Segfault when directly calling Polygon.__new__()

[itzpr3d4t0r]

The following program segfaults:

from geometry import Polygon

poly = Polygon.__new__(Polygon)

poly[0] = (1, 2)

This is because the __new__ function in the Polygon class does not allocate the vertices attribute. Instead, it relies on the pgPolygon_FromObject function to handle this. Here is the pg_polygon_new current implementation:

static PyObject *
pg_polygon_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
    pgPolygonObject *self = (pgPolygonObject *)type->tp_alloc(type, 0);

    if (self) {
        self->polygon.vertices = NULL;
        self->polygon.verts_num = 0;
        self->polygon.c_x = 0;
        self->polygon.c_y = 0;
        self->weakreflist = NULL;
    }

    return (PyObject *)self;
}

The issue can be fixed by merging in code change #157 and making the following changes:

• Allocate memory for a double array in the "pg_polygon_new" function, with a minimum size of 6 (since the smallest polygon is a triangle)
• Modify the "polygon init" function in Restructured Polygon internals #157 to resize memory as needed, in case the init function needs to allocate more than 3 vertices.