TODO_static_filters
Special TODO list for the static filters.
-----------------------------------------
It's a lot of work here for a "minor" optimization, so it's "low" priority,
except we could merge stuff with Olivier's Fixed !
- Known problems with the current approach:
- Match operator<(a,b) and co...
- What to do with branches (e.g. collinearC3() and power_test()):
- The epsilon computation type should return ZERO/EQUAL as default.
This way, collinearC3() works.
- The user can provide the epsilon variant inside the source code,
delimited by special symbols /*CGAL_FILTER_BODY ... */. That's the
solution for CGAL.
- Checks that the epsilons have been updated (which will not prove that
it's correct, but is better than nothing).
- Or use G++'s interface as a parser ? See gcc mail archives, 15 august 2000,
"XML output for GCC". An XML description for predicates ?
- /*DEGREE=2*/ attribute to the arguments ?
- # of bounds : one per predicate, or one per argument ? give choice.
- # of epsilons: one per predicate, or one set per sub-predicate ? choice.
- Check that the compiler optimizes the epsilon computation (use
__attribute__((const)) for Static_filter_error operators) ?
- As Fred pointed out: the scheme is not thread safe.
- Remove the assertions in the original code.
- In case there are loops, we must take the max() of the epsilons. This should
not happen often, imho... Wait and see.
- Move static_infos in src/.
- Replace: NEW_bound = max(NEW_bound, fabs(px.to_double())); by: if (NEW_bound
< fabs(px.to_double())) NEW_bound = fabs(px.to_double()); or even, using a
.bound() member function: if (NEW_bound < px.bound()) NEW_bound = px.bound();
Moreover, to_double() is not exact, we should use abs(to_interval(x)).sup() !
- Member function access for generic type should be (?): .dbl_approx()
.bound() (basically a bound on: fabs(.dbl_approx())) .error()
- Add a "number of bits" field in Static_filter_error ? (so that we get the
same thing as Fixed for 24 bits)
- Another approach to consider : Implement predicates taking one or several
epsilons as additional parameters, and have the functionality found in Open
CasCade, using sign(a, epsilon). Then with a special traits or something,
we can define sign(a,epsilon) = sign(a), and get the traditionnal template
predicates from that... So that the epsilons are removed at compile time ?
It would be nice to know exactly the desired functionality for epsilons...
- Where to put the context of the predicates ? different possibilities :
1- static data member of the predicate object (~as it is now)
2- data member of the predicate object
3- static data member of the kernel
4- data member of the kernel
5- global data
Things to take into account :
- I want to be able to initialize the bounds externally.
This can't be done if we choose 2-.
- I want to be able to have different contexts depending where I use the
predicate, this can't be done with 5- nor 3- nor 1-.
- If I add a failure_counter, it should be at the same place as the context,
and I should be able to access it from the outside. If we do that like
triangulation, treating geom_traits as a data member of triangulatino, then
it's ok.
- So it remains 2 possibilities :
a- data member of the predicate object.
b- data member of the kernel.
So 1-, 3-, 5- are out since we can't have different contexts.
2- and 4- are basically equivalent if we can access the context of an object
via the kernel object (_gt in triangulation). So, Orientation_2_object(),
for this particular kernel, would return a const ref to a data member of the
kernel...
So the good choice seems to be to have data stored in each predicate object,
and having the kernel store a predicate object for each predicate.
Then the orientation_2_object() simply returns a reference to it.
Then it means algorithms should use one "global" object per predicate (e.g.
one orientation object for a whole Triangulation). Except for cases where
they actually want different contexts.
// Additional kernel for storage type ?
template <class SK, class EK, class IK = Cartesian<Interval_nt> >
class Filtered_Point_2
{
const CK::Point_2 storage;
// IK cached ? It doesn't make sense to do it lazily because it's going to
// be used. BUT, what is worth is the case when the storage number type is
// like a double : in this case, no approximation needs to be stored.
IK::Point_2 app;
const IK::Point_2 & approx() { return app; }
#if No_cache_EK // via a traits parameter ? Have a generic caching mechanism ?
EK::Point_2 exact() { return EK::Point_2(storage); }
#else
EK::Point_2 ex;
const EK::Point_2 & exact { return ex; }
#endif
};
// For filtered constructions, we should be able to re-use the same predicates,
// but have different constructions and objects Point_2...
template <class EK, class IK = Cartesian<Interval> >
class Filtered_kernel
{
public:
Filtered_kernel()
: ik(), ek(),
orientation_2_obj(ik.orientation_2_object(), ek.orientation_2_object())
// ...
{}
typedef CGAL::Filtered_Point_2<...> Point_2;
// ...
typedef CGAL::Filtered_p_Orientation<IK, EK> Orientation_2;
Orientation_2 orientation_2_obj;
const Orientation_2 & orientation_2_object() const
{ return orientation_2_obj; }
const IK & get_ik() const { return ik; }
const EK & get_ek() const { return ek; }
private:
EK ek;
IK ik;
};
Then you use this thing as a kernel :
Filtered_kernel<Cartesian<leda_real> >
eventually adding profiling template parameters...
Just like we have at the NT level : Lazy_exact_nt<leda_real>.
Maybe have a unique (Cartesian) kernel that includes filtering and caching
capabilities which are toggleable by a simple traits ? The predicate objects
would include the (currently so-called) update_epsilon() member functions...
Or probably better, a filtering wrapper that can be used by homogeneous as
well...