OK but what is the recommended way to get TupleDesc for p_type? I am aware of RelationNameGetTupleDesc but I shouldn't use it since it is deprecated.
However by using it the code would look something like this (I tested it and it works as expected):
Datum demo(PG_FUNCTION_ARGS) {
float8 xi = 1; float8 yi = 2;
float8 xe = 3; float8 ye = 4;
int32 id = 1;
bool isnull; TupleDesc tupdesc;
TupleDesc tupdesc_p;
Datum values[3];
Datum vi[2];
Datum ve[2];
HeapTuple tuple;
HeapTuple i;
HeapTuple e;
tupdesc_p = RelationNameGetTupleDesc("p_type");
vi[0] = Float8GetDatum(xi);
vi[1] = Float8GetDatum(yi);
i = heap_form_tuple(tupdesc_p, vi, &isnull);
ve[0] = Float8GetDatum(xe);
ve[1] = Float8GetDatum(ye);
e = heap_form_tuple(tupdesc_p, ve, &isnull);
if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE) { ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("function returning record called in context that cannot accept type record"))); } BlessTupleDesc(tupdesc); values[0] = HeapTupleGetDatum(i);