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

From: chun ping wang (cablepuff_at_[hidden])
Date: 2006-08-21 22:36:08

here is the basic header file basicgl.hpp

#include <windows.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>
#include <boost/function.hpp>
#include <boost/static_assert.hpp>
#include <boost/type_traits.hpp>
#include <boost/cast.hpp>

template <class T>
boost::function<void*(const T&, const T&)> getVerxFunc2()
{
   BOOST_STATIC_ASSERT(boost::is_integral<T>::value ||
boost::is_floating_point<T>::value);
   return (boost::is_floating_point<T>::value) ? &glVertex2d : &glVertex2i;
}

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) {
     boost::function<void(const T&, const T&)> myFunc(getVerxFunc2<T>());
     glBegin(GL_POINTS);
        myFunc(x, y);
     glEnd();
     glFlush();
}

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();
}

template <class T>
void drawLine(const T& x1, const T& y1, const T& x2, const T& y2) {
     boost::function<void(const T&, const T&)> myFunc(getVerxFunc2<T>());
     glBegin(GL_LINE);
        myFunc(x1, y1);
        myFunc(x2, y2);
     glEnd();
     glFlush();
}
template <class T>
void drawLine(const T& x1, const T& y1, const T& x2, const T& y2, const T&
z1, const T& z2) {
     boost::function<void(const T&, const T&, const T&)>
myFunc(getVerxFunc3<T>());
     glBegin(GL_LINE);
        myFunc(x1, y1, z1);
        myFunc(x2, y2, z2);
     glEnd();
     glFlush();
}

drawLine(4.1, 5.2, 3.9, 4.2);

When i compile i get the following errors.

16 D:\Data\cs classes\cs450\c++\BasicGL.hpp conditional expression between
distinct pointer types `void (*)(GLdouble, GLdouble)' and `void (*)(GLint,
GLint)' lacks a cast
46 D:\Data\cs classes\cs450\c++\BasicGL.hpp   instantiated from `void
drawLine(const T&, const T&, const T&, const T&) [with T = GLdouble]'
16 D:\Data\cs classes\cs450\c++\BasicGL.hpp invalid conversion from `void
(*)(GLdouble, GLdouble)' to `void*'
16 D:\Data\cs classes\cs450\c++\BasicGL.hpp invalid conversion from `void
(*)(GLint, GLint)' to `void*'
85 D:\Data\Devcpp\include\boost_1_33_1\boost\function\function_template.hpp
ISO C++ forbids casting between pointer-to-function and pointer-to-object

Is there a nice work around this?

Thanks.