int poly_c_center(gpc_vertex_list *vl, double *cx, double *cy){
gpc_vertex *v;
double x=0.0, y=0.0, a;
int i;
for (i=0; i < vl->num_vertices-1; i++) {
v = vl->vertex + i;
a = v->x * (v+1)->y - (v+1)->x * v->y;
x += (v->x + (v+1)->x) * a;
y += (v->y + (v+1)->y) * a;
}
if (! poly_c_is_closed(vl)) {
/* close the loop */
v = vl->vertex + (vl->num_vertices-1);
a = v->x * vl->vertex->y - vl->vertex->x * v->y;
x += (v->x + vl->vertex->x) * a;
y += (v->y + vl->vertex->y) * a;
}
/* this algorithm needs ccw ordered points,
so we have to calculate the order and multiply,
what a waste of cpu power...
If you know a better way, let me know... */
a = 6.0*poly_c_area(vl)*poly_c_orientation(vl);
if (a == 0)
return 1;
*cx = x / a;
*cy = y / a;
return 0;
}
static PyObject *Polygon_orientation(Polygon *self, PyObject *args) {
int i=INDEF;
if (! PyArg_ParseTuple(args, "|i", &i))
return Polygon_Raise(ERR_ARG);
if (i!=INDEF) {
if ((i >= 0) && (i < self->p->num_contours))
return Py_BuildValue("i", poly_c_orientation(self->p->contour+i));
else
return Polygon_Raise(ERR_IND);
} else {
PyObject *OL;
OL = PyTuple_New(self->p->num_contours);
for (i = 0; i < self->p->num_contours; i++)
PyTuple_SetItem(OL, i, PyFloat_FromDouble(poly_c_orientation(self->p->contour+i)));
return Py_BuildValue("O", OL);
}
}