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

23 Aug 2006

      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  wrote:
...
On Mon, 21 Aug 2006, chun ping wang wrote:
[...]
...
template <class T>
boost::function 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
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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