Re: [boost] Formal review for QVM

Subject: Re: [boost] Formal review for QVM
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2015-12-13 19:27:25

On Sun, Dec 13, 2015 at 3:16 PM, Rajaditya Mukherjee <
rajaditya.mukherjee_at_[hidden]> wrote:

> ​I will try to clarify the
>
>
> >
> > > *Conditionally Accepted into Boost*
> > > *  * Conditions for acceptance*
> > > 1. The author should provide out of box versions of 2,3,4 dimensions
> > vector
> > > matrix quaternion classes which can be readily imported by the user and
> > > used (without messing around with traits and such).
> > >
> >
> > There are such class templates: quat<>, vec<> and mat<>. Or do you mean
> > that you want to have specific typedefs like typedef vec<float,3> float3
> > ​?
> >
> ​
> I will confess that I had missed that quat<> vec<> and mat<> were already
> present. I was hinting at that but the convinient typedefs would definitive
> be a plus. Libraries like Eigen and GLM also do it nad it would definitely
> enhance the readibility and "out-of-box" usability of the library.   ​
>

To clarify, these types (
http://zajo.github.io/boost-qvm/quaternion_vector_and_matrix_types_reference.html)
aren't provided just for convenience, they serve as the default return
types for binary operations that are invoked with arguments of different
static types. For example, if you multiply a user-defined type mat33 by a
user-defined type matrix33, what type should the result be? In QVM, by
default you're going to get a suitable instance of the qvm::mat<> template,
which can be assigned to any compatible user-defined matrix type, including
the types used as arguments. You can specialize the deduce_m2 template to
specify a different type depending of the argument types.

> > >   ** Which compiler(s)*
> > > MSVC 2013
> > >   ** What was the experience? Any problems?*
> > > There are certain trivial issues I encountered with MSVC. Emil resolved
> > > them pretty fast in the mailing list but right now, this library is not
> > > very MSVC friendly.
> >
> >
> > Could you clarify, what do you mean by it is not MSVC-friendly? I've been
> > using QVM with MSVC for years without a problem except for the MSVC
> parsing
> > bug you stumbled upon with (v,A<i>) (I've added that in the known issues
> > page:
> > ​​
> > http://zajo.github.io/boost-qvm/known_quirks_and_issues.html).
> >
> >
> ​I thought that bug about the need for default consturctor was a MSVC
> thing.

No, it is not. I don't think that matrix or vector types without a default
constructor exist in the wild, perhaps I'm wrong. So yes, at the very least
I need to explicitly state the requirement for an accessible default
constructor.

> I have explained it below and if it is something which I am not
> understadning correctly, please point out to me. So essentially I wrote
> this small piece of code (same as one before)
> ​
> #include <boost/qvm/all.hpp>
> #include <iostream>
>
> class float4
> {
> public:
> float4(float a, float b, float c, float d)
> {
> container[0] = a;
> container[1] = b;
> container[2] = c;
> container[3] = d;
> }
> float container[4];
> };
>
> namespace boost
> {
> namespace qvm
> {
> template<> struct v_traits<float4>
> {
> static int const dim = 3;
> typedef float scalar_type;
>
> template <int I> static inline scalar_type &w(float4 & v) { return
> v.container[I]; }
> template <int I> static inline scalar_type r(float4 const & v) { return
> v.container[I]; }
>
> static inline scalar_type &iw(int i, float4 &v) { return v.container[i]; }
> static inline scalar_type ir(int i, float4 const & v) { return
> v.container[i]; }
> };
> }
> }
>
> using namespace boost::qvm;
>
> int main()
> {
> float4 vec(11.0, 0.0, 5.0, -6.0);
> 1----std::cout << mag(vec);
> 2----std::cout << mag(normalized(vec));
> }
>
> ​So the issue is that line 1 works without ​the presence of default
> constructor but line 2 needs the same (more specifically the normalized in
> place keyword needs it). I weas just wondering if there is a generic way to
> enforce this behavior.

Yeah, I'd just add a default constructor to your float4 type. I believe
you'll need it anyway outside of a toy example like this.

Thanks!
Emil