void mangle_print(FILE* fptr, struct MangleMask* self, int verbosity)
{
if (!self || verbosity == 0)
return;
size_t npoly;
size_t npix;
npoly = (self->poly_vec != NULL) ? self->poly_vec->size : 0;
npix = (self->pixel_list_vec != NULL) ? self->pixel_list_vec->size : 0;
fprintf(fptr,
"Mangle\n"
"\tfile: %s\n"
"\tarea: %g sqdeg\n"
"\tnpoly: %ld\n"
"\tpixeltype: '%c'\n"
"\tpixelres: %ld\n"
"\tnpix: %ld\n"
"\tsnapped: %d\n"
"\tbalkanized: %d\n"
"\tverbose: %d\n",
self->filename, self->total_area*R2D*R2D,
npoly, self->pixeltype, self->pixelres, npix,
self->snapped, self->balkanized,
self->verbose);
if (verbosity > 1) {
print_polygons(fptr,self->poly_vec);
}
}
int main()
{
// A start-shaped polygon, oriented counter-clockwise as required for outer contours.
Point_2 pts[] = { Point_2(-1,-1)
, Point_2(0,-12)
, Point_2(1,-1)
, Point_2(12,0)
, Point_2(1,1)
, Point_2(0,12)
, Point_2(-1,1)
, Point_2(-12,0)
} ;
std::vector<Point_2> star(pts,pts+8);
// We want an offset contour in the outside.
// Since the package doesn't support that operation directly, we use the following trick:
// (1) Place the polygon as a hole of a big outer frame.
// (2) Construct the skeleton on the interior of that frame (with the polygon as a hole)
// (3) Construc the offset contours
// (4) Identify the offset contour that corresponds to the frame and remove it from the result
double offset = 3 ; // The offset distance
// First we need to determine the proper separation between the polygon and the frame.
// We use this helper function provided in the package.
boost::optional<double> margin = CGAL::compute_outer_frame_margin(star.begin(),star.end(),offset);
// Proceed only if the margin was computed (an extremely sharp corner might cause overflow)
if ( margin )
{
// Get the bbox of the polygon
CGAL::Bbox_2 bbox = CGAL::bbox_2(star.begin(),star.end());
// Compute the boundaries of the frame
double fxmin = bbox.xmin() - *margin ;
double fxmax = bbox.xmax() + *margin ;
double fymin = bbox.ymin() - *margin ;
double fymax = bbox.ymax() + *margin ;
// Create the rectangular frame
Point_2 frame[4]= { Point_2(fxmin,fymin)
, Point_2(fxmax,fymin)
, Point_2(fxmax,fymax)
, Point_2(fxmin,fymax)
} ;
// Instantiate the skeleton builder
SsBuilder ssb ;
// Enter the frame
ssb.enter_contour(frame,frame+4);
// Enter the polygon as a hole of the frame (NOTE: as it is a hole we insert it in the opposite orientation)
ssb.enter_contour(star.rbegin(),star.rend());
// Construct the skeleton
boost::shared_ptr<Ss> ss = ssb.construct_skeleton();
// Proceed only if the skeleton was correctly constructed.
if ( ss )
{
print_straight_skeleton(*ss);
// Instantiate the container of offset contours
ContourSequence offset_contours ;
// Instantiate the offset builder with the skeleton
OffsetBuilder ob(*ss);
// Obtain the offset contours
ob.construct_offset_contours(offset, std::back_inserter(offset_contours));
// Locate the offset contour that corresponds to the frame
// That must be the outmost offset contour, which in turn must be the one
// with the largetst unsigned area.
ContourSequence::iterator f = offset_contours.end();
double lLargestArea = 0.0 ;
for (ContourSequence::iterator i = offset_contours.begin(); i != offset_contours.end(); ++ i )
{
double lArea = CGAL_NTS abs( (*i)->area() ) ; //Take abs() as Polygon_2::area() is signed.
if ( lArea > lLargestArea )
{
f = i ;
lLargestArea = lArea ;
}
}
// Remove the offset contour that corresponds to the frame.
offset_contours.erase(f);
print_polygons(offset_contours);
}
}
return 0;
}
