Segfault and unwanted behaviour in Line conversion

[itzpr3d4t0r]

While working on #194 i discovered two major issues.

The first one is that you can create a Line object from a Rect

r = Rect(0, 0, 100, 100)
l = Line(r) # returns a Line(0, 0, 100, 100)

This is not fine as any function that takes in a Line or Line-like object also accepts a Rect. I don't think we should support this behaviour.

The second thing is that doing the same with a Polygon with 4 vertices results in a segfault:

p = Polygon((0, 0), (100, 0), (100, 100), (0, 100))
l = Line(p)

I've investigated a bit and founf that it's caused by the pgLine_FromObject function, responsible for extracting a Line struct from a single object. Issue is that both rect and Polygon count as Sequences, that are then treated in that function with this piece of code:

if (PySequence_Check(obj)) {
        length = PySequence_Length(obj);
        if (length == 4) {
            PyObject *tmp;
            tmp = PySequence_GetItem(obj, 0);
            if (!pg_DoubleFromObj(tmp, &(out->x1))) {
                Py_DECREF(tmp);
                return 0;
            }
            Py_DECREF(tmp);
            tmp = PySequence_GetItem(obj, 1);
            if (!pg_DoubleFromObj(tmp, &(out->y1))) {
                Py_DECREF(tmp);
                return 0;
            }
            Py_DECREF(tmp);
            tmp = PySequence_GetItem(obj, 2);
            if (!pg_DoubleFromObj(tmp, &(out->x2))) {
                Py_DECREF(tmp);
                return 0;
            }
            Py_DECREF(tmp);
            tmp = PySequence_GetItem(obj, 3);
            if (!pg_DoubleFromObj(tmp, &(out->y2))) {
                Py_DECREF(tmp);
                return 0;
            }
            Py_DECREF(tmp);
            return IS_LINE_VALID(out);
        }
        ...

So when the sequence has length 4 (that are exactly the rect and Polygon with 4 vertices cases) issues arise

[itzpr3d4t0r]

Btw i partially fixed this (only for polygons) in #194 and yeah UPDATE: this is true for Circle as well: #189.

[Emc2356]

i dont not consider this an issue, this functions are designed to take a sequence and Polygon/Rect/Line are considered sequences