Re: [boost] Review manager for Boost QVM?

Subject: Re: [boost] Review manager for Boost QVM?
From: Erik H (ice.rikh_at_[hidden])
Date: 2014-06-06 19:53:45

On Fri, Jun 6, 2014 at 3:00 PM, Emil Dotchevski <emil_at_[hidden]>
wrote:

> On Fri, Jun 6, 2014 at 11:50 AM, Erik H <ice.rikh_at_[hidden]> wrote:
> > Hi Emil,
> >
> > Apologies for being yet another random support requester :)  I use GLM
> > <http://www.g-truc.net/project-0016.html#menu> here and there and boost
> > quite a bit; replacing the GLM dependency with boost::QVM is therefore
> > attractive, assuming it is approved.  As a GLM user, I have a couple
> > questions:
>
> Ha, I didn't mean to imply that I'm annoyed by support questions. :)
>
> > Would I have to use QVM with my own matrix type if I want to feed a QVM
> > matrix to glUniformMatrix4fv without a temp copy?  With GLM, I do this
> > using, for example, glUniformMatrix4fv(fooLoc, 1, GL_FALSE,
> > glm::value_ptr(fooMatrix)).
>
> If a matrix type stores its values as anything but a 1-dimensional
> array in column-major order, you can't (portably) feed it into
> glUniformMatrix4fv without a temporary; at least it'd require a cast,
> which in theory may not work on some platform.
>
> The solution if you use QVM is to define your own matrix type that
> stores the values as an array internally, which would let you pass it
> to OpenGL without a temp:
>
> struct gl_mat4
> {
>   float el[16];
> };
>
> Then you specialize the m_traits type from the QVM library to enable
> the appropriate matrix operations for objects of type gl_mat4:
>
> template <>
> struct m_traits<gl_mat4>
> {
>     static int const rows = 4;
>     static int const cols = 4;
>     typedef float scalar_type;
>
>     template <int R,int C> static scalar_type r( gl_mat4 const & m ) {
> return m.el[C*4+R]; }
>     template <int R,int C> static scalar_type & w( gl_mat4 & m ) {
> return m.el[C*4+R]; }
>
>     static scalar_type ir( int r, int c, gl_mat4 const & m ) { return
> m.el[c*4+r]; }
>     static scalar_type & iw( int r, int c, gl_mat4 & m ) { return
> m.el[c*4+r]; }
> };
>
> Now if you want to pass a gl_mat4 to glUniformMatrix4fv, you just do
> m.el, yet you get all matrix operations automatically working for
> gl_mat4 objects, including if you mix them with other matrix types,
> e.g. the ones that come from the 3D engine you use, or the physics
> simulation library you use, etc.
>
> HTH,
> Emil
>
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Thanks for the comprehensive response!  That's awesome!  It works as you
say with GL, and additionally I had no problem using the same tricks to
make a boost::numpy view of QVM matrix :)  QVM should be a shoo-in, in my
opinion.

-Erik