
    {
      // Before using any functions in the C++ API, Gmsh must be initialized.
      gmshInitialize();
    
      // By default Gmsh will not print out any messages: in order to output
      // messages on the terminal, just set the standard Gmsh option
      // "General.Terminal" (same format and meaning as in .geo files) using
      // gmshOptionSetNumber():
      gmshOptionSetNumber("General.Terminal", 1);
    
      // This creates a new model, named "t1". If gmshModelCreate() is not called, a
      // new default (unnamed) model will be created on the fly, if necessary.
      gmshModelCreate("t1");
    
      // The C++ API provides direct access to the internal CAD kernels. The
      // built-in CAD kernel was used in t1.geo: the corresponding API functions
      // have the "gmshModeGeo" prefix. To create geometrical points with the
      // built-in CAD kernel, one thus uses gmshModelGeoAddPoint():
      //
      // - the first 3 arguments are the point coordinates (x, y, z)
      //
      // - the next (optional) argument is the target mesh size close to the point
      //
      // - the last (optional) argument is the point tag
      double lc = 1e-2;
      gmshModelGeoAddPoint(0, 0, 0, lc, 1);
      gmshModelGeoAddPoint(.1, 0,  0, lc, 2);
      gmshModelGeoAddPoint(.1, .3, 0, lc, 3);
      gmshModelGeoAddPoint(0,  .3, 0, lc, 4);
    
      // The API to create lines with the built-in kernel follows the same
      // conventions: the first 2 arguments are point tags, the last (optional one)
      // is the line tag.
      gmshModelGeoAddLine(1, 2, 1);
      gmshModelGeoAddLine(3, 2, 2);
      gmshModelGeoAddLine(3, 4, 3);
      gmshModelGeoAddLine(4, 1, 4);
    
      // The philosophy to construct line loops and surfaces is similar: the first
      // argument is now a vector of integers.
      gmshModelGeoAddLineLoop({4, 1, -2, 3}, 1);
      gmshModelGeoAddPlaneSurface({1}, 1);
    
      // Physical groups are defined by providing the dimension of the group (0 for
      // physical points, 1 for physical lines, 2 for physical surfaces and 3 for
      // phsyical volumes) followed by a vector of entity tags. The last (optional)
      // argument is the tag of the new group to create.
      gmshModelAddPhysicalGroup(0, {1, 2}, 1);
      gmshModelAddPhysicalGroup(1, {1, 2}, 2);
      gmshModelAddPhysicalGroup(2, {1}, 6);
    
      // Physical names are also defined by providing the dimension and tag of the
      // entity.
      gmshModelSetPhysicalName(2, 6, "My surface");
    
      // Before it can be meshed, the internal CAD representation must be
      // synchronized with the Gmsh model, which will create the relevant Gmsh data
      // structures. This is achieved by the gmshModelGeoSynchronize() API call for
      // the built-in CAD kernel. Synchronizations can be called at any time, but
      // they involve a non trivial amount of processing; so while you could
      // synchronize the internal CAD data after every CAD command, it is usually
      // better to minimize the number of synchronization points.
      gmshModelGeoSynchronize();
    
      // We can then generate a 2D mesh...
      gmshModelMesh(2);
    
      // ... and save it to disk
      gmshExport("t1.msh");
    
      // This should be called at the end:
      gmshFinalize();
      return 0;
    }