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// -----------------------------------------------------------------------------
//
// Gmsh C tutorial 16
//
// Constructive Solid Geometry, OpenCASCADE geometry kernel
//
// -----------------------------------------------------------------------------
// Instead of constructing a model in a bottom-up fashion with Gmsh's built-in
// geometry kernel, starting with version 3 Gmsh allows you to directly use
// alternative geometry kernels. Here we will use the OpenCASCADE kernel.
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <gmshc.h>
int main(int argc, char **argv)
{
int ierr;
gmshInitialize(argc, argv, 1, 0, &ierr);
gmshModelAdd("t16", &ierr);
// We first create two cubes:
gmshModelOccAddBox(0, 0, 0, 1, 1, 1, 1, &ierr);
if(ierr) {
printf("Could not create OpenCASCADE shapes: bye!");
return 0;
}
gmshModelOccAddBox(0, 0, 0, 0.5, 0.5, 0.5, 2, &ierr);
// We apply a boolean difference to create the "cube minus one eighth" shape:
const int o[] = {3, 1};
const int t[] = {3, 2};
gmshModelOccCut(o, sizeof(o) / sizeof(o[0]), t, sizeof(t) / sizeof(t[0]),
NULL, NULL, NULL, NULL, NULL, 3, 1, 1, &ierr);
// Boolean operations with OpenCASCADE always create new entities. The
// arguments `removeObject' and `removeTool' are set to `1', which will delete
// the original entities.
// We then create the five spheres:
double x = 0, y = 0.75, z = 0, r = 0.09;
int holes[10];
for(int t = 1; t <= 5; t++) {
x += 0.166;
z += 0.166;
gmshModelOccAddSphere(x, y, z, r, 3 + t, -M_PI / 2, M_PI / 2, 2 * M_PI, &ierr);
holes[2 * (t - 1)] = 3;
holes[2 * (t - 1) + 1] = 3 + t;
}
// If we had wanted five empty holes we would have used `gmshModelOccCut()'
// again. Here we want five spherical inclusions, whose mesh should be
// conformal with the mesh of the cube: we thus use `gmshModelOccFragment()',
// which intersects all volumes in a conformal manner (without creating
// duplicate interfaces):
const int o2[] = {3, 3};
int *ov, **ovv;
size_t ov_n, *ovv_n, ovv_nn;
gmshModelOccFragment(o2, sizeof(o) / sizeof(o[0]),
holes, sizeof(holes) / sizeof(holes[0]),
&ov, &ov_n, &ovv, &ovv_n, &ovv_nn, -1, 1, 1, &ierr);
// ov contains all the generated entities of the same dimension as the input
// entities:
printf("fragment produced volumes: ");
for(int i = 0; i < ov_n; i += 2)
printf("(%d, %d) ", ov[i], ov[i + 1]);
printf("\n");
// ovv contains the parent-child relationships for all the input entities:
for(size_t i = 0; i < ovv_nn; i++) {
printf("parent (3, %d) -> child", !i ? o2[1] : holes[(i - 1) * 2 + 1]);
for(size_t j = 0; j < ovv_n[i]; j += 2) {
printf(" (%d, %d)", ovv[i][j], ovv[i][j + 1]);
}
printf("\n");
}
gmshModelOccSynchronize(&ierr);
// When the boolean operation leads to simple modifications of entities, and
// if one deletes the original entities, Gmsh tries to assign the same tag to
// the new entities. (This behavior is governed by the
// `Geometry.OCCBooleanPreserveNumbering' option.)
// Here the `Physical Volume' definitions can thus be made for the 5 spheres
// directly, as the five spheres (volumes 4, 5, 6, 7 and 8), which will be
// deleted by the fragment operations, will be recreated identically (albeit
// with new surfaces) with the same tags:
for(int i = 1; i <= 5; i++) {
const int gi[] = {3 + i};
gmshModelAddPhysicalGroup(3, gi, sizeof(gi) / sizeof(gi[0]), i, "", &ierr);
}
// The tag of the cube will change though, so we need to access it
// programmatically:
const int g[] = {ov[0]};
gmshModelAddPhysicalGroup(3, g, sizeof(g) / sizeof(g[0]), 10, "", &ierr);
gmshFree(ov);
for(int i = 0; i < ovv_nn; i++)
gmshFree(ovv[i]);
gmshFree(ovv_n);
// Creating entities using constructive solid geometry is very powerful, but
// can lead to practical issues for e.g. setting mesh sizes at points, or
// identifying boundaries.
// To identify points or other bounding entities you can take advantage of the
// `gmshModelGetEntities()', `gmshModelGetBoundary()' and
// `gmshModelGetEntitiesInBoundingBox()' functions:
double lcar1 = .1;
double lcar2 = .0005;
double lcar3 = .055;
// Assign a mesh size to all the points:
gmshModelGetEntities(&ov, &ov_n, 0, &ierr);
gmshModelMeshSetSize(ov, ov_n, lcar1, &ierr);
gmshFree(ov);
// Override this constraint on the points of the five spheres:
gmshModelGetBoundary(holes, sizeof(holes) / sizeof(holes[0]),
&ov, &ov_n, 0, 0, 1, &ierr);
gmshModelMeshSetSize(ov, ov_n, lcar3, &ierr);
gmshFree(ov);
// Select the corner point by searching for it geometrically:
double eps = 1e-3;
gmshModelGetEntitiesInBoundingBox(0.5 - eps, 0.5 - eps, 0.5 - eps,
0.5 + eps, 0.5 + eps, 0.5 + eps,
&ov, &ov_n, 0, &ierr);
gmshModelMeshSetSize(ov, ov_n, lcar2, &ierr);
gmshFree(ov);
gmshModelMeshGenerate(3, &ierr);
gmshWrite("t16.msh", &ierr);
// Launch the GUI to see the results:
int gui = 1;
for(int i = 0; i < argc; i++) {
if(!strcmp(argv[i], "-nopopup")) {
gui = 0;
break;
}
}
if(gui) gmshFltkRun(&ierr);
gmshFinalize(&ierr);
return 0;
}
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