Re: [Boost-users] opengl and boost::function casting problems. .

From: chun ping wang (cablepuff_at_[hidden])
Date: 2006-08-22 22:36:13

Hi, sorry for another problem... i have a simple question to ask...

lets say say i have base class

struct GeomObject
{
  // draws an wire shape
   virtual void drawAbstract(const GLfloat& x, const GLfloat& y, const
GLfloat& z) = 0;
   // draws a solid shape.
   virtual void drawSolid(const GLfloat& x, const GLfloat& y, const GLfloat&
z) = 0;
}

Now i have bunch of stuff that inherits it..

Like class Circle, class Sphere, class Cylinder, class Cone and all of them
implement drawSolid and drawAbstract (radius base assumed).

I have a function call drawCircle(const std::string& r,
(someBoostFunctionParam))
{
    Circle cir(4.0, r); // construct a circle with radius 4.0 and name r
    cir.someBoostFunctionParam(x, y, z);
}

thus if i say drawCircle("solid", &Circle::drawSolid);
drawCircle("abstract", &Circle::drawAbstract);

How do you do that? Or whats the best way to do it.

On 8/22/06, François Duranleau <duranlef_at_[hidden]> wrote:
>
> On Mon, 21 Aug 2006, chun ping wang wrote:
>
> [...]
> > template <class T>
> > boost::function<void*(const T&, const T&, const T&)> getVerxFunc3()
> > {
> >  BOOST_STATIC_ASSERT(boost::is_integral<T>::value ||
> > boost::is_floating_point<T>::value);
> >  return (boost::is_integral<T>::value) ? &glVertex3i : &glVertex3d;
> > }
> >
> [...]
> >
> > template <class T>
> > void drawDot(const T& x, const T& y, const T& z) {
> >    boost::function<void(const T&, const T&, const T&)>
> > myFunc(getVerxFunc3<T>());
> >    glBegin(GL_POINTS);
> >       myFunc(x, y, z);
> >    glEnd();
> >    glFlush();
> > }
> >
> [just kept one example from the above]
>
> Isn't using boost::function overkill here? I would rather do this:
>
> template < typename T >
> void gl_vertex( const T& x , const T& y , const T& z )
> {
>     // you can use the BOOST_STATIC_ASSERT as above here, or use
>     // boost::enable_if with the same condition around the void return
>
>     if ( boost::is_floating_point< T >::value )
>     {
>         glVertex3d( x , y , z ) ;
>     }
>     else
>     {
>         glVertex3i( x , y , z ) ;
>     }
> }
>
> or even simply this:
>
> void gl_vertex( GLdouble x , GLdouble y , GLdouble z )
> {
>     glVertex3d( x , y , z ) ;
> }
>
> void gl_vertex( GLint x , GLint y , GLint z )
> {
>     glVertex3i( x , y , z ) ;
> }
>
> and then:
>
> template < typename T >
> void drawDot( const T& x , const T& y , const T& z )
> {
>     glBegin( GL_POINTS ) ;
>     gl_vertex( x , y , z ) ;
>     glEnd() ;
> }
>
> That should be more efficient and, especially for the second case, is a
> simpler to read overall.
>
> Anyway, just my two cents.
>
> --
> François Duranleau
> LIGUM, Université de Montréal
>
> "Sacrifices are a necessary factor in creating a new destiny. A small
> misfortune becomes the cornerstone of a greater happiness."
>                          - Emperor Dornkirk, in _The Vision of Escaflowne_
>
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